2021
Zhuang, Yizhou; Fu, Rong; Santer, Benjamin D.; Dickinson, Robert E.; Hall, Alex
Quantifying contributions of natural variability and anthropogenic forcings on increased fire weather risk over the western United States Journal Article
In: Proceedings of the National Academy of Sciences, vol. 118, no. 45, pp. e2111875118, 2021.
@article{2310,
title = {Quantifying contributions of natural variability and anthropogenic forcings on increased fire weather risk over the western United States},
author = {Yizhou Zhuang and Rong Fu and Benjamin D. Santer and Robert E. Dickinson and Alex Hall},
url = {https://www.pnas.org/content/118/45/e2111875118},
year = {2021},
date = {2021-01-01},
journal = {Proceedings of the National Academy of Sciences},
volume = {118},
number = {45},
pages = {e2111875118},
abstract = {Previous studies have identified a recent increase in wildfire activity in the western United States (WUS). However, the extent to which this trend is due to weather pattern changes dominated by natural variability versus anthropogenic warming has been unclear. Using an ensemble constructed flow analogue approach, we have employed observations to estimate vapor pressure deficit (VPD), the leading meteorological variable that controls wildfires, associated with different atmospheric circulation patterns. Our results show that for the period 1979 to 2020, variation in the atmospheric circulation explains, on average, only 32% of the observed VPD trend of 0.48 ± 0.25 hPa/decade (95% CI) over the WUS during the warm season (May to September). The remaining 68% of the upward VPD trend is likely due to anthropogenic warming. The ensemble simulations of climate models participating in the sixth phase of the Coupled Model Intercomparison Project suggest that anthropogenic forcing explains an even larger fraction of the observed VPD trend (88%) for the same period and region. These models and observational estimates likely provide a lower and an upper bound on the true impact of anthropogenic warming on the VPD trend over the WUS. During August 2020, when the August Complex “Gigafire” occurred in the WUS, anthropogenic warming likely explains 50% of the unprecedented high VPD anomalies.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Previous studies have identified a recent increase in wildfire activity in the western United States (WUS). However, the extent to which this trend is due to weather pattern changes dominated by natural variability versus anthropogenic warming has been unclear. Using an ensemble constructed flow analogue approach, we have employed observations to estimate vapor pressure deficit (VPD), the leading meteorological variable that controls wildfires, associated with different atmospheric circulation patterns. Our results show that for the period 1979 to 2020, variation in the atmospheric circulation explains, on average, only 32% of the observed VPD trend of 0.48 ± 0.25 hPa/decade (95% CI) over the WUS during the warm season (May to September). The remaining 68% of the upward VPD trend is likely due to anthropogenic warming. The ensemble simulations of climate models participating in the sixth phase of the Coupled Model Intercomparison Project suggest that anthropogenic forcing explains an even larger fraction of the observed VPD trend (88%) for the same period and region. These models and observational estimates likely provide a lower and an upper bound on the true impact of anthropogenic warming on the VPD trend over the WUS. During August 2020, when the August Complex “Gigafire” occurred in the WUS, anthropogenic warming likely explains 50% of the unprecedented high VPD anomalies.
Marengo, J.; Espinoza, C.; Fu, R.; Munoz, J. C. J.; Alves, L. M.; Rocha, H. R.; Schongart, J.
In: 2021.
@inbook{2308,
title = {Long-term variability, extremes and changes in temperature and hydro meteorology, Ch. 22, Working Group 8: Climate Change in the Amazon: Tendences, Impacts and Ecological Consequences, Science Panel for the Amazon (SPA) 2021 Report},
author = {J. Marengo and C. Espinoza and R. Fu and J. C. J. Munoz and L. M. Alves and H. R. Rocha and J. Schongart},
url = {https://www.theamazonwewant.org/wp-content/uploads/2021/07/SPA-Chapter-22-PC-climate-change-in-the-amazon-tendencies-impacts-and-ecological-consequences.pdf},
year = {2021},
date = {2021-01-01},
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Zhou, W.; Guan, K.; Peng, B.; Wang, Z.; Fu, R.; Li, B.; Ainsworth, E. A.; DeLucia, E.; Zhao, L.; Chen, Z.
A generic risk assessment framework to evaluate historical and future climate-induced risk for rainfed corn and soybean yield in the US Midwest Journal Article
In: Weather and Climate Extremes, vol. 33, 2021.
@article{2307,
title = {A generic risk assessment framework to evaluate historical and future climate-induced risk for rainfed corn and soybean yield in the US Midwest},
author = {W. Zhou and K. Guan and B. Peng and Z. Wang and R. Fu and B. Li and E. A. Ainsworth and E. DeLucia and L. Zhao and Z. Chen},
year = {2021},
date = {2021-01-01},
journal = {Weather and Climate Extremes},
volume = {33},
keywords = {},
pubstate = {published},
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Worden, John; Saatchi, Sassan; Keller, Michael; Bloom, A. Anthony; Liu, Junjie; Parazoo, Nicholas; Fisher, Joshua B.; Bowman, Kevin; Reager, John T.; Fahy, Kristen; Schimel, David; Fu, Rong; Worden, Sarah; Yin, Yi; Gentine, Peirre; Konings, Alexandra G.; Quetin, Gregory R.; Williams, Mathew; Worden, Helen; Shi, Mingjie; Barkhordarian, Armineh
Satellite Observations of the Tropical Terrestrial Carbon Balance and Interactions With the Water Cycle During the 21st Century Journal Article
In: Review of Geophysics, vol. 59, no. 1, 2021.
@article{2302,
title = {Satellite Observations of the Tropical Terrestrial Carbon Balance and Interactions With the Water Cycle During the 21st Century},
author = {John Worden and Sassan Saatchi and Michael Keller and A. Anthony Bloom and Junjie Liu and Nicholas Parazoo and Joshua B. Fisher and Kevin Bowman and John T. Reager and Kristen Fahy and David Schimel and Rong Fu and Sarah Worden and Yi Yin and Peirre Gentine and Alexandra G. Konings and Gregory R. Quetin and Mathew Williams and Helen Worden and Mingjie Shi and Armineh Barkhordarian},
url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020RG000711},
year = {2021},
date = {2021-01-01},
journal = {Review of Geophysics},
volume = {59},
number = {1},
abstract = {A constellation of satellites is now in orbit providing information about terrestrial carbon and water storage and fluxes. These combined observations show that the tropical biosphere has changed significantly in the last 2 decades from the combined effects of climate variability and land use. Large areas of forest have been cleared in both wet and dry forests, increasing the source of carbon to the atmosphere. Concomitantly, tropical fire emissions have declined, at least until 2016, from changes in land-use practices and rainfall, increasing the net carbon sink. Measurements of carbon stocks and fluxes from disturbance and recovery and of vegetation photosynthesis show significant regional variability of net biosphere exchange and gross primary productivity across the tropics and are tied to seasonal and interannual changes in water fluxes and storage. Comparison of satellite based estimates of evapotranspiration, photosynthesis, and the deuterium content of water vapor with patterns of total water storage and rainfall demonstrate the presence of vegetation-atmosphere interactions and feedback mechanisms across tropical forests. However, these observations of stocks, fluxes and inferred interactions between them do not point unambiguously to either positive or negative feedbacks in carbon and water exchanges. These ambiguities highlight the need for assimilation of these new measurements with Earth System models for a consistent assessment of process interactions, along with focused field campaigns that integrate ground, aircraft and satellite measurements, to quantify the controlling carbon and water processes and their feedback mechanisms.},
keywords = {},
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A constellation of satellites is now in orbit providing information about terrestrial carbon and water storage and fluxes. These combined observations show that the tropical biosphere has changed significantly in the last 2 decades from the combined effects of climate variability and land use. Large areas of forest have been cleared in both wet and dry forests, increasing the source of carbon to the atmosphere. Concomitantly, tropical fire emissions have declined, at least until 2016, from changes in land-use practices and rainfall, increasing the net carbon sink. Measurements of carbon stocks and fluxes from disturbance and recovery and of vegetation photosynthesis show significant regional variability of net biosphere exchange and gross primary productivity across the tropics and are tied to seasonal and interannual changes in water fluxes and storage. Comparison of satellite based estimates of evapotranspiration, photosynthesis, and the deuterium content of water vapor with patterns of total water storage and rainfall demonstrate the presence of vegetation-atmosphere interactions and feedback mechanisms across tropical forests. However, these observations of stocks, fluxes and inferred interactions between them do not point unambiguously to either positive or negative feedbacks in carbon and water exchanges. These ambiguities highlight the need for assimilation of these new measurements with Earth System models for a consistent assessment of process interactions, along with focused field campaigns that integrate ground, aircraft and satellite measurements, to quantify the controlling carbon and water processes and their feedback mechanisms.
Ma, Hsi-Yen; Zhang, Kai; Tang, Shuaiqi; Xie, Shaocheng; Fu, Rong
Evaluation of the Causes of Wet-Season Dry Biases Over Amazonia in CAM5 Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 126, no. 11, 2021.
@article{2301,
title = {Evaluation of the Causes of Wet-Season Dry Biases Over Amazonia in CAM5},
author = {Hsi-Yen Ma and Kai Zhang and Shuaiqi Tang and Shaocheng Xie and Rong Fu},
url = {https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2020JD033859},
year = {2021},
date = {2021-01-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {126},
number = {11},
abstract = {This study investigates the causes of pronounced low precipitation bias over Amazonia in the Community Atmosphere Model version 5 (CAM5), a common feature in many global climate models. Our analysis is based on a suite of 3-day long hindcasts starting every day at 00Z from 1997 to 2012 and an AMIP simulation for the same period. The Amazonia dry bias appears by the second day in the hindcasts and is very robust for all the seasons with the largest bias magnitude during the wet season (December–February). The bias pattern and magnitude do not change much during different dynamical wind regimes on sub-seasonal time scales. We further classify the diurnal cycle of precipitation near the LBA sites from observations and hindcasts into three convective regimes: no precipitation, late afternoon deep convection, and nighttime deep convection. CAM5 can only simulate the late afternoon convective regime and completely fails to simulate the nighttime convection, which is mostly from propagating convective systems originating from remote locations. CAM5 mainly underestimates precipitation in the late afternoon and nighttime convective regimes, which occur during ~67% of wet season days and account for ~75% of accumulated precipitation amount in observations. The persistent warm temperature bias and slightly higher moisture below 850 mb likely trigger deep convection too frequently, resulting in an earlier but weaker rainfall peak in the diurnal cycle. Furthermore, shallow convection may not effectively transport moisture from boundary layer to the free atmosphere, which also leads to weaker deep convection events.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study investigates the causes of pronounced low precipitation bias over Amazonia in the Community Atmosphere Model version 5 (CAM5), a common feature in many global climate models. Our analysis is based on a suite of 3-day long hindcasts starting every day at 00Z from 1997 to 2012 and an AMIP simulation for the same period. The Amazonia dry bias appears by the second day in the hindcasts and is very robust for all the seasons with the largest bias magnitude during the wet season (December–February). The bias pattern and magnitude do not change much during different dynamical wind regimes on sub-seasonal time scales. We further classify the diurnal cycle of precipitation near the LBA sites from observations and hindcasts into three convective regimes: no precipitation, late afternoon deep convection, and nighttime deep convection. CAM5 can only simulate the late afternoon convective regime and completely fails to simulate the nighttime convection, which is mostly from propagating convective systems originating from remote locations. CAM5 mainly underestimates precipitation in the late afternoon and nighttime convective regimes, which occur during ~67% of wet season days and account for ~75% of accumulated precipitation amount in observations. The persistent warm temperature bias and slightly higher moisture below 850 mb likely trigger deep convection too frequently, resulting in an earlier but weaker rainfall peak in the diurnal cycle. Furthermore, shallow convection may not effectively transport moisture from boundary layer to the free atmosphere, which also leads to weaker deep convection events.
Fu, Rong; Simpson, Isla; Mankin, Justin; Hoell, Andrew; Barrie, Daniel
Fueled by climate change, costly Southwest drought isn’t going away newspaperarticle
2021.
@newspaperarticle{2299,
title = {Fueled by climate change, costly Southwest drought isn’t going away},
author = {Rong Fu and Isla Simpson and Justin Mankin and Andrew Hoell and Daniel Barrie},
url = {https://www.washingtonpost.com/weather/2021/09/21/southwest-drought-extreme-climate-noaa/},
year = {2021},
date = {2021-01-01},
journal = {The Washington Post},
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pubstate = {published},
tppubtype = {newspaperarticle}
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Mankin, J. S.; Simpson, I.; Hoell, A.; Fu, R.; Lisonbee, J.; Sheffield, A.; Barrie, D.
NOAA Drought Task Force Report on the 2020–2021 Southwestern U.S. Drought report
2021.
@report{2298,
title = {NOAA Drought Task Force Report on the 2020-2021 Southwestern U.S. Drought},
author = {J. S. Mankin and I. Simpson and A. Hoell and R. Fu and J. Lisonbee and A. Sheffield and D. Barrie},
url = {https://cpo.noaa.gov/MAPP/DTF4SWReport},
year = {2021},
date = {2021-01-01},
institution = {NOAA Drought Task Force Report on the 2020–2021 Southwestern U.S. Drought},
keywords = {},
pubstate = {published},
tppubtype = {report}
}
Jiang, Yelin; Wang, Guiling; Liu, Weiguang; Erfanian, Amir; Peng, Qing; Fu, Rong
Modeled Response of South American Climate to Three Decades of Deforestation Journal Article
In: Journal of Climate, vol. 34, no. 6, pp. 2189-2203, 2021.
@article{2293,
title = {Modeled Response of South American Climate to Three Decades of Deforestation},
author = {Yelin Jiang and Guiling Wang and Weiguang Liu and Amir Erfanian and Qing Peng and Rong Fu},
url = {https://journals.ametsoc.org/view/journals/clim/34/6/JCLI-D-20-0380.1.xml},
year = {2021},
date = {2021-01-01},
journal = {Journal of Climate},
volume = {34},
number = {6},
pages = {2189-2203},
abstract = {This study investigates the potential effects of historical deforestation in South America using a regional climate model driven with reanalysis data. Two different sources of data were used to quantify deforestation during the 1980s to 2010s, leading to two scenarios of forest loss: smaller but spatially continuous in scenario 1 and larger but spatially scattered in scenario 2. The model simulates a generally warmer and drier local climate following deforestation. Vegetation canopy becomes warmer due to reduced canopy evapotranspiration, and ground becomes warmer due to more radiation reaching the ground. The warming signal for surface air is weaker than for ground and vegetation, likely due to reduced surface roughness suppressing the sensible heat flux. For surface air over deforested areas, the warming signal is stronger for the nighttime minimum temperature and weaker or even becomes a cooling signal for the daytime maximum temperature, due to the strong radiative effects of albedo at midday, which reduces the diurnal amplitude of temperature. The drying signals over deforested areas include lower atmospheric humidity, less precipitation, and drier soil. The model identifies the La Plata basin as a region remotely influenced by deforestation, where a simulated increase of precipitation leads to wetter soil, higher ET, and a strong surface cooling. Over both deforested and remote areas, the deforestation-induced surface climate changes are much stronger in scenario 2 than scenario 1; coarse-resolution data and models (such as in scenario 1) cannot represent the detailed spatial structure of deforestation and underestimate its impact on local and regional climates.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study investigates the potential effects of historical deforestation in South America using a regional climate model driven with reanalysis data. Two different sources of data were used to quantify deforestation during the 1980s to 2010s, leading to two scenarios of forest loss: smaller but spatially continuous in scenario 1 and larger but spatially scattered in scenario 2. The model simulates a generally warmer and drier local climate following deforestation. Vegetation canopy becomes warmer due to reduced canopy evapotranspiration, and ground becomes warmer due to more radiation reaching the ground. The warming signal for surface air is weaker than for ground and vegetation, likely due to reduced surface roughness suppressing the sensible heat flux. For surface air over deforested areas, the warming signal is stronger for the nighttime minimum temperature and weaker or even becomes a cooling signal for the daytime maximum temperature, due to the strong radiative effects of albedo at midday, which reduces the diurnal amplitude of temperature. The drying signals over deforested areas include lower atmospheric humidity, less precipitation, and drier soil. The model identifies the La Plata basin as a region remotely influenced by deforestation, where a simulated increase of precipitation leads to wetter soil, higher ET, and a strong surface cooling. Over both deforested and remote areas, the deforestation-induced surface climate changes are much stronger in scenario 2 than scenario 1; coarse-resolution data and models (such as in scenario 1) cannot represent the detailed spatial structure of deforestation and underestimate its impact on local and regional climates.
Chakraborty, Sudip; Jiang, Jonathan H.; Su, Hui; Fu, Rong
On the role of aerosol radiative effect in the wet season onset timing over the Congo rainforest during boreal autumn Journal Article
In: Atmospheric Chemistry and Physics, vol. 21, pp. 12855–12866, 2021.
@article{2292,
title = {On the role of aerosol radiative effect in the wet season onset timing over the Congo rainforest during boreal autumn},
author = {Sudip Chakraborty and Jonathan H. Jiang and Hui Su and Rong Fu},
url = {https://acp.copernicus.org/articles/21/12855/2021/},
year = {2021},
date = {2021-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {21},
pages = {12855–12866},
abstract = {The boreal summer dry season length is reported to have been increasing in the last 3 decades over the Congo rainforest, which is the second-largest rainforest in the world. In some years, the wet season in boreal autumn starts early, while in others it arrives late. The mechanism behind such a change in the wet season onset date has not been investigated yet. Using multi-satellite data sets, we discover that the variation in aerosols in the dry season plays a major role in determining the subsequent wet season onset. Dry season aerosol optical depth (AOD) influences the strength of the southern African easterly jet (AEJ-S) and, thus, the onset of the wet season. Higher AOD associated with a higher dust mass flux reduces the net downward shortwave radiation and decreases the surface temperature over the Congo rainforest region, leading to a stronger meridional temperature gradient between the rainforest and the Kalahari Desert as early as in June. The latter, in turn, strengthens the AEJ-S, sets in an early and a stronger easterly flow, and leads to a stronger equatorward convergence and an early onset of the wet season in late August to early September. The mean AOD in the dry season over the region is strongly correlated (r=0.7) with the timing of the subsequent wet season onset. Conversely, in low AOD years, the onset of the wet season over the Congo basin is delayed to mid-October.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The boreal summer dry season length is reported to have been increasing in the last 3 decades over the Congo rainforest, which is the second-largest rainforest in the world. In some years, the wet season in boreal autumn starts early, while in others it arrives late. The mechanism behind such a change in the wet season onset date has not been investigated yet. Using multi-satellite data sets, we discover that the variation in aerosols in the dry season plays a major role in determining the subsequent wet season onset. Dry season aerosol optical depth (AOD) influences the strength of the southern African easterly jet (AEJ-S) and, thus, the onset of the wet season. Higher AOD associated with a higher dust mass flux reduces the net downward shortwave radiation and decreases the surface temperature over the Congo rainforest region, leading to a stronger meridional temperature gradient between the rainforest and the Kalahari Desert as early as in June. The latter, in turn, strengthens the AEJ-S, sets in an early and a stronger easterly flow, and leads to a stronger equatorward convergence and an early onset of the wet season in late August to early September. The mean AOD in the dry season over the region is strongly correlated (r=0.7) with the timing of the subsequent wet season onset. Conversely, in low AOD years, the onset of the wet season over the Congo basin is delayed to mid-October.
Worden, Sarah R.; Fu, Rong; Chakraborty, Sudip; Liu, Junjie; Worden, John
Where Does Moisture Come From Over the Congo Basin? Journal Article
In: Journal of Geophysical Research: Biogensciences, vol. 126, 2021.
@article{2284,
title = {Where Does Moisture Come From Over the Congo Basin?},
author = {Sarah R. Worden and Rong Fu and Sudip Chakraborty and Junjie Liu and John Worden},
url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020JG006024},
year = {2021},
date = {2021-01-01},
journal = {Journal of Geophysical Research: Biogensciences},
volume = {126},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Fu, Rong; Hoell, Andrew; Mankin, Justin; Sheffield, Amanda; Simpson, Isla
Tackling Challenges of a Drier, Hotter, More Fire-Prone Future Journal Article
In: EOS, vol. 102, 2021.
@article{2230,
title = {Tackling Challenges of a Drier, Hotter, More Fire-Prone Future},
author = {Rong Fu and Andrew Hoell and Justin Mankin and Amanda Sheffield and Isla Simpson},
url = {https://eos.org/opinions/tackling-challenges-of-a-drier-hotter-more-fire-prone-future},
year = {2021},
date = {2021-01-01},
journal = {EOS},
volume = {102},
abstract = {Research is increasingly showing how drought, heat, and wildfire influence each other. Ongoing collaborations provide templates for how best to study these phenomena and plan for their future impacts.},
keywords = {},
pubstate = {published},
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}
Research is increasingly showing how drought, heat, and wildfire influence each other. Ongoing collaborations provide templates for how best to study these phenomena and plan for their future impacts.
Wang, Gaoyun; Zhuang, Yizhou; Fu, Rong; Zhao, Siyu; Wang, Hongqing
Improving Seasonal Prediction of California Winter Precipitation Using Canonical Correlation Analysis Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 126, 2021.
@article{2062,
title = {Improving Seasonal Prediction of California Winter Precipitation Using Canonical Correlation Analysis},
author = {Gaoyun Wang and Yizhou Zhuang and Rong Fu and Siyu Zhao and Hongqing Wang},
year = {2021},
date = {2021-01-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {126},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Zhao, Siyu; Fu, Rong; Zhuang, Yizhou; Wang, Gaoyun
Long-Lead Seasonal Prediction of Streamflow over the Upper Colorado River Basin: The Role of the Pacific Sea Surface Temperature and Beyond Journal Article
In: Journal of Climate, vol. 34, no. 16, pp. 6855–6873, 2021.
@article{2061,
title = {Long-Lead Seasonal Prediction of Streamflow over the Upper Colorado River Basin: The Role of the Pacific Sea Surface Temperature and Beyond},
author = {Siyu Zhao and Rong Fu and Yizhou Zhuang and Gaoyun Wang},
url = {10.1175/JCLI-D-20-0824.1},
year = {2021},
date = {2021-01-01},
journal = {Journal of Climate},
volume = {34},
number = {16},
pages = {6855–6873},
abstract = {We have developed two statistical models for extended seasonal predictions of the upper Colorado River basin (UCRB) natural streamflow during April–July: a stepwise linear regression (reduced to a simple regression with one predictor) and a neural network model. Monthly, basin-averaged soil moisture, snow water equivalent (SWE), precipitation, and the Pacific sea surface temperature (SST) are selected as potential predictors. Pacific SST predictors (PSPs) are derived from a dipole pattern over the Pacific (30°S–65°N) that is correlated with the lagging streamflow. For both models, the correlation between the hindcasted and observed streamflow exceeds 0.60 for lead times less than 4 months using soil moisture, SWE, and precipitation as predictors. This correlation is higher than that of an autoregression model (correlation ~ 0.50). Since these land surface and atmospheric variables have no statistically significant correlations with the streamflow, PSPs are then incorporated into the models. The two models have a correlation of ~0.50 using PSPs alone for lead times from 6 to 9 months, and such skills are probably associated with stronger correlation between SST and streamflow in recent decades. The similar prediction skills between the two models suggest a largely linear system between SST and streamflow. Four predictors together can further improve short-lead prediction skills (correlation ~ 0.80). Therefore, our results confirm the advantage of the Pacific SST information in predicting the UCRB streamflow with a long lead time and can provide useful climate information for water supply planning and decisions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We have developed two statistical models for extended seasonal predictions of the upper Colorado River basin (UCRB) natural streamflow during April–July: a stepwise linear regression (reduced to a simple regression with one predictor) and a neural network model. Monthly, basin-averaged soil moisture, snow water equivalent (SWE), precipitation, and the Pacific sea surface temperature (SST) are selected as potential predictors. Pacific SST predictors (PSPs) are derived from a dipole pattern over the Pacific (30°S–65°N) that is correlated with the lagging streamflow. For both models, the correlation between the hindcasted and observed streamflow exceeds 0.60 for lead times less than 4 months using soil moisture, SWE, and precipitation as predictors. This correlation is higher than that of an autoregression model (correlation ~ 0.50). Since these land surface and atmospheric variables have no statistically significant correlations with the streamflow, PSPs are then incorporated into the models. The two models have a correlation of ~0.50 using PSPs alone for lead times from 6 to 9 months, and such skills are probably associated with stronger correlation between SST and streamflow in recent decades. The similar prediction skills between the two models suggest a largely linear system between SST and streamflow. Four predictors together can further improve short-lead prediction skills (correlation ~ 0.80). Therefore, our results confirm the advantage of the Pacific SST information in predicting the UCRB streamflow with a long lead time and can provide useful climate information for water supply planning and decisions.
Zhuang, Yizhou; Erfanian, Amir; Fu, Rong
Dryness over the US Southwest, a Springboard for Cold Season Pacific SST to Influence Warm Season Drought over the US Great Plains Journal Article
In: Journal of Hydrometeorology, vol. 22, no. 1, pp. 63-76, 2021.
@article{2032,
title = {Dryness over the US Southwest, a Springboard for Cold Season Pacific SST to Influence Warm Season Drought over the US Great Plains},
author = {Yizhou Zhuang and Amir Erfanian and Rong Fu},
year = {2021},
date = {2021-01-01},
journal = {Journal of Hydrometeorology},
volume = {22},
number = {1},
pages = {63-76},
abstract = {Although the influence of sea surface temperature (SST) forcing and large scale teleconnection on summer droughts over the United States (US) Great Plains has been suggested for decades, the underlying mechanisms are still not fully understood. Here we show a significant correlation between a low-level moisture condition over the US Southwest in spring and rainfall variability over the Great Plains in summer. Such a connection is due to the strong influence of the Southwest dryness on the zonal moisture advection to the Great Plains from spring to summer. This advection is an important contributor for the moisture deficit during spring to early summer, and so can initiate warm season drought over the Great Plains. In other words, the well documented influence of cold season Pacific SST on the Southwest rainfall in spring, and the influence of the latter on the zonal moisture advection to the Great Plains from spring to summer, allows the Pacific climate variability in winter and spring to explain over 35% of the variance of the summer precipitation over the Great Plains, more than that can be explained by the previous documented West Pacific-North America (WPNA) teleconnection forced by tropical Pacific SST in early summer. Thus, this remote land surface feedback due to the Southwest dryness can potentially improve the predictability of summer precipitation and drought onsets over the Great Plains.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Although the influence of sea surface temperature (SST) forcing and large scale teleconnection on summer droughts over the United States (US) Great Plains has been suggested for decades, the underlying mechanisms are still not fully understood. Here we show a significant correlation between a low-level moisture condition over the US Southwest in spring and rainfall variability over the Great Plains in summer. Such a connection is due to the strong influence of the Southwest dryness on the zonal moisture advection to the Great Plains from spring to summer. This advection is an important contributor for the moisture deficit during spring to early summer, and so can initiate warm season drought over the Great Plains. In other words, the well documented influence of cold season Pacific SST on the Southwest rainfall in spring, and the influence of the latter on the zonal moisture advection to the Great Plains from spring to summer, allows the Pacific climate variability in winter and spring to explain over 35% of the variance of the summer precipitation over the Great Plains, more than that can be explained by the previous documented West Pacific-North America (WPNA) teleconnection forced by tropical Pacific SST in early summer. Thus, this remote land surface feedback due to the Southwest dryness can potentially improve the predictability of summer precipitation and drought onsets over the Great Plains.
2020
Dai, Lan; Wright, Jonathon S.; Fu, Rong
Moisture and Energy Budget Perspectives on Summer Drought in North China Journal Article
In: Journal of Climate, vol. 33, no. 23, pp. 10149-10167, 2020.
@article{2274,
title = {Moisture and Energy Budget Perspectives on Summer Drought in North China},
author = {Lan Dai and Jonathon S. Wright and Rong Fu},
url = {https://journals.ametsoc.org/view/journals/clim/33/23/jcliD200176.xml},
year = {2020},
date = {2020-01-01},
journal = {Journal of Climate},
volume = {33},
number = {23},
pages = {10149-10167},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Madakumbura, G. D.; Goulden, M. L.; Hall, A.; Fu, R.; Moritz, M. A.; Koven, C. D.; Kueppers, L. M.; Norlen, C. A.; Randerson, J. T.
Recent California tree mortality portends future increase in drought-driven forest die-off Journal Article
In: Environmental Research Letters, vol. 15, 2020.
@article{2272,
title = {Recent California tree mortality portends future increase in drought-driven forest die-off},
author = {G. D. Madakumbura and M. L. Goulden and A. Hall and R. Fu and M. A. Moritz and C. D. Koven and L. M. Kueppers and C. A. Norlen and J. T. Randerson},
year = {2020},
date = {2020-01-01},
journal = {Environmental Research Letters},
volume = {15},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ren, Diandong; Fu, Rong; Dickinson, Robert E.; Leslie, Lance M.; Wang, Xingbao
Aviation Impacts on Fuel Efficiency of a Future More Viscous Atmosphere Journal Article
In: Bulletin of the American Meteorological Society, 2020.
@article{2118,
title = {Aviation Impacts on Fuel Efficiency of a Future More Viscous Atmosphere},
author = {Diandong Ren and Rong Fu and Robert E. Dickinson and Lance M. Leslie and Xingbao Wang},
year = {2020},
date = {2020-01-01},
journal = {Bulletin of the American Meteorological Society},
abstract = {Aircraft cruising near the tropopause currently benefit from the highest thermal efficiency and the least viscous (sticky) air, within the lowest 50 km of the Earth’s atmosphere. Both advantages wane in a warming climate, because atmospheric dynamic viscosity increases with temperature, in synergy with the simultaneous engine efficiency reduction. Here, skin friction drag, the dominant term for extra aviation fuel consumption in a future warming climate, is quantified by 34 climate models under a strong emissions scenario. Since 1950, the viscosity increase at cruising altitudes (~200 hPa) reaches ~1.5% per century, corresponding to a total drag increment of ~0.22% per century for commercial aircraft. Meridional gradients and regional disparities exist, with low-mid latitudes experiencing greater increases in skin friction drag. The North Atlantic Corridor (NAC) is moderately affected, but its high traffic volume generates additional fuel cost of ~3.8×107 gallons annually by 2100, compared to 2010. Globally, a normal year after 2100 would consume an extra ~4×106 barrels per year. Inter model spread is <5% of the ensemble mean, due to high inter-climate model consensus for warming trends at cruising altitudes in the tropics and subtropics. Because temperature is a well simulated parameter in the IPCC archive, with only a moderate inter-model spread, the conclusions drawn here are statistically robust. Notably, additional fuel costs are likely from the increased vertical shear and related turbulence at NAC cruising altitudes. Increased flight log availability is required to confirm this apparent increasing turbulence trend.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Aircraft cruising near the tropopause currently benefit from the highest thermal efficiency and the least viscous (sticky) air, within the lowest 50 km of the Earth’s atmosphere. Both advantages wane in a warming climate, because atmospheric dynamic viscosity increases with temperature, in synergy with the simultaneous engine efficiency reduction. Here, skin friction drag, the dominant term for extra aviation fuel consumption in a future warming climate, is quantified by 34 climate models under a strong emissions scenario. Since 1950, the viscosity increase at cruising altitudes (~200 hPa) reaches ~1.5% per century, corresponding to a total drag increment of ~0.22% per century for commercial aircraft. Meridional gradients and regional disparities exist, with low-mid latitudes experiencing greater increases in skin friction drag. The North Atlantic Corridor (NAC) is moderately affected, but its high traffic volume generates additional fuel cost of ~3.8×107 gallons annually by 2100, compared to 2010. Globally, a normal year after 2100 would consume an extra ~4×106 barrels per year. Inter model spread is <5% of the ensemble mean, due to high inter-climate model consensus for warming trends at cruising altitudes in the tropics and subtropics. Because temperature is a well simulated parameter in the IPCC archive, with only a moderate inter-model spread, the conclusions drawn here are statistically robust. Notably, additional fuel costs are likely from the increased vertical shear and related turbulence at NAC cruising altitudes. Increased flight log availability is required to confirm this apparent increasing turbulence trend.
Zhuang, Yizhou; Fu, Rong; Wang, Hongqing
Large-Scale Atmospheric Circulation Patterns Associated with US Great Plains Warm Season Droughts Revealed by Self-Organizing Maps Journal Article
In: Journal of Geophysical Research - Atmospheres, vol. 125, no. 5, 2020.
@article{2031,
title = {Large-Scale Atmospheric Circulation Patterns Associated with US Great Plains Warm Season Droughts Revealed by Self-Organizing Maps},
author = {Yizhou Zhuang and Rong Fu and Hongqing Wang},
year = {2020},
date = {2020-01-01},
journal = {Journal of Geophysical Research - Atmospheres},
volume = {125},
number = {5},
abstract = {This study uses a multivariate self-organizing map approach to diagnose precipitation anomalies over the United States’ Great Plains during the warm season (April–August) and the associated anomalous large-scale atmospheric patterns, as represented by standardized anomalies of 500 hPa geopotential (Z500'), integrated vapor transport (IVT'), and convective inhibition index (CINi'). Circulation patterns favoring dryness identified by the method are generally consistent with those shown in previous studies, but this study provides a more comprehensive and probabilistic characterization of those that favor drought over the Southern Great Plains (SGP) and the Central Great Plains (CGP) and their temporal evolutions. Six circulation types that are associated with warm season rainfall variability over the Great Plains are identified. The SGP droughts are attributable to more frequent and persistent northern low-southern high as well as dominant high circulation types and are connected to larger negative CINi'. In contrast, CGP droughts are attributable to more frequent and persistent western low-eastern high, or northern high-southern low, or dominant high patterns, and are linked to a larger negative IVT', but not larger CINi'. Thus, these results suggest that land surface dryness and a stable atmospheric boundary layer may play a more important role over the SGP than reduced moisture transport in warm season droughts, but reduced moisture transport may play a more important role than thermodynamic stability in droughts over the CGP.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study uses a multivariate self-organizing map approach to diagnose precipitation anomalies over the United States’ Great Plains during the warm season (April–August) and the associated anomalous large-scale atmospheric patterns, as represented by standardized anomalies of 500 hPa geopotential (Z500'), integrated vapor transport (IVT'), and convective inhibition index (CINi'). Circulation patterns favoring dryness identified by the method are generally consistent with those shown in previous studies, but this study provides a more comprehensive and probabilistic characterization of those that favor drought over the Southern Great Plains (SGP) and the Central Great Plains (CGP) and their temporal evolutions. Six circulation types that are associated with warm season rainfall variability over the Great Plains are identified. The SGP droughts are attributable to more frequent and persistent northern low-southern high as well as dominant high circulation types and are connected to larger negative CINi'. In contrast, CGP droughts are attributable to more frequent and persistent western low-eastern high, or northern high-southern low, or dominant high patterns, and are linked to a larger negative IVT', but not larger CINi'. Thus, these results suggest that land surface dryness and a stable atmospheric boundary layer may play a more important role over the SGP than reduced moisture transport in warm season droughts, but reduced moisture transport may play a more important role than thermodynamic stability in droughts over the CGP.
Chakraborty, Sudip; Jiang, Jonathan; Su, Hui; Fu, Rong
Deep Convective Evolution from Shallow Clouds over the Amazon and Congo Rainforests Journal Article
In: Journal of Geophysical Research - Atmospheres, vol. 125, no. 1, 2020.
@article{2007,
title = {Deep Convective Evolution from Shallow Clouds over the Amazon and Congo Rainforests},
author = {Sudip Chakraborty and Jonathan Jiang and Hui Su and Rong Fu},
year = {2020},
date = {2020-01-01},
journal = {Journal of Geophysical Research - Atmospheres},
volume = {125},
number = {1},
abstract = {Using satellite measurements from A-Train constellation and Global PrecipitationMeasurement mission, we investigate the relationships between the afternoon time shallow convectivetop height (CTHafternoon) and the evening time deep convective storm top height (CTHevening) and rain rate(RRevening) over the Amazon and Congo regions. We use CloudSat cloud type stratus and stratocumulus asthe shallow afternoon clouds. Our results indicate that the afternoon shallow clouds over the Congoregion are associated with suppressed and weakened evening time deep convection, whereas shallow cloudsover the Amazon region are associated with the growth of the evening time deep convection. Over the Congoregion, wefind that as CTHafternoonincreases, shallow convective rain rate in the afternoon (RRafternoon)increases. As a result, the evening time convective available potential energy (CAPE) as well as freetropospheric humidity (RH700-300) decrease. Consequently, condensation occurring inside deep convectionreduces and CTHeveningas well as RReveningdecrease over there. Over the Amazon region, however,RRafternoondoes not vary significantly with CTHafternoon. As CTHafternoonincreases, CAPE, RH700-300, andcondensation occurring inside deep convection increase in the evening. As a result, deep convectiveCTHeveningand RReveningincrease with CTHafternoonover the Amazon basin. These dissimilarities in theambient condition drive the shallow to deep convective evolution differently over these two rainforests.On the other hand, shallow clouds that remain shallow in the evening are associated with less CAPE andRH700-300,RRafternoon,and RRevening. Although CAPE and RH700-300promote deep convection to a heightcloud top height, high vertical wind shear inhibits deep convection.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Using satellite measurements from A-Train constellation and Global PrecipitationMeasurement mission, we investigate the relationships between the afternoon time shallow convectivetop height (CTHafternoon) and the evening time deep convective storm top height (CTHevening) and rain rate(RRevening) over the Amazon and Congo regions. We use CloudSat cloud type stratus and stratocumulus asthe shallow afternoon clouds. Our results indicate that the afternoon shallow clouds over the Congoregion are associated with suppressed and weakened evening time deep convection, whereas shallow cloudsover the Amazon region are associated with the growth of the evening time deep convection. Over the Congoregion, wefind that as CTHafternoonincreases, shallow convective rain rate in the afternoon (RRafternoon)increases. As a result, the evening time convective available potential energy (CAPE) as well as freetropospheric humidity (RH700-300) decrease. Consequently, condensation occurring inside deep convectionreduces and CTHeveningas well as RReveningdecrease over there. Over the Amazon region, however,RRafternoondoes not vary significantly with CTHafternoon. As CTHafternoonincreases, CAPE, RH700-300, andcondensation occurring inside deep convection increase in the evening. As a result, deep convectiveCTHeveningand RReveningincrease with CTHafternoonover the Amazon basin. These dissimilarities in theambient condition drive the shallow to deep convective evolution differently over these two rainforests.On the other hand, shallow clouds that remain shallow in the evening are associated with less CAPE andRH700-300,RRafternoon,and RRevening. Although CAPE and RH700-300promote deep convection to a heightcloud top height, high vertical wind shear inhibits deep convection.
Grimm, A. M.; Dominguez, F.; Cavalcanti, I. F. A.; Cavazos, T.; Gan, M. A.; Dias, P. L. Silva; Fu, R.; Castro, C.; Hu, H.; Barreiro, M.
South and North American Monsoons: characteristics, life cycle, variability, modelling and prediction Book Chapter
In: The Multi-scale Global Monsoon System, 2020.
@inbook{1981,
title = {South and North American Monsoons: characteristics, life cycle, variability, modelling and prediction},
author = {A. M. Grimm and F. Dominguez and I. F. A. Cavalcanti and T. Cavazos and M. A. Gan and P. L. Silva Dias and R. Fu and C. Castro and H. Hu and M. Barreiro},
url = {https://www.worldscientific.com/worldscibooks/10.1142/11723},
year = {2020},
date = {2020-01-01},
booktitle = {The Multi-scale Global Monsoon System},
keywords = {},
pubstate = {published},
tppubtype = {inbook}
}
2019
Fernando, D. Nelun; Chakraborty, Sudip; Fu, Rong; Mace, Robert E.
A process-based statistical seasonal prediction of May–July rainfall anomalies over Texas and the Southern Great Plains of the United States Journal Article
In: Climate Services, 2019.
@article{1996,
title = {A process-based statistical seasonal prediction of May-July rainfall anomalies over Texas and the Southern Great Plains of the United States},
author = {D. Nelun Fernando and Sudip Chakraborty and Rong Fu and Robert E. Mace},
year = {2019},
date = {2019-01-01},
journal = {Climate Services},
abstract = {With the aim of providing actionable drought early warning information that water managers and reservoir oper- ators in Texas could use to implement drought contingency triggers on water supply sources, we have developed a statistical seasonal prediction system using a canonical correlation analysis prediction model to predict rainfall from May through July (MJJ), the main rainfall season over much of Texas and the Southern Great Plains. The statistical model is trained with data between 1982 and 2005 using standardized anomalous geopotential height at 500 hPa, convective inhibition energy, and soil moisture content in April as the predictors to generate tercile categorical forecasts of MJJ rainfall. Based on commonly used forecast skill metrics, this statistical prediction sys- tem provides 20–60% higher skill than that obtained from dynamical seasonal forecasts, and the exceeds skill due to the persistence of MJJ rainfall anomalies over Texas, western Louisiana, Oklahoma and the Southern Kansas. 2011 hindcast shows that below-normal MJJ rainfall anomalies comparable to those observed over most of the region. The forecasts for 2014 captured the above-normal MJJ rainfall anomalies as observed in that year. The forecasts since 2014 have shown acceptable prediction skills at one-to-three months’ lead-time. We have also ex- tended the lead-time to generate probabilistic MJJ rainfall forecasts from January through March using a hybrid dynamical-statistical forecast scheme. The predictions have been used by the Texas Water Development Board to inform the Texas State Drought Preparedness Council and to support the implementation of drought contingency triggers for water supply sources by stakeholders, such as river authorities.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
With the aim of providing actionable drought early warning information that water managers and reservoir oper- ators in Texas could use to implement drought contingency triggers on water supply sources, we have developed a statistical seasonal prediction system using a canonical correlation analysis prediction model to predict rainfall from May through July (MJJ), the main rainfall season over much of Texas and the Southern Great Plains. The statistical model is trained with data between 1982 and 2005 using standardized anomalous geopotential height at 500 hPa, convective inhibition energy, and soil moisture content in April as the predictors to generate tercile categorical forecasts of MJJ rainfall. Based on commonly used forecast skill metrics, this statistical prediction sys- tem provides 20–60% higher skill than that obtained from dynamical seasonal forecasts, and the exceeds skill due to the persistence of MJJ rainfall anomalies over Texas, western Louisiana, Oklahoma and the Southern Kansas. 2011 hindcast shows that below-normal MJJ rainfall anomalies comparable to those observed over most of the region. The forecasts for 2014 captured the above-normal MJJ rainfall anomalies as observed in that year. The forecasts since 2014 have shown acceptable prediction skills at one-to-three months’ lead-time. We have also ex- tended the lead-time to generate probabilistic MJJ rainfall forecasts from January through March using a hybrid dynamical-statistical forecast scheme. The predictions have been used by the Texas Water Development Board to inform the Texas State Drought Preparedness Council and to support the implementation of drought contingency triggers for water supply sources by stakeholders, such as river authorities.
Costa, M. H.; Fleck, L. C.; Cohn, A. S.; Abrahão, G. M.; Brando, P. M.; Coe, M. T.; Fu, R.; Lawrence, D.; Pires, G. F.; Pousa, R.; Soares-Filho, B. S.
Climate risks to Amazon agriculture raise awareness to conserve local forests Journal Article
In: Frontier of Ecology and the environment, vol. 17, no. 10, pp. 584-590, 2019.
@article{1980,
title = {Climate risks to Amazon agriculture raise awareness to conserve local forests},
author = {M. H. Costa and L. C. Fleck and A. S. Cohn and G. M. Abrahão and P. M. Brando and M. T. Coe and R. Fu and D. Lawrence and G. F. Pires and R. Pousa and B. S. Soares-Filho},
year = {2019},
date = {2019-01-01},
journal = {Frontier of Ecology and the environment},
volume = {17},
number = {10},
pages = {584-590},
abstract = {In southern Amazonia, more than half of all cropland is devoted to the production of two rainfed crops per year, an agricultural practice known as “double cropping” (DC). Climate change, including feedbacks between changes in land use and the local cli-mate, is shortening the extent of the historical rainy season in southern Amazonia, increasing the risk of future detrimental envi-ronmental conditions, and posing a threat to the intensive DC agriculture that is currently practiced in that region, with potential negative consequences at regional, national, and even global scales. We argue that the conservation of undeveloped forests and savannas in southern Amazonia is supported by socioeconomic justifications and is in the best interests of agribusiness, local gov-ernments, and the public.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In southern Amazonia, more than half of all cropland is devoted to the production of two rainfed crops per year, an agricultural practice known as “double cropping” (DC). Climate change, including feedbacks between changes in land use and the local cli-mate, is shortening the extent of the historical rainy season in southern Amazonia, increasing the risk of future detrimental envi-ronmental conditions, and posing a threat to the intensive DC agriculture that is currently practiced in that region, with potential negative consequences at regional, national, and even global scales. We argue that the conservation of undeveloped forests and savannas in southern Amazonia is supported by socioeconomic justifications and is in the best interests of agribusiness, local gov-ernments, and the public.
Shi, M. J.; Liu, J. J.; Woden, J. R.; Bloom, A. A.; Wong, S.; Fu, R.
The 2005 Amazon Drought Legacy Effect Delayed the 2006 Wet Season Onset Journal Article
In: Geophysical Research Letters banner, vol. 46, pp. 9082-9090, 2019.
@article{1979,
title = {The 2005 Amazon Drought Legacy Effect Delayed the 2006 Wet Season Onset},
author = {M. J. Shi and J. J. Liu and J. R. Woden and A. A. Bloom and S. Wong and R. Fu},
year = {2019},
date = {2019-01-01},
journal = {Geophysical Research Letters banner},
volume = {46},
pages = {9082-9090},
abstract = {While the long-term drought effect on tropical forests has been observed in ground-based and remote sensing measurements, the feedback of reduced forest biomass on subsequent rainfall is not well understood. We evaluate the impact of slow forest recovery after the 2005 Amazonian drought on local evapotranspiration (ET) and wet season onset (WSO) using remotely sensed precipitation, deuterium retrievals, reanalysis data, and a new ET product. A comparison to the 2009 rainy season, which exhibits similar large-scale moisture flux convergence, shows that 2006 experienced a 25% ET reduction and 20 days of postponed WSO in the dry-to-wet transition. Our results imply that ET reduction due to drought-driven legacy effect on the Amazon rainforest could be a crucial factor triggering WSO delay in the transitional season following drought events.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
While the long-term drought effect on tropical forests has been observed in ground-based and remote sensing measurements, the feedback of reduced forest biomass on subsequent rainfall is not well understood. We evaluate the impact of slow forest recovery after the 2005 Amazonian drought on local evapotranspiration (ET) and wet season onset (WSO) using remotely sensed precipitation, deuterium retrievals, reanalysis data, and a new ET product. A comparison to the 2009 rainy season, which exhibits similar large-scale moisture flux convergence, shows that 2006 experienced a 25% ET reduction and 20 days of postponed WSO in the dry-to-wet transition. Our results imply that ET reduction due to drought-driven legacy effect on the Amazon rainforest could be a crucial factor triggering WSO delay in the transitional season following drought events.
Gentine, P.; Massmann, A.; Lintner, B. R.; Alemohammad, S. H.; Fu, R.; Green, J. K.; Kennedy, D.; Arellano, J. V. G.
Land-atmospheric Interactions in the tropics - a review Journal Article
In: Hydrology and Earth System Sciences, vol. 23, pp. 4171–4197, 2019.
@article{1978,
title = {Land-atmospheric Interactions in the tropics - a review},
author = {P. Gentine and A. Massmann and B. R. Lintner and S. H. Alemohammad and R. Fu and J. K. Green and D. Kennedy and J. V. G. Arellano},
year = {2019},
date = {2019-01-01},
journal = {Hydrology and Earth System Sciences},
volume = {23},
pages = {4171–4197},
abstract = {The continental tropics play a leading role in the terrestrial water and carbon cycles. Land–atmosphere interactions are integral in the regulation of surface energy, water and carbon fluxes across multiple spatial and temporal scales over tropical continents. We review here some of the important characteristics of tropical continental climates and how land–atmosphere interactions regulate them. Along with a wide range of climates, the tropics manifest a diverse array of land–atmosphere interactions. Broadly speaking, in tropical rainforests, light and energy are typically more limiting than precipitation and water supply for photosynthesis and evapotranspiration; whereas in savanna and semi-arid regions water is the critical regulator of surface fluxes and land–atmosphere interactions. We discuss the impact of the land surface, how it affects shallow clouds and how these clouds can feedback to the surface by modulating surface radiation. Some results from recent research suggest that shallow clouds may be especially critical to land–atmosphere interactions as these regulate the energy budget and moisture transport to the lower troposphere, which in turn affects deep convection. On the other hand, the impact of land surface conditions on deep convection appear to occur over larger, non-local, scales and might be critically affected by transitional regions between the climatologically dry and wet tropics.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The continental tropics play a leading role in the terrestrial water and carbon cycles. Land–atmosphere interactions are integral in the regulation of surface energy, water and carbon fluxes across multiple spatial and temporal scales over tropical continents. We review here some of the important characteristics of tropical continental climates and how land–atmosphere interactions regulate them. Along with a wide range of climates, the tropics manifest a diverse array of land–atmosphere interactions. Broadly speaking, in tropical rainforests, light and energy are typically more limiting than precipitation and water supply for photosynthesis and evapotranspiration; whereas in savanna and semi-arid regions water is the critical regulator of surface fluxes and land–atmosphere interactions. We discuss the impact of the land surface, how it affects shallow clouds and how these clouds can feedback to the surface by modulating surface radiation. Some results from recent research suggest that shallow clouds may be especially critical to land–atmosphere interactions as these regulate the energy budget and moisture transport to the lower troposphere, which in turn affects deep convection. On the other hand, the impact of land surface conditions on deep convection appear to occur over larger, non-local, scales and might be critically affected by transitional regions between the climatologically dry and wet tropics.
Leite-Filho, A. T.; Costa, M. H.; Fu, R.
The southern Amazon rainy season: the role of deforestation and its interactions with large-scale mechanisms Journal Article
In: International J. of Climatology, 2019.
@article{1977,
title = {The southern Amazon rainy season: the role of deforestation and its interactions with large-scale mechanisms},
author = {A. T. Leite-Filho and M. H. Costa and R. Fu},
url = {https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/joc.6335},
year = {2019},
date = {2019-01-01},
journal = {International J. of Climatology},
abstract = {Past studies presented evidence that deforestation may affect the precipitation seasonality in southern Amazon. This study uses daily rainfall data from TRMM 3B42 product and a recent yearly 1-km land use dataset to evaluate the quantitative effects of deforestation on the onset, demise and length of the rainy season in Southern Amazon for a period of 15 years (1998-2012). Additionally, we use the Niño4 index, zonal wind data and deforestation data to explain and predict the interannual variability of the onset of the rainy season. During this period, onset has delayed ~0.38±0.05 days per year (5.7±0.75 days in 15 years), demise has advanced 1.34±0.76 days per year (20±11.4 days in 15 years) and the rainy season has shortened by 1.81±0.97 days per year (27±14.5 days in 15 years). Onset, demise and length also present meridional and zonal gradients linked to large-scale climate mechanisms. After removing the effects related to geographical position and year, we verified a relationship between onset, demise and length and deforestation: Onset delays ~0.4±0.12 day, demise advances ~1.0±0.22 day and length decreases ~0.9±0.34 day per each 10% deforestation increase relative to existing forested area. We also present empirical evidence of the interaction between large-scale and local scale processes, with interannual variation of the onset in the region explained by Niño4 sea surface temperature anomalies, Southern Hemisphere subtropical jet position, deforestation and their interactions (r2 = 69%, p < 0.001, MAE = 2.7 days).},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Past studies presented evidence that deforestation may affect the precipitation seasonality in southern Amazon. This study uses daily rainfall data from TRMM 3B42 product and a recent yearly 1-km land use dataset to evaluate the quantitative effects of deforestation on the onset, demise and length of the rainy season in Southern Amazon for a period of 15 years (1998-2012). Additionally, we use the Niño4 index, zonal wind data and deforestation data to explain and predict the interannual variability of the onset of the rainy season. During this period, onset has delayed ~0.38±0.05 days per year (5.7±0.75 days in 15 years), demise has advanced 1.34±0.76 days per year (20±11.4 days in 15 years) and the rainy season has shortened by 1.81±0.97 days per year (27±14.5 days in 15 years). Onset, demise and length also present meridional and zonal gradients linked to large-scale climate mechanisms. After removing the effects related to geographical position and year, we verified a relationship between onset, demise and length and deforestation: Onset delays ~0.4±0.12 day, demise advances ~1.0±0.22 day and length decreases ~0.9±0.34 day per each 10% deforestation increase relative to existing forested area. We also present empirical evidence of the interaction between large-scale and local scale processes, with interannual variation of the onset in the region explained by Niño4 sea surface temperature anomalies, Southern Hemisphere subtropical jet position, deforestation and their interactions (r2 = 69%, p < 0.001, MAE = 2.7 days).
Erfanian, Amir; Fu, Rong
The role of spring dry zonal advection in summer drought onset over the US Great Plains Journal Article
In: Atmospheric Chemistry and Physics, no. 19, pp. 15199–15216, 2019.
@article{1946,
title = {The role of spring dry zonal advection in summer drought onset over the US Great Plains},
author = {Amir Erfanian and Rong Fu},
year = {2019},
date = {2019-01-01},
journal = {Atmospheric Chemistry and Physics},
number = {19},
pages = {15199–15216},
abstract = {This study addresses the role of the atmospheric moisture budget in determining the onset and development of summer droughts over the North American Great Plains (GP) using two state-of-the-art reanalysis datasets. We identified zonal moisture advection as the main cause of severe tropospheric drying during the extreme droughts in the southern GP in 2011 and northern GP in 2012. For both events, the eastward advection of anomalously dry and warm air in the free troposphere in spring set the stage for summer drought. This led to a sharp drop in relative humidity above the boundary layer, enhancing dry entrainment and suppressing deep convection. Further breakdown of the zonal advection into dynamic (caused by circulation anomalies) and thermodynamic (caused by moisture anomalies) contributions reveals dominance of thermodynamic advection in the tropospheric drying observed during the onset of both 2011 and 2012 droughts. The dependence of thermodynamic advection on the moisture gradient links springtime precipitation in the Rockies and southwestern US, the source region of the anomalous dry advection, to the GP summer precipitation (with correlations > 0.4 using gauge-based data). Identifying this previously overlooked precursor of the GP summer droughts improves our predictive understanding of drought onset mechanisms over the region.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study addresses the role of the atmospheric moisture budget in determining the onset and development of summer droughts over the North American Great Plains (GP) using two state-of-the-art reanalysis datasets. We identified zonal moisture advection as the main cause of severe tropospheric drying during the extreme droughts in the southern GP in 2011 and northern GP in 2012. For both events, the eastward advection of anomalously dry and warm air in the free troposphere in spring set the stage for summer drought. This led to a sharp drop in relative humidity above the boundary layer, enhancing dry entrainment and suppressing deep convection. Further breakdown of the zonal advection into dynamic (caused by circulation anomalies) and thermodynamic (caused by moisture anomalies) contributions reveals dominance of thermodynamic advection in the tropospheric drying observed during the onset of both 2011 and 2012 droughts. The dependence of thermodynamic advection on the moisture gradient links springtime precipitation in the Rockies and southwestern US, the source region of the anomalous dry advection, to the GP summer precipitation (with correlations > 0.4 using gauge-based data). Identifying this previously overlooked precursor of the GP summer droughts improves our predictive understanding of drought onset mechanisms over the region.
2018
Chakraborty, S.; Schiro, K. A.; Fu, R.; Neelin, J. D.
On the role of aerosols, humidity, and vertical wind shear in the transition of shallow to deep convection at the Green Ocean Amazon 2014/5 site Journal Article
In: Atmospheric Chemistry and Physics, vol. 18, pp. 11135-11148, 2018.
@article{1356,
title = {On the role of aerosols, humidity, and vertical wind shear in the transition of shallow to deep convection at the Green Ocean Amazon 2014/5 site},
author = {S. Chakraborty and K. A. Schiro and R. Fu and J. D. Neelin},
year = {2018},
date = {2018-03-01},
journal = {Atmospheric Chemistry and Physics},
volume = {18},
pages = {11135-11148},
abstract = {The preconditioning of the atmosphere for a shallow-to-deep convective transition during the dry-to-wet season transition period (August–November) is investigated using Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign data from March 2014 to November 2015 in Manacapuru, Brazil. In comparison to conditions observed prior to shallow convection, anomalously high humidity in the free troposphere and boundary layer is observed prior to a shallow-to-deep convection transition. An entraining plume model, which captures this leading dependence on lower tropospheric moisture, is employed to study indirect thermodynamic effects associated with vertical wind shear (VWS) and cloud condensation nuclei (CCN) concentration on preconvective conditions. The shallow-to-deep convective transition primarily depends on humidity, especially that from the free troposphere, which tends to increase plume buoyancy. Conditions preceding deep convection are associated with high relative humidity, and low-to-moderate CCN concentration (less than the 67th percentile, 1274 cm-3 ). VWS, however, shows little relation to moisture and plume buoyancy. Buoyancy estimates suggest that the latent heat release due to freezing is important to deep convective growth under all conditions analyzed, consistent with potential pathways for aerosol effects, even in the presence of a strong entrainment. Shallow-only convective growth, however, shows an association with a strong (weak) low (deep) level VWS and with higher CCN concentration.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The preconditioning of the atmosphere for a shallow-to-deep convective transition during the dry-to-wet season transition period (August–November) is investigated using Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign data from March 2014 to November 2015 in Manacapuru, Brazil. In comparison to conditions observed prior to shallow convection, anomalously high humidity in the free troposphere and boundary layer is observed prior to a shallow-to-deep convection transition. An entraining plume model, which captures this leading dependence on lower tropospheric moisture, is employed to study indirect thermodynamic effects associated with vertical wind shear (VWS) and cloud condensation nuclei (CCN) concentration on preconvective conditions. The shallow-to-deep convective transition primarily depends on humidity, especially that from the free troposphere, which tends to increase plume buoyancy. Conditions preceding deep convection are associated with high relative humidity, and low-to-moderate CCN concentration (less than the 67th percentile, 1274 cm-3 ). VWS, however, shows little relation to moisture and plume buoyancy. Buoyancy estimates suggest that the latent heat release due to freezing is important to deep convective growth under all conditions analyzed, consistent with potential pathways for aerosol effects, even in the presence of a strong entrainment. Shallow-only convective growth, however, shows an association with a strong (weak) low (deep) level VWS and with higher CCN concentration.
Chakraborty, Sudip; Fu, Rong; Rosenfeld, D.; Massie, Steven T
The influence of aerosols and meteorological conditions on the total rain volume Journal Article
In: Geophysical Research Letter, vol. 45, no. 23, pp. 13009-13106, 2018.
@article{1782,
title = {The influence of aerosols and meteorological conditions on the total rain volume},
author = {Sudip Chakraborty and Rong Fu and D. Rosenfeld and Steven T Massie},
year = {2018},
date = {2018-01-01},
journal = {Geophysical Research Letter},
volume = {45},
number = {23},
pages = {13009-13106},
abstract = {This study provides an observational assessment of the variations of the total rain volume (TRV) with aerosols through the entire lifetime of mesoscale convective systems (MCSs) over tropics. Using 70,000 MCSs’ samples, we show that TRV increases with aerosols from clean to moderately heavy polluted conditions (aerosol optical depth [AOD] similar to 0.0-0.4). TRV decreases when AOD exceeds 0.5. The TRV change with AOD is strongest under favorable meteorological conditions, such as high total precipitable water (45-75 kg/m(2)), high convective available potential energy (1,200-2,400 J/kg), and intermediate vertical wind shear (9-21 x 10(-4)/s). TRV of MCSs increases from 2 to 4 km(3) (rain depth similar to 20-40 mm) when AOD < 0.15 or > 0.5, to more than 12 km(3) (similar to 120 mm) when 0.2 < AOD < 0.4 under above the mentioned optimal meteorological conditions. The basic response of TRV to aerosol concentrations is similar under all the meteorological conditions and during all stages of the MCS lifecycle.Plain language summary Mesoscale convective systems (MCSs) contribute to the largest fraction of global rainfall and are often responsible for devastating flood events. It has long been hypothesized that aerosols can enhance rainfall of MCSs by suppressing rainfall during the early stage of the convection, enabling more cloud droplets to rise to higher altitude and so freeze. Freezing releases more latent heat, which drives strong rising motion and so enables formation of large hydrometeors for heavy rainfall. Thus, it is central to evaluate rainfall changes with aerosols through the entire lifetime of the MCCs. This work provides a first observational assessment of the variation of the total rain generated by MCSs through their lifetime with ambient aerosols, under various ambient meteorological conditions over the global tropical continents. Our results show that aerosols have a strong invigoration effect on MCSs’ total rainfall volume. Total rainfall volume increases as AOD increases up to 0.4 and decreases as AOD increases beyond 0.5. Such effects are similar throughout different phases of their convective lifecycle and under various meteorological conditions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study provides an observational assessment of the variations of the total rain volume (TRV) with aerosols through the entire lifetime of mesoscale convective systems (MCSs) over tropics. Using 70,000 MCSs’ samples, we show that TRV increases with aerosols from clean to moderately heavy polluted conditions (aerosol optical depth [AOD] similar to 0.0-0.4). TRV decreases when AOD exceeds 0.5. The TRV change with AOD is strongest under favorable meteorological conditions, such as high total precipitable water (45-75 kg/m(2)), high convective available potential energy (1,200-2,400 J/kg), and intermediate vertical wind shear (9-21 x 10(-4)/s). TRV of MCSs increases from 2 to 4 km(3) (rain depth similar to 20-40 mm) when AOD < 0.15 or > 0.5, to more than 12 km(3) (similar to 120 mm) when 0.2 < AOD < 0.4 under above the mentioned optimal meteorological conditions. The basic response of TRV to aerosol concentrations is similar under all the meteorological conditions and during all stages of the MCS lifecycle.Plain language summary Mesoscale convective systems (MCSs) contribute to the largest fraction of global rainfall and are often responsible for devastating flood events. It has long been hypothesized that aerosols can enhance rainfall of MCSs by suppressing rainfall during the early stage of the convection, enabling more cloud droplets to rise to higher altitude and so freeze. Freezing releases more latent heat, which drives strong rising motion and so enables formation of large hydrometeors for heavy rainfall. Thus, it is central to evaluate rainfall changes with aerosols through the entire lifetime of the MCCs. This work provides a first observational assessment of the variation of the total rain generated by MCSs through their lifetime with ambient aerosols, under various ambient meteorological conditions over the global tropical continents. Our results show that aerosols have a strong invigoration effect on MCSs’ total rainfall volume. Total rainfall volume increases as AOD increases up to 0.4 and decreases as AOD increases beyond 0.5. Such effects are similar throughout different phases of their convective lifecycle and under various meteorological conditions.
Ren, Diandong; Dickinson, Robert E.; Fu, Rong; Bornman, Janet F.; Guo, Weidong; Yang, Song
Impacts of climate warming on maximum aviation payloads Journal Article
In: Climate Dynamics, 2018.
@article{1655,
title = {Impacts of climate warming on maximum aviation payloads},
author = {Diandong Ren and Robert E. Dickinson and Rong Fu and Janet F. Bornman and Weidong Guo and Song Yang},
year = {2018},
date = {2018-01-01},
journal = {Climate Dynamics},
abstract = {The increasing importance of aviation activities in modern life coincides with a steady warming climate. However, the effect of climate warming on maximum aircraft carrying capacity or payload has been unclear. Here we clarify this issue using primary atmospheric parameters from 27 fully coupled climate models from the Coupled Model Inter-comparison Project 5 (CMIP5) archive, utilizing the direct proportionality of near-surface air density (NSAD) to maximum take-off total weight (MTOW). Historical (twentieth century) runs of these climate models showed high credibility in reproducing the reanalysis period (1950–2015) of NSAD. In particular, the model simulated trends in NSAD are highly aligned with the reanalysis values. This reduction in NSAD is a first order global signal, just as is the warming itself, that continues into the future. To examine the statistical significance of the density reduction, a t-test was performed for two 20-year periods 75 years apart (2080–2100 vs. 2005–2025), using the Representative Concentration Pathways (RCP) 8.5 emission scenario of the Intergovernmental Panel on Climate Change (IPCC). Most continental areas easily passed the test at a P-value of 0.05. These future changes of NSAD will likely have significant economic impacts on the aviation industry. For these two 20-year periods that we examined, the most extreme changes are in the Northern hemisphere in high latitudes, i.e., a 5% decrease in MTOW, or ~8.5–19% (aircraft-dependent) reduction in payload. The global average change is about 1%. For the busy North Atlantic Corridor (NAC), the reduction in MTOW is generally greater than 1% and that of payload several times larger.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The increasing importance of aviation activities in modern life coincides with a steady warming climate. However, the effect of climate warming on maximum aircraft carrying capacity or payload has been unclear. Here we clarify this issue using primary atmospheric parameters from 27 fully coupled climate models from the Coupled Model Inter-comparison Project 5 (CMIP5) archive, utilizing the direct proportionality of near-surface air density (NSAD) to maximum take-off total weight (MTOW). Historical (twentieth century) runs of these climate models showed high credibility in reproducing the reanalysis period (1950–2015) of NSAD. In particular, the model simulated trends in NSAD are highly aligned with the reanalysis values. This reduction in NSAD is a first order global signal, just as is the warming itself, that continues into the future. To examine the statistical significance of the density reduction, a t-test was performed for two 20-year periods 75 years apart (2080–2100 vs. 2005–2025), using the Representative Concentration Pathways (RCP) 8.5 emission scenario of the Intergovernmental Panel on Climate Change (IPCC). Most continental areas easily passed the test at a P-value of 0.05. These future changes of NSAD will likely have significant economic impacts on the aviation industry. For these two 20-year periods that we examined, the most extreme changes are in the Northern hemisphere in high latitudes, i.e., a 5% decrease in MTOW, or ~8.5–19% (aircraft-dependent) reduction in payload. The global average change is about 1%. For the busy North Atlantic Corridor (NAC), the reduction in MTOW is generally greater than 1% and that of payload several times larger.
Zhao, B.; Liou, K. N.; Gu, Y.; Jiang, J. H.; Li, Q. B.; Fu, R.; Huang, L.; Liu, X. H.; Shi, X. J.; Su, H.; He, C. L.
Impact of aerosols on ice crystal size Journal Article
In: Atmospheric Chemistry and Physics, vol. 18, no. 2, pp. 1065-1078, 2018.
@article{722,
title = {Impact of aerosols on ice crystal size},
author = {B. Zhao and K. N. Liou and Y. Gu and J. H. Jiang and Q. B. Li and R. Fu and L. Huang and X. H. Liu and X. J. Shi and H. Su and C. L. He},
year = {2018},
date = {2018-01-01},
journal = {Atmospheric Chemistry and Physics},
volume = {18},
number = {2},
pages = {1065-1078},
abstract = {The interactions between aerosols and ice clouds represent one of the largest uncertainties in global radiative forcing from pre-industrial time to the present. In particular, the impact of aerosols on ice crystal effective radius (Rei), which is a key parameter determining ice clouds’ net radiative effect, is highly uncertain due to limited and conflicting observational evidence. Here we investigate the effects of aerosols on Rei under different meteorological conditions using 9-year satellite observations. We find that the responses of Rei to aerosol loadings are modulated by water vapor amount in conjunction with several other meteorological parameters. While there is a significant negative correlation between Rei and aerosol loading in moist conditions, consistent with the “Twomey effect” for liquid clouds, a strong positive correlation between the two occurs in dry conditions. Simulations based on a cloud parcel model suggest that water vapor modulates the relative importance of different ice nucleation modes, leading to the opposite aerosol impacts between moist and dry conditions. When ice clouds are decomposed into those generated from deep convection and formed in situ, the water vapor modulation remains in effect for both ice cloud types, although the sensitivities of Rei to aerosols differ noticeably between them due to distinct formation mechanisms. The water vapor modulation can largely explain the difference in the responses of Rei to aerosol loadings in various seasons. A proper representation of the water vapor modulation is essential for an accurate estimate of aerosol–cloud radiative forcing produced by ice clouds.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The interactions between aerosols and ice clouds represent one of the largest uncertainties in global radiative forcing from pre-industrial time to the present. In particular, the impact of aerosols on ice crystal effective radius (Rei), which is a key parameter determining ice clouds’ net radiative effect, is highly uncertain due to limited and conflicting observational evidence. Here we investigate the effects of aerosols on Rei under different meteorological conditions using 9-year satellite observations. We find that the responses of Rei to aerosol loadings are modulated by water vapor amount in conjunction with several other meteorological parameters. While there is a significant negative correlation between Rei and aerosol loading in moist conditions, consistent with the “Twomey effect” for liquid clouds, a strong positive correlation between the two occurs in dry conditions. Simulations based on a cloud parcel model suggest that water vapor modulates the relative importance of different ice nucleation modes, leading to the opposite aerosol impacts between moist and dry conditions. When ice clouds are decomposed into those generated from deep convection and formed in situ, the water vapor modulation remains in effect for both ice cloud types, although the sensitivities of Rei to aerosols differ noticeably between them due to distinct formation mechanisms. The water vapor modulation can largely explain the difference in the responses of Rei to aerosol loadings in various seasons. A proper representation of the water vapor modulation is essential for an accurate estimate of aerosol–cloud radiative forcing produced by ice clouds.
2017
Bowerman, A. R.; Fu, R.; Yin, L.; Fernando, D. N.; Arias, P. A.; Dickinson, R. E.
An influence of extreme southern hemispheric cold surges on the North Atlantic Subtropical High through a shallow atmospheric circulation Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 122, 2017.
@article{723,
title = {An influence of extreme southern hemispheric cold surges on the North Atlantic Subtropical High through a shallow atmospheric circulation},
author = {A. R. Bowerman and R. Fu and L. Yin and D. N. Fernando and P. A. Arias and R. E. Dickinson},
year = {2017},
date = {2017-10-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {122},
abstract = {Previous studies have attributed interhemisphere influences of the atmosphere to the latitudinal propagation of planetary waves crossing the equator, to the triggering of equatorial Kelvin waves, or to monsoonal circulation. Over the American-Atlantic sector, such cross-equatorial influences rarely occur during boreal summer due to unfavorable atmospheric conditions. We have observed that an alternative mechanism provides an interhemisphere influence. When episodes of extreme cold surges and upper tropospheric westerly winds occur concurrently over southern hemisphere Amazonia, cold surges from extratropical South America can penetrate deep into southern Amazonia. Although they do not appear to influence upper tropospheric circulation of the northern hemisphere, extremely strong southerly cross-equatorial advection (>2σ standard deviations, or 2) of cold and dense air in the lower troposphere can reach as least 10°N. Such cold advection increases the northward cross-equatorial pressure gradient in the lower to middle troposphere, thus shallow northerly return flow below 500 hPa. This return flow and the strong lower tropospheric southerly cross-equatorial flow form an anomalous shallow meridional circulation spanning from southern Amazonia to the subtropical North Atlantic, with increased geopotential height anomalies exceeding +1σ to at least 18°N. It projects onto the southern edge of the North Atlantic Subtropical High (NASH), increasing its pressure and leading to equatorward expansion of NASH’s southern boundary. These anomalies enhance the NASH, leading to its equatorward expansion. These extreme cold surges can potentially improving the predictability of weather patterns of the tropical and subtropical Atlantic, including the variability of the NASH’s southern edge.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Previous studies have attributed interhemisphere influences of the atmosphere to the latitudinal propagation of planetary waves crossing the equator, to the triggering of equatorial Kelvin waves, or to monsoonal circulation. Over the American-Atlantic sector, such cross-equatorial influences rarely occur during boreal summer due to unfavorable atmospheric conditions. We have observed that an alternative mechanism provides an interhemisphere influence. When episodes of extreme cold surges and upper tropospheric westerly winds occur concurrently over southern hemisphere Amazonia, cold surges from extratropical South America can penetrate deep into southern Amazonia. Although they do not appear to influence upper tropospheric circulation of the northern hemisphere, extremely strong southerly cross-equatorial advection (>2σ standard deviations, or 2) of cold and dense air in the lower troposphere can reach as least 10°N. Such cold advection increases the northward cross-equatorial pressure gradient in the lower to middle troposphere, thus shallow northerly return flow below 500 hPa. This return flow and the strong lower tropospheric southerly cross-equatorial flow form an anomalous shallow meridional circulation spanning from southern Amazonia to the subtropical North Atlantic, with increased geopotential height anomalies exceeding +1σ to at least 18°N. It projects onto the southern edge of the North Atlantic Subtropical High (NASH), increasing its pressure and leading to equatorward expansion of NASH’s southern boundary. These anomalies enhance the NASH, leading to its equatorward expansion. These extreme cold surges can potentially improving the predictability of weather patterns of the tropical and subtropical Atlantic, including the variability of the NASH’s southern edge.
Zhang, Kai; Fu, Rong; Shaikh, M.; Ghan, S.; Wang, M.; Leung, L. R.; Dickinson, Robert E; Marengo, J.
Influence of Superparameterization and a Higher-Order Turbulence Closure on Rainfall Bias Over Amazonia in Community Atmosphere Model Version 5 Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 122, 2017.
@article{714,
title = {Influence of Superparameterization and a Higher-Order Turbulence Closure on Rainfall Bias Over Amazonia in Community Atmosphere Model Version 5},
author = {Kai Zhang and Rong Fu and M. Shaikh and S. Ghan and M. Wang and L. R. Leung and Robert E Dickinson and J. Marengo},
year = {2017},
date = {2017-09-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {122},
abstract = {We evaluate the Community Atmosphere Model Version 5 (CAM5) with a higher-order turbulence closure scheme, named Cloud Layers Unified By Binomials (CLUBB), and a Multiscale Modeling Framework, referred to as the “superparameterization” (SP) with two different microphysics configurations to investigate their influences on rainfall simulations over southern Amazonia. The two different microphysics configurations in SP are the one-moment cloud microphysics without aerosol treatment (SP1) and two-moment cloud microphysics coupled with aerosol treatment (SP2). Results show that both SP2 and CLUBB effectively reduce the low biases of rainfall, mainly during the wet season, and reduce low biases of humidity in the lower troposphere with further reduced shallow clouds and increased surface solar flux. These changes increase moist static energy in the lower atmosphere and contribute to stronger convection and more rainfall. SP2 appears to realistically capture the observed increase of relative humidity prior to deep convection, and it significantly increases rainfall in the afternoon; CLUBB significantly delays the afternoon peak rainfall and produces more precipitation in the early morning, due to more gradual transition between shallow and deep convection. In CAM5 and CAM5 with CLUBB, occurrence of more deep convection appears to be a result of stronger heating rather than higher relative humidity.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We evaluate the Community Atmosphere Model Version 5 (CAM5) with a higher-order turbulence closure scheme, named Cloud Layers Unified By Binomials (CLUBB), and a Multiscale Modeling Framework, referred to as the “superparameterization” (SP) with two different microphysics configurations to investigate their influences on rainfall simulations over southern Amazonia. The two different microphysics configurations in SP are the one-moment cloud microphysics without aerosol treatment (SP1) and two-moment cloud microphysics coupled with aerosol treatment (SP2). Results show that both SP2 and CLUBB effectively reduce the low biases of rainfall, mainly during the wet season, and reduce low biases of humidity in the lower troposphere with further reduced shallow clouds and increased surface solar flux. These changes increase moist static energy in the lower atmosphere and contribute to stronger convection and more rainfall. SP2 appears to realistically capture the observed increase of relative humidity prior to deep convection, and it significantly increases rainfall in the afternoon; CLUBB significantly delays the afternoon peak rainfall and produces more precipitation in the early morning, due to more gradual transition between shallow and deep convection. In CAM5 and CAM5 with CLUBB, occurrence of more deep convection appears to be a result of stronger heating rather than higher relative humidity.
Koster, R. D.; Betts, A. K.; Dirmeyer, P. A.; Bierkens, M.; Bennett, K. E.; Déry, S. J.; Evans, J. P.; Fu, R.; Hernandez, F.; Leung, L. R.; Liang, X.; Masood, M.; Savenije, H.; Wang, G.; Yuan, X.
Hydroclimatic variability and predictability: a survey of recent research Journal Article
In: Hydrology and Earth System Sciences, vol. 21, pp. 3777-3798, 2017.
@article{1281,
title = {Hydroclimatic variability and predictability: a survey of recent research},
author = {R. D. Koster and A. K. Betts and P. A. Dirmeyer and M. Bierkens and K. E. Bennett and S. J. Déry and J. P. Evans and R. Fu and F. Hernandez and L. R. Leung and X. Liang and M. Masood and H. Savenije and G. Wang and X. Yuan},
year = {2017},
date = {2017-07-01},
journal = {Hydrology and Earth System Sciences},
volume = {21},
pages = {3777-3798},
abstract = {Recent research in large-scale hydroclimatic variability is surveyed, focusing on five topics: (i) variability in general, (ii) droughts, (iii) floods, (iv) land–atmosphere coupling, and (v) hydroclimatic prediction. Each surveyed topic is supplemented by illustrative examples of recent research, as presented at a 2016 symposium honoring the career of Professor Eric Wood. Taken together, the recent literature and the illustrative examples clearly show that current research into hydroclimatic variability is strong, vibrant, and multifaceted.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Recent research in large-scale hydroclimatic variability is surveyed, focusing on five topics: (i) variability in general, (ii) droughts, (iii) floods, (iv) land–atmosphere coupling, and (v) hydroclimatic prediction. Each surveyed topic is supplemented by illustrative examples of recent research, as presented at a 2016 symposium honoring the career of Professor Eric Wood. Taken together, the recent literature and the illustrative examples clearly show that current research into hydroclimatic variability is strong, vibrant, and multifaceted.
Marengo, J. A.; Fisch, G. F.; Alves, L. M.; Sousa, N. V.; Fu, R.; Zhuang, Y.
Meteorological context of the onset and end of the rainy season in Central Amazonia during the GoAmazon2014/5 Journal Article
In: Atmospheric Chemistry and Physics, vol. 2017, no. 12, pp. 7671-7681, 2017.
@article{acp-2017-22,
title = {Meteorological context of the onset and end of the rainy season in Central Amazonia during the GoAmazon2014/5},
author = {J. A. Marengo and G. F. Fisch and L. M. Alves and N. V. Sousa and R. Fu and Y. Zhuang},
doi = {10.5194/acp-2017-22},
year = {2017},
date = {2017-06-01},
journal = {Atmospheric Chemistry and Physics},
volume = {2017},
number = {12},
pages = {7671-7681},
abstract = { The onset and demise of the rainy season in Amazonia are assessed in this study using meteorological data from the GoAmazon experiment, with a focus on the 2014–2015 rainy season. In addition, global reanalyses are also used to identify changes in circulation leading to the establishment of the rainy season in the region. Our results show that the onset occurred in January 2015, 2–3 pentads later than normal, and the rainy season during the austral summer of 2015 contained several periods with consecutive dry days in both Manacapuru and Manaus, which are not common for the wet season, and resulted in below-normal precipitation. The onset of the rainy season has been strongly associated with changes in large-scale weather conditions in the region due to the effect of the Madden–Julian Oscillation (MJO). Regional thermodynamic indices and the height of the boundary layer did not present a significant difference between the onset and demise of the wet season of 2015. This suggests that local changes, such as those in the regional thermodynamic characteristics, may not have influenced its onset. Thus, variability of the large-scale circulation was responsible for regional convection and rainfall changes in Amazonia during the austral summer of 2014–2015.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The onset and demise of the rainy season in Amazonia are assessed in this study using meteorological data from the GoAmazon experiment, with a focus on the 2014–2015 rainy season. In addition, global reanalyses are also used to identify changes in circulation leading to the establishment of the rainy season in the region. Our results show that the onset occurred in January 2015, 2–3 pentads later than normal, and the rainy season during the austral summer of 2015 contained several periods with consecutive dry days in both Manacapuru and Manaus, which are not common for the wet season, and resulted in below-normal precipitation. The onset of the rainy season has been strongly associated with changes in large-scale weather conditions in the region due to the effect of the Madden–Julian Oscillation (MJO). Regional thermodynamic indices and the height of the boundary layer did not present a significant difference between the onset and demise of the wet season of 2015. This suggests that local changes, such as those in the regional thermodynamic characteristics, may not have influenced its onset. Thus, variability of the large-scale circulation was responsible for regional convection and rainfall changes in Amazonia during the austral summer of 2014–2015.
Zhuang, Yizhou; Fu, Rong; Marengo, José A.; Wang, Hongqing
Seasonal variation of shallow-to-deep convection transition and its link to the environmental conditions over the Central Amazon Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 122, no. 5, pp. 2649–2666, 2017, ISSN: 2169897X.
@article{Zhuang2017,
title = {Seasonal variation of shallow-to-deep convection transition and its link to the environmental conditions over the Central Amazon},
author = {Yizhou Zhuang and Rong Fu and José A. Marengo and Hongqing Wang},
url = {http://doi.wiley.com/10.1002/2013JD021060 http://doi.wiley.com/10.1002/2016JD025993},
doi = {10.1002/2016JD025993},
issn = {2169897X},
year = {2017},
date = {2017-03-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {122},
number = {5},
pages = {2649–2666},
abstract = {We analyze simulated sea ice changes in eight different Earth System Models that have conducted experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP). The simulated response of balancing abrupt quadrupling of CO 2 (abrupt4xCO2) with reduced shortwave radiation successfully moderates annually averaged Arctic temperature rise to about 1°C, with modest changes in seasonal sea ice cycle compared with the preindustrial control simulations (piControl). Changes in summer and autumn sea ice extent are spatially correlated with temperature patterns but much less in winter and spring seasons. However, there are changes of ±20% in sea ice concentration in all seasons, and these will induce changes in atmospheric circulation patterns. In summer and autumn, the models consistently simulate less sea ice relative to preindustrial simulations in the Beaufort, Chukchi, East Siberian, and Laptev Seas, and some models show increased sea ice in the Barents/Kara Seas region. Sea ice extent increases in the Greenland Sea, particularly in winter and spring and is to some extent associated with changed sea ice drift. Decreased sea ice cover in winter and spring in the Barents Sea is associated with increased cyclonic activity entering this area under G1. In comparison, the abrupt4xCO2 experiment shows almost total sea ice loss in September and strong correlation with regional temperatures in all seasons consistent with open ocean conditions. The tropospheric circulation displays a Paci fi c North America pattern-like anomaly with negative phase in G1-piControl and positive phase under abrupt4xCO2-piControl.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We analyze simulated sea ice changes in eight different Earth System Models that have conducted experiment G1 of the Geoengineering Model Intercomparison Project (GeoMIP). The simulated response of balancing abrupt quadrupling of CO 2 (abrupt4xCO2) with reduced shortwave radiation successfully moderates annually averaged Arctic temperature rise to about 1°C, with modest changes in seasonal sea ice cycle compared with the preindustrial control simulations (piControl). Changes in summer and autumn sea ice extent are spatially correlated with temperature patterns but much less in winter and spring seasons. However, there are changes of ±20% in sea ice concentration in all seasons, and these will induce changes in atmospheric circulation patterns. In summer and autumn, the models consistently simulate less sea ice relative to preindustrial simulations in the Beaufort, Chukchi, East Siberian, and Laptev Seas, and some models show increased sea ice in the Barents/Kara Seas region. Sea ice extent increases in the Greenland Sea, particularly in winter and spring and is to some extent associated with changed sea ice drift. Decreased sea ice cover in winter and spring in the Barents Sea is associated with increased cyclonic activity entering this area under G1. In comparison, the abrupt4xCO2 experiment shows almost total sea ice loss in September and strong correlation with regional temperatures in all seasons consistent with open ocean conditions. The tropospheric circulation displays a Paci fi c North America pattern-like anomaly with negative phase in G1-piControl and positive phase under abrupt4xCO2-piControl.
Wright, Jonathon S.; Fu, Rong; Worden, John R.; Chakraborty, Sudip; Clinton, Nicholas E.; Risi, Camille; Sun, Ying; Yin, Lei
A rainforest initiated wet season onset over the southern Amazon Journal Article
In: Proceedings of the National Academy of Sciences, vol. 114, no. 32, pp. 8481-8486, 2017.
@article{715,
title = {A rainforest initiated wet season onset over the southern Amazon},
author = {Jonathon S. Wright and Rong Fu and John R. Worden and Sudip Chakraborty and Nicholas E. Clinton and Camille Risi and Ying Sun and Lei Yin},
url = {https://www.pnas.org/content/114/32/8481},
year = {2017},
date = {2017-01-01},
journal = {Proceedings of the National Academy of Sciences},
volume = {114},
number = {32},
pages = {8481-8486},
abstract = {Although it is well established that transpiration contributes much of the water for rainfall over Amazonia, it remains unclear whether transpiration helps to drive or merely responds to the seasonal cycle of rainfall. Here, we use multiple independent satellite datasets to show that rainforest transpiration enables an increase of shallow convection that moistens and destabilizes the atmosphere during the initial stages of the dry-to-wet season transition. This shallow convection moisture pump (SCMP) preconditions the atmosphere at the regional scale for a rapid increase in rain-bearing deep convection, which in turn drives moisture convergence and wet season onset 2–3 mo before the arrival of the Intertropical Convergence Zone (ITCZ). Aerosols produced by late dry season biomass burning may alter the efficiency of the SCMP. Our results highlight the mechanisms by which interactions among land surface processes, atmospheric convection, and biomass burning may alter the timing of wet season onset and provide a mechanistic framework for understanding how deforestation extends the dry season and enhances regional vulnerability to drought.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Although it is well established that transpiration contributes much of the water for rainfall over Amazonia, it remains unclear whether transpiration helps to drive or merely responds to the seasonal cycle of rainfall. Here, we use multiple independent satellite datasets to show that rainforest transpiration enables an increase of shallow convection that moistens and destabilizes the atmosphere during the initial stages of the dry-to-wet season transition. This shallow convection moisture pump (SCMP) preconditions the atmosphere at the regional scale for a rapid increase in rain-bearing deep convection, which in turn drives moisture convergence and wet season onset 2–3 mo before the arrival of the Intertropical Convergence Zone (ITCZ). Aerosols produced by late dry season biomass burning may alter the efficiency of the SCMP. Our results highlight the mechanisms by which interactions among land surface processes, atmospheric convection, and biomass burning may alter the timing of wet season onset and provide a mechanistic framework for understanding how deforestation extends the dry season and enhances regional vulnerability to drought.
Alves, Lincoln Muniz; Marengo, Jose A.; Fu, Rong; Bombardi, Rodrigo J.
Sensitivity of Amazon Regional Climate to Deforestation Journal Article
In: American Journal of Climate Change, vol. 06, no. 01, pp. 75–98, 2017, ISSN: 2167-9495.
@article{Alves2017,
title = {Sensitivity of Amazon Regional Climate to Deforestation},
author = {Lincoln Muniz Alves and Jose A. Marengo and Rong Fu and Rodrigo J. Bombardi},
url = {http://www.scirp.org/journal/PaperDownload.aspx?DOI=10.4236/ajcc.2017.61005},
doi = {10.4236/ajcc.2017.61005},
issn = {2167-9495},
year = {2017},
date = {2017-01-01},
journal = {American Journal of Climate Change},
volume = {06},
number = {01},
pages = {75–98},
abstract = {It is known that the Amazon region plays an important role in the global energy, hydrological cycle and carbon balance. This region has been suffering from the course of the past 40 years intense land use and land cover changes. With this in mind, this study has examined possible associations between change in spatial and temporal rainfall variability and land cover change in the Amazon, using the PRECIS regional modelling system. It has been found that the impacts of land cover change by forest removal are more intense in the so-called “Arc of deforestation” over central and southern Amazonia. However, the relative impact of the simulated rainfall changes seems to be more important in the JJA dry season. In addition, the simulations under the deforestation scenarios also show the occurrence of extreme rainfall events as well as more frequent dry periods. Therefore, the results found show to be potentially important in the modulation of regional climate variations which have several environmental and socio-economic impacts.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
It is known that the Amazon region plays an important role in the global energy, hydrological cycle and carbon balance. This region has been suffering from the course of the past 40 years intense land use and land cover changes. With this in mind, this study has examined possible associations between change in spatial and temporal rainfall variability and land cover change in the Amazon, using the PRECIS regional modelling system. It has been found that the impacts of land cover change by forest removal are more intense in the so-called “Arc of deforestation” over central and southern Amazonia. However, the relative impact of the simulated rainfall changes seems to be more important in the JJA dry season. In addition, the simulations under the deforestation scenarios also show the occurrence of extreme rainfall events as well as more frequent dry periods. Therefore, the results found show to be potentially important in the modulation of regional climate variations which have several environmental and socio-economic impacts.
2016
Fernando, D. Nelun; Mo, Kingtse C.; Fu, Rong; Pu, Bing; Bowerman, Adam; Scanlon, Bridget R.; Solis, Ruben S.; Yin, Lei; Mace, Robert E.; Mioduszewski, John R.; Ren, Tong; Zhang, Kai
What caused the spring intensification and winter demise of the 2011 drought over Texas? Journal Article
In: Climate Dynamics, vol. 47, no. 9-10, pp. 3077–3090, 2016, ISSN: 0930-7575.
@article{Fernando2016,
title = {What caused the spring intensification and winter demise of the 2011 drought over Texas?},
author = {D. Nelun Fernando and Kingtse C. Mo and Rong Fu and Bing Pu and Adam Bowerman and Bridget R. Scanlon and Ruben S. Solis and Lei Yin and Robert E. Mace and John R. Mioduszewski and Tong Ren and Kai Zhang},
url = {http://link.springer.com/10.1007/s00382-016-3014-x},
doi = {10.1007/s00382-016-3014-x},
issn = {0930-7575},
year = {2016},
date = {2016-11-01},
journal = {Climate Dynamics},
volume = {47},
number = {9-10},
pages = {3077–3090},
publisher = {Springer Berlin Heidelberg},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Chakraborty, Sudip; Fu, Rong; Massie, Steven T; Stephens, Graeme
Relative influence of meteorological conditions and aerosols on the lifetime of mesoscale convective systems Journal Article
In: Proceedings of the National Academy of Sciences, vol. 113, no. 27, pp. 7426–7431, 2016, ISSN: 0027-8424.
@article{Chakraborty2016,
title = {Relative influence of meteorological conditions and aerosols on the lifetime of mesoscale convective systems},
author = {Sudip Chakraborty and Rong Fu and Steven T Massie and Graeme Stephens},
url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1601935113},
doi = {10.1073/pnas.1601935113},
issn = {0027-8424},
year = {2016},
date = {2016-07-01},
journal = {Proceedings of the National Academy of Sciences},
volume = {113},
number = {27},
pages = {7426–7431},
abstract = {Using collocated measurements from geostationary and polar-orbital satellites over tropical continents, we provide a large-scale statistical assessment of the relative influence of aerosols and meteorological conditions on the lifetime of mesoscale convective systems (MCSs). Our results show that MCSs’ lifetime increases by 3–24 h when ver-tical wind shear (VWS) and convective available potential energy (CAPE) are moderate to high and ambient aerosol optical depth (AOD) increases by 1 SD (1σ). However, this influence is not as strong as that of CAPE, relative humidity, and VWS, which increase MCSs’ lifetime by 3–30 h, 3–27 h, and 3–30 h per 1σ of these variables and explain up to 36%, 45%, and 34%, respectively, of the variance of the MCSs’ lifetime. AOD explains up to 24% of the total variance of MCSs’ lifetime during the decay phase. This result is physically con-sistent with that of the variation of the MCSs’ ice water content (IWC) with aerosols, which accounts for 35% and 27% of the total variance of the IWC in convective cores and anvil, respectively, dur-ing the decay phase. The effect of aerosols on MCSs’ lifetime varies between different continents. AOD appears to explain up to 20–22% of the total variance of MCSs’ lifetime over equatorial South America compared with 8% over equatorial Africa. Aerosols over the Indian Ocean can explain 20% of total variance of MCSs’ lifetime over South Asia because such MCSs form and develop over the ocean. These regional differences of aerosol impacts may be linked to different meteorological conditions. mesoscale convective systems | aerosols | meteorological parameters T he hypothesis that aerosols may delay precipitation and increase cloud lifetime of shallow marine clouds (1) has motivated many researchers to study the aerosol indirect effect on convective clouds; however, the influence of aerosols on enhancing cloud lifetime has remained under debate. Mesoscale convective systems (MCSs) are deep convective clouds that cover several hundred kilometers. Previous studies have shown that aerosols affect deep convection, in particular that aerosols increase the number of smaller size cloud condensation nuclei (CCN) (2), which weaken coagulation and coalescence that form rain droplets, and consequently delay warm rainfall (3, 4). These processes allow more cloud droplets to rise above the freezing level and increase latent heat released due to glaciation (5), resulting in stronger updraft speed, enhanced cloud ice content (6), larger anvil size (5), and higher cloud top height (7). The top of the troposphere warms owing to the aerosol-induced changes in convective anvils (8). Although these aerosol effects have been seen in observations from field cam-paigns (9, 10), they have been undetectable on large spatial and multiyear scales. Rosenfeld et al. (11) have attributed this lack of detectability on the large scale of aerosol invigoration of convec-tion to its variation with meteorological conditions and to the lack of knowledge of the relative humidity (RH) outside the clouds. The variation of aerosol effects on convection with meteoro-logical parameters has been studied previously (11). For example, model simulation has shown that an increase in aerosol concen-trations up to an optimal level can invigorate the MCSs under weak vertical wind shear (VWS) and higher RH but suppress the MCSs under strong VWS in a dry environment (12, 13). They found that, due to a significant enhancement in the convective available po-tential energy (CAPE), corresponding to an increase in RH from 50% to 70%, aerosol impact on ice crystal mass becomes pro-nounced, with a dramatic increase in the size of the anvils and the mass of ice crystals of the deep convection. However, such impacts are negligible when RH increases from 40% to 50%, due to little increase in CAPE (13). Moreover, consumption of CAPE for a given amount of rainfall is converted to an equal amount of kinetic energy that invigorates the convection (5, 14). These studies indicate that VWS, RH, and CAPE are important factors that can influence aerosol impacts on the MCSs. However, no quantitative assessment of the relative influence of aerosols versus these meteorological parameters on convective lifetime using satellite measurements has been established (11). The influence of aerosols on the MCSs is expected to vary in different phases of the convective life cycle. For example, Rosenfeld et al. (5) hypothesized that the impact of aerosol on deep convec-tion is stronger and more prominent during the dissipating phase. Using cloud-resolving simulations, Fan et al. (15) found out that aerosol microphysical effects intensify the deep convection during the mature and decaying phases by forming a larger number of smaller and long-lasting particles, whereas additional latent heat released due to aerosols’ thermodynamic effect is responsible for invigorating the deep convections during the growing phase. Hence, the detection of aerosol impacts might not be visible until the mature phase, as no satellite can directly measure the thermo-dynamic properties.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Using collocated measurements from geostationary and polar-orbital satellites over tropical continents, we provide a large-scale statistical assessment of the relative influence of aerosols and meteorological conditions on the lifetime of mesoscale convective systems (MCSs). Our results show that MCSs’ lifetime increases by 3–24 h when ver-tical wind shear (VWS) and convective available potential energy (CAPE) are moderate to high and ambient aerosol optical depth (AOD) increases by 1 SD (1σ). However, this influence is not as strong as that of CAPE, relative humidity, and VWS, which increase MCSs’ lifetime by 3–30 h, 3–27 h, and 3–30 h per 1σ of these variables and explain up to 36%, 45%, and 34%, respectively, of the variance of the MCSs’ lifetime. AOD explains up to 24% of the total variance of MCSs’ lifetime during the decay phase. This result is physically con-sistent with that of the variation of the MCSs’ ice water content (IWC) with aerosols, which accounts for 35% and 27% of the total variance of the IWC in convective cores and anvil, respectively, dur-ing the decay phase. The effect of aerosols on MCSs’ lifetime varies between different continents. AOD appears to explain up to 20–22% of the total variance of MCSs’ lifetime over equatorial South America compared with 8% over equatorial Africa. Aerosols over the Indian Ocean can explain 20% of total variance of MCSs’ lifetime over South Asia because such MCSs form and develop over the ocean. These regional differences of aerosol impacts may be linked to different meteorological conditions. mesoscale convective systems | aerosols | meteorological parameters T he hypothesis that aerosols may delay precipitation and increase cloud lifetime of shallow marine clouds (1) has motivated many researchers to study the aerosol indirect effect on convective clouds; however, the influence of aerosols on enhancing cloud lifetime has remained under debate. Mesoscale convective systems (MCSs) are deep convective clouds that cover several hundred kilometers. Previous studies have shown that aerosols affect deep convection, in particular that aerosols increase the number of smaller size cloud condensation nuclei (CCN) (2), which weaken coagulation and coalescence that form rain droplets, and consequently delay warm rainfall (3, 4). These processes allow more cloud droplets to rise above the freezing level and increase latent heat released due to glaciation (5), resulting in stronger updraft speed, enhanced cloud ice content (6), larger anvil size (5), and higher cloud top height (7). The top of the troposphere warms owing to the aerosol-induced changes in convective anvils (8). Although these aerosol effects have been seen in observations from field cam-paigns (9, 10), they have been undetectable on large spatial and multiyear scales. Rosenfeld et al. (11) have attributed this lack of detectability on the large scale of aerosol invigoration of convec-tion to its variation with meteorological conditions and to the lack of knowledge of the relative humidity (RH) outside the clouds. The variation of aerosol effects on convection with meteoro-logical parameters has been studied previously (11). For example, model simulation has shown that an increase in aerosol concen-trations up to an optimal level can invigorate the MCSs under weak vertical wind shear (VWS) and higher RH but suppress the MCSs under strong VWS in a dry environment (12, 13). They found that, due to a significant enhancement in the convective available po-tential energy (CAPE), corresponding to an increase in RH from 50% to 70%, aerosol impact on ice crystal mass becomes pro-nounced, with a dramatic increase in the size of the anvils and the mass of ice crystals of the deep convection. However, such impacts are negligible when RH increases from 40% to 50%, due to little increase in CAPE (13). Moreover, consumption of CAPE for a given amount of rainfall is converted to an equal amount of kinetic energy that invigorates the convection (5, 14). These studies indicate that VWS, RH, and CAPE are important factors that can influence aerosol impacts on the MCSs. However, no quantitative assessment of the relative influence of aerosols versus these meteorological parameters on convective lifetime using satellite measurements has been established (11). The influence of aerosols on the MCSs is expected to vary in different phases of the convective life cycle. For example, Rosenfeld et al. (5) hypothesized that the impact of aerosol on deep convec-tion is stronger and more prominent during the dissipating phase. Using cloud-resolving simulations, Fan et al. (15) found out that aerosol microphysical effects intensify the deep convection during the mature and decaying phases by forming a larger number of smaller and long-lasting particles, whereas additional latent heat released due to aerosols’ thermodynamic effect is responsible for invigorating the deep convections during the growing phase. Hence, the detection of aerosol impacts might not be visible until the mature phase, as no satellite can directly measure the thermo-dynamic properties.
Gao, HL; Zhang, S; Fu, R; Li, WH; Dickinson, RE
Interannual Variation of the Surface Temperature of Tropical Forests from Satellite Observations Journal Article
In: Advances in Meteorology, vol. 2016, pp. 1-11, 2016.
@article{1248,
title = {Interannual Variation of the Surface Temperature of Tropical Forests from Satellite Observations},
author = {HL Gao and S Zhang and R Fu and WH Li and RE Dickinson},
url = {https://www.hindawi.com/journals/amete/2016/4741390/},
year = {2016},
date = {2016-05-01},
journal = {Advances in Meteorology},
volume = {2016},
pages = {1-11},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Pu, Bing; Dickinson, Robert E.; Fu, Rong
Dynamical connection between Great Plains low-level winds and variability of central Gulf States precipitation Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 121, no. 7, pp. 3421–3434, 2016, ISSN: 2169897X.
@article{Pu2016a,
title = {Dynamical connection between Great Plains low-level winds and variability of central Gulf States precipitation},
author = {Bing Pu and Robert E. Dickinson and Rong Fu},
url = {http://doi.wiley.com/10.1002/2015JD024045},
doi = {10.1002/2015JD024045},
issn = {2169897X},
year = {2016},
date = {2016-04-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {121},
number = {7},
pages = {3421–3434},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Pu, Bing; Fu, Rong; Dickinson, Robert E.; Fernando, D. Nelun
Why do summer droughts in the Southern Great Plains occur in some La Niña years but not others? Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 121, no. 3, pp. 1120–1137, 2016, ISSN: 2169897X.
@article{Pu2016,
title = {Why do summer droughts in the Southern Great Plains occur in some La Niña years but not others?},
author = {Bing Pu and Rong Fu and Robert E. Dickinson and D. Nelun Fernando},
url = {http://doi.wiley.com/10.1002/2015JD023508},
doi = {10.1002/2015JD023508},
issn = {2169897X},
year = {2016},
date = {2016-02-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {121},
number = {3},
pages = {1120–1137},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Zhang, K.; Fu, R.; Wang, T.; Liu, Y.
Impact of geographic variations of convective and dehydration center on stratospheric water vapor over the Asian monsoon region Journal Article
In: Atmospheric Chemistry and Physics Discussions, pp. 1–19, 2016, ISSN: 1680-7375.
@article{Zhang2016,
title = {Impact of geographic variations of convective and dehydration center on stratospheric water vapor over the Asian monsoon region},
author = {K. Zhang and R. Fu and T. Wang and Y. Liu},
url = {http://www.atmos-chem-phys-discuss.net/acp-2016-21/},
doi = {10.5194/acp-2016-21},
issn = {1680-7375},
year = {2016},
date = {2016-01-01},
journal = {Atmospheric Chemistry and Physics Discussions},
pages = {1–19},
abstract = {The Asian monsoon region is the most prominent moisture center of lower stratospheric (LS) water vapor during boreal summer. Previous studies have suggested that the transport of water vapor to the Asian monsoon LS is controlled by dehydration temperatures and convection mainly over the Bay of Bengal and Southeast Asia. However, there is a clear geographic variation of convection associated with the seasonal and intra-seasonal variations of the Asian monsoon circulation, and the relative influence of such a geographic variation of convection vs. the variation of local dehydration temperatures on water vapor transport is still not clear. Using the Aura Microwave Limb Sounder (MLS) satellite observations and a domain-filling forward trajectory model, we show that almost half of the seasonal water vapor increase in the Asian monsoon LS are attributable to the geographic variations of convection and resultant variations of dehydration center, comparable to the influence of the local dehydration temperature increase. In particular, dehydration temperatures are coldest over the southeast and warmest over the northwest within the Asian monsoon region. Although convective center is located over the southeastern Asia, an anomalous increase of convection over the northwestern Asian monsoon region increases the local diabatic heating in the tropopause layer and air mass entering the LS that is dehydrated at relatively warm er temperatures. The warmer dehydration temperatures allow anomalously moist air enters the LS and then moves eastward along the northern frank of the monsoon anticyclonic flow, leading to wet anomalies in the LS over the Asian monsoon region. Likewise, when convection increases over the southeastern Asian monsoon region, dry anomalies appear in the LS. On seasonal scale, this feature is associated with the march of the monsoon circulation, convection and diabatic heating towards the northwestern Asia monsoon from June to August, leading to an increasing fraction of the air mass to be dehydrated at warmer temperatures over the nort hwestern Asian monsoon region. Work presented here confirms the dominant role of temper atures and also emphasizes that one should take the geographic variations of dehydration center into consideration when studying water vapor variations in the LS, as it is linked to changes of convection and large-scale circulation.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The Asian monsoon region is the most prominent moisture center of lower stratospheric (LS) water vapor during boreal summer. Previous studies have suggested that the transport of water vapor to the Asian monsoon LS is controlled by dehydration temperatures and convection mainly over the Bay of Bengal and Southeast Asia. However, there is a clear geographic variation of convection associated with the seasonal and intra-seasonal variations of the Asian monsoon circulation, and the relative influence of such a geographic variation of convection vs. the variation of local dehydration temperatures on water vapor transport is still not clear. Using the Aura Microwave Limb Sounder (MLS) satellite observations and a domain-filling forward trajectory model, we show that almost half of the seasonal water vapor increase in the Asian monsoon LS are attributable to the geographic variations of convection and resultant variations of dehydration center, comparable to the influence of the local dehydration temperature increase. In particular, dehydration temperatures are coldest over the southeast and warmest over the northwest within the Asian monsoon region. Although convective center is located over the southeastern Asia, an anomalous increase of convection over the northwestern Asian monsoon region increases the local diabatic heating in the tropopause layer and air mass entering the LS that is dehydrated at relatively warm er temperatures. The warmer dehydration temperatures allow anomalously moist air enters the LS and then moves eastward along the northern frank of the monsoon anticyclonic flow, leading to wet anomalies in the LS over the Asian monsoon region. Likewise, when convection increases over the southeastern Asian monsoon region, dry anomalies appear in the LS. On seasonal scale, this feature is associated with the march of the monsoon circulation, convection and diabatic heating towards the northwestern Asia monsoon from June to August, leading to an increasing fraction of the air mass to be dehydrated at warmer temperatures over the nort hwestern Asian monsoon region. Work presented here confirms the dominant role of temper atures and also emphasizes that one should take the geographic variations of dehydration center into consideration when studying water vapor variations in the LS, as it is linked to changes of convection and large-scale circulation.
2015
a. Arias, Paola; Fu, Rong; Vera, Carolina; Rojas, Maisa
A correlated shortening of the North and South American monsoon seasons in the past few decades Journal Article
In: Climate Dynamics, vol. 45, no. 11-12, pp. 3183–3203, 2015, ISSN: 0930-7575.
@article{Arias2015,
title = {A correlated shortening of the North and South American monsoon seasons in the past few decades},
author = {Paola a. Arias and Rong Fu and Carolina Vera and Maisa Rojas},
url = {http://link.springer.com/10.1007/s00382-015-2533-1},
doi = {10.1007/s00382-015-2533-1},
issn = {0930-7575},
year = {2015},
date = {2015-12-01},
journal = {Climate Dynamics},
volume = {45},
number = {11-12},
pages = {3183–3203},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Sun, Ying; Fu, Rong; Dickinson, Robert; Joiner, Joanna; Frankenberg, Christian; Gu, Lianhong; Xia, Youlong; Fernando, Nelun
Drought onset mechanisms revealed by satellite solar-induced chlorophyll fluorescence: Insights from two contrasting extreme events Journal Article
In: Journal of Geophysical Research: Biogeosciences, vol. 120, no. 11, pp. 2427–2440, 2015, ISSN: 21698953.
@article{Sun2015,
title = {Drought onset mechanisms revealed by satellite solar-induced chlorophyll fluorescence: Insights from two contrasting extreme events},
author = {Ying Sun and Rong Fu and Robert Dickinson and Joanna Joiner and Christian Frankenberg and Lianhong Gu and Youlong Xia and Nelun Fernando},
url = {http://doi.wiley.com/10.1002/2015JG003150},
doi = {10.1002/2015JG003150},
issn = {21698953},
year = {2015},
date = {2015-11-01},
journal = {Journal of Geophysical Research: Biogeosciences},
volume = {120},
number = {11},
pages = {2427–2440},
abstract = {This study uses the droughts of 2011 in Texas and 2012 over the central Great Plains as case studies to explore the potential of satellite-observed solar-induced chlorophyll fluorescence (SIF) for monitoring drought dynamics.We find that the spatial patterns of negative SIF anomalies from the Global Ozone Monitoring Experiment 2 (GOME-2) closely resembled drought intensity maps from the U.S. DroughtMonitor for both events. The drought-induced suppression of SIF occurred throughout 2011 but was exacerbated in summer in the Texas drought. This event was characterized by a persistent depletion of root zone soil moisture caused by yearlong below-normal precipitation. In contrast, for the central Great Plains drought, warmer temperatures and relatively normal precipitation boosted SIF in the spring of 2012; however, a sudden drop in precipitation coupled with unusually high temperatures rapidly depleted soil moisture through evapotranspiration, leading to a rapid onset of drought in early summer. Accordingly, SIF reversed from above to below normal. For both regions, the GOME-2 SIF anomalies were significantly correlated with those of root zone soil moisture, indicating that the former can potentially be used as proxy of the latter for monitoring agricultural droughts with different onset mechanisms. Further analyses indicate that the contrasting dynamics of SIF during these two extreme events were caused by changes in both fraction of absorbed photosynthetically active radiation fPAR and fluorescence yield, suggesting that satellite SIF is sensitive to both structural and physiological/biochemical variations of vegetation. We conclude that the emerging satellite SIF has excellent potential for dynamic drought monitoring.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
This study uses the droughts of 2011 in Texas and 2012 over the central Great Plains as case studies to explore the potential of satellite-observed solar-induced chlorophyll fluorescence (SIF) for monitoring drought dynamics.We find that the spatial patterns of negative SIF anomalies from the Global Ozone Monitoring Experiment 2 (GOME-2) closely resembled drought intensity maps from the U.S. DroughtMonitor for both events. The drought-induced suppression of SIF occurred throughout 2011 but was exacerbated in summer in the Texas drought. This event was characterized by a persistent depletion of root zone soil moisture caused by yearlong below-normal precipitation. In contrast, for the central Great Plains drought, warmer temperatures and relatively normal precipitation boosted SIF in the spring of 2012; however, a sudden drop in precipitation coupled with unusually high temperatures rapidly depleted soil moisture through evapotranspiration, leading to a rapid onset of drought in early summer. Accordingly, SIF reversed from above to below normal. For both regions, the GOME-2 SIF anomalies were significantly correlated with those of root zone soil moisture, indicating that the former can potentially be used as proxy of the latter for monitoring agricultural droughts with different onset mechanisms. Further analyses indicate that the contrasting dynamics of SIF during these two extreme events were caused by changes in both fraction of absorbed photosynthetically active radiation fPAR and fluorescence yield, suggesting that satellite SIF is sensitive to both structural and physiological/biochemical variations of vegetation. We conclude that the emerging satellite SIF has excellent potential for dynamic drought monitoring.
Lin, Changgui; Yang, Kun; Huang, Jianping; Tang, Wenjun; Qin, Jun; Niu, Xiaolei; Chen, Yingying; Chen, Deliang; Lu, Ning; Fu, Rong
Impacts of wind stilling on solar radiation variability in China Journal Article
In: Scientific Reports, vol. 5, pp. 15135, 2015, ISSN: 2045-2322.
@article{Lin2015,
title = {Impacts of wind stilling on solar radiation variability in China},
author = {Changgui Lin and Kun Yang and Jianping Huang and Wenjun Tang and Jun Qin and Xiaolei Niu and Yingying Chen and Deliang Chen and Ning Lu and Rong Fu},
url = {http://dx.doi.org/10.1038/srep15135%5Cnhttp://www.nature.com/srep/2015/151014/srep15135/full/srep15135.html http://www.nature.com/articles/srep15135},
doi = {10.1038/srep15135},
issn = {2045-2322},
year = {2015},
date = {2015-10-01},
journal = {Scientific Reports},
volume = {5},
pages = {15135},
publisher = {Nature Publishing Group},
abstract = {Solar dimming and wind stilling (slowdown) are two outstanding climate changes occurred in China over the last four decades. The wind stilling may have suppressed the dispersion of aerosols and amplified the impact of aerosol emission on solar dimming. However, there is a lack of long-term aerosol monitoring and associated study in China to confirm this hypothesis. Here, long-term meteorological data at weather stations combined with short-term aerosol data were used to assess this hypothesis. It was found that surface solar radiation (SSR) decreased considerably with wind stilling in heavily polluted regions at a daily scale, indicating that wind stilling can considerably amplify the aerosol extinction effect on SSR. A threshold value of 3.5 m/s for wind speed is required to effectively reduce aerosols concentration. From this SSR dependence on wind speed, we further derived proxies to quantify aerosol emission and wind stilling amplification effects on SSR variations at a decadal scale. The results show that aerosol emission accounted for approximately 20% of the typical solar dimming in China, which was amplified by approximately 20% by wind stilling.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Solar dimming and wind stilling (slowdown) are two outstanding climate changes occurred in China over the last four decades. The wind stilling may have suppressed the dispersion of aerosols and amplified the impact of aerosol emission on solar dimming. However, there is a lack of long-term aerosol monitoring and associated study in China to confirm this hypothesis. Here, long-term meteorological data at weather stations combined with short-term aerosol data were used to assess this hypothesis. It was found that surface solar radiation (SSR) decreased considerably with wind stilling in heavily polluted regions at a daily scale, indicating that wind stilling can considerably amplify the aerosol extinction effect on SSR. A threshold value of 3.5 m/s for wind speed is required to effectively reduce aerosols concentration. From this SSR dependence on wind speed, we further derived proxies to quantify aerosol emission and wind stilling amplification effects on SSR variations at a decadal scale. The results show that aerosol emission accounted for approximately 20% of the typical solar dimming in China, which was amplified by approximately 20% by wind stilling.
Randel, William J; Zhang, Kai; Fu, Rong
What controls stratospheric water vapor in the NH summer monsoon regions? Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 120, no. 15, pp. 7988–8001, 2015, ISSN: 2169897X.
@article{Randel2015,
title = {What controls stratospheric water vapor in the NH summer monsoon regions?},
author = {William J Randel and Kai Zhang and Rong Fu},
url = {http://doi.wiley.com/10.1002/2015JD023622},
doi = {10.1002/2015JD023622},
issn = {2169897X},
year = {2015},
date = {2015-08-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {120},
number = {15},
pages = {7988–8001},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Chakraborty, Sudip; Fu, Rong; Wright, Jonathon S.; Massie, Steven T.
Relationships between convective structure and transport of aerosols to the upper troposphere deduced from satellite observations Journal Article
In: Journal of Geophysical Research: Atmospheres, vol. 120, no. 13, pp. 6515–6536, 2015, ISSN: 2169897X.
@article{Chakraborty2015,
title = {Relationships between convective structure and transport of aerosols to the upper troposphere deduced from satellite observations},
author = {Sudip Chakraborty and Rong Fu and Jonathon S. Wright and Steven T. Massie},
url = {http://doi.wiley.com/10.1002/2015JD023528},
doi = {10.1002/2015JD023528},
issn = {2169897X},
year = {2015},
date = {2015-07-01},
journal = {Journal of Geophysical Research: Atmospheres},
volume = {120},
number = {13},
pages = {6515–6536},
abstract = {We estimate the extent of upper tropospheric aerosol layers (UT ALs) surrounding mesoscale convective systems (MCSs) and explore the relationships between UT AL extent and the morphology, location, and developmental stage of collocated MCSs in the tropics. Our analysis is based on satellite data collected over equatorial Africa, South Asia, and the Amazon basin between June 2006 and June 2008. We identify substantial variations in the relationships between convective properties and aerosol transport by region and stage of convective development. The most extensive UT ALs over equatorial Africa are associated with mature MCSs, while the most extensive UT ALs over South Asia and the Amazon are associated with growing MCSs. Convective aerosol transport over the Amazon is weaker than that observed over the other two regions despite similar transport frequencies, likely due to the smaller sizes and shorter mean lifetimes of MCSs over the Amazon. Variations in UT ALs in the vicinity of tropical MCSs are primarily explained by variations in the horizontal sizes of the associated MCSs and are largely unrelated to aerosol loading in the lower troposphere. We also identify potentially important relationships with the number of convective cores, vertical wind shear, and convective fraction during the growing and mature stages of MCS development. Relationships between convective properties and aerosol transport are relatively weak during the decaying stage of convective development. Our results provide an interpretive framework for devising and evaluating numerical model experiments that examine relationships between convective properties and ALs in the upper troposphere.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We estimate the extent of upper tropospheric aerosol layers (UT ALs) surrounding mesoscale convective systems (MCSs) and explore the relationships between UT AL extent and the morphology, location, and developmental stage of collocated MCSs in the tropics. Our analysis is based on satellite data collected over equatorial Africa, South Asia, and the Amazon basin between June 2006 and June 2008. We identify substantial variations in the relationships between convective properties and aerosol transport by region and stage of convective development. The most extensive UT ALs over equatorial Africa are associated with mature MCSs, while the most extensive UT ALs over South Asia and the Amazon are associated with growing MCSs. Convective aerosol transport over the Amazon is weaker than that observed over the other two regions despite similar transport frequencies, likely due to the smaller sizes and shorter mean lifetimes of MCSs over the Amazon. Variations in UT ALs in the vicinity of tropical MCSs are primarily explained by variations in the horizontal sizes of the associated MCSs and are largely unrelated to aerosol loading in the lower troposphere. We also identify potentially important relationships with the number of convective cores, vertical wind shear, and convective fraction during the growing and mature stages of MCS development. Relationships between convective properties and aerosol transport are relatively weak during the decaying stage of convective development. Our results provide an interpretive framework for devising and evaluating numerical model experiments that examine relationships between convective properties and ALs in the upper troposphere.
Bi, Jian; Knyazikhin, Yuri; Choi, Sungho; Park, Taejin; Barichivich, Jonathan; Ciais, Philippe; Fu, Rong; Ganguly, Sangram; Hall, Forrest; Hilker, Thomas; Huete, Alfredo; Jones, Matthew; Kimball, John; Lyapustin, Alexei I; Mõttus, Matti; Nemani, Ramakrishna R; Piao, Shilong; Poulter, Benjamin; Saleska, Scott R; Saatchi, Sassan S; Xu, Liang; Zhou, Liming; Myneni, Ranga B
Sunlight mediated seasonality in canopy structure and photosynthetic activity of Amazonian rainforests Journal Article
In: Environmental Research Letters, vol. 10, no. 6, pp. 064014, 2015, ISSN: 1748-9326.
@article{Bi2015,
title = {Sunlight mediated seasonality in canopy structure and photosynthetic activity of Amazonian rainforests},
author = {Jian Bi and Yuri Knyazikhin and Sungho Choi and Taejin Park and Jonathan Barichivich and Philippe Ciais and Rong Fu and Sangram Ganguly and Forrest Hall and Thomas Hilker and Alfredo Huete and Matthew Jones and John Kimball and Alexei I Lyapustin and Matti Mõttus and Ramakrishna R Nemani and Shilong Piao and Benjamin Poulter and Scott R Saleska and Sassan S Saatchi and Liang Xu and Liming Zhou and Ranga B Myneni},
url = {http://stacks.iop.org/1748-9326/10/i=6/a=064014 http://stacks.iop.org/1748-9326/10/i=6/a=064014?key=crossref.43f017fcdc363e1aa61c72de9125fb28},
doi = {10.1088/1748-9326/10/6/064014},
issn = {1748-9326},
year = {2015},
date = {2015-06-01},
journal = {Environmental Research Letters},
volume = {10},
number = {6},
pages = {064014},
publisher = {IOP Publishing},
abstract = {Resolving the debate surrounding the nature and controls of seasonal variation in the structure and metabolism of Amazonian rainforests is critical to understanding their response to climate change. In situ studies have observed higher photosynthetic and evapotranspiration rates, increased litterfall and leaf flushing during the Sunlight-rich dry season. Satellite data also indicated higher greenness level, a proven surrogate of photosynthetic carbon fixation, and leaf area during the dry season relative to the wet season. Some recent reports suggest that rainforests display no seasonal variations and the previous results were satellite measurement artefacts. Therefore, here we re-examine several years of data from three sensors on two satellites under a range of sun positions and satellite measurement geometries and document robust evidence for a seasonal cycle in structure and greenness of wet equatorial Amazonian rainforests. This seasonal cycle is concordant with independent observations of solar radiation. We attribute alternative conclusions to an incomplete study of the seasonal cycle, i.e. the dry season only, and to prognostications based on a biased radiative transfer model. Consequently, evidence of dry season greening in geometry corrected satellite data was ignored and the absence of evidence for seasonal variation in lidar data due to noisy and saturated signals was misinterpreted as evidence of the absence of changes during the dry season. Our results, grounded in the physics of radiative transfer, buttress previous reports of dry season increases in leaf flushing, litterfall, photosynthesis and evapotranspiration in well-hydrated Amazonian rainforests.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Resolving the debate surrounding the nature and controls of seasonal variation in the structure and metabolism of Amazonian rainforests is critical to understanding their response to climate change. In situ studies have observed higher photosynthetic and evapotranspiration rates, increased litterfall and leaf flushing during the Sunlight-rich dry season. Satellite data also indicated higher greenness level, a proven surrogate of photosynthetic carbon fixation, and leaf area during the dry season relative to the wet season. Some recent reports suggest that rainforests display no seasonal variations and the previous results were satellite measurement artefacts. Therefore, here we re-examine several years of data from three sensors on two satellites under a range of sun positions and satellite measurement geometries and document robust evidence for a seasonal cycle in structure and greenness of wet equatorial Amazonian rainforests. This seasonal cycle is concordant with independent observations of solar radiation. We attribute alternative conclusions to an incomplete study of the seasonal cycle, i.e. the dry season only, and to prognostications based on a biased radiative transfer model. Consequently, evidence of dry season greening in geometry corrected satellite data was ignored and the absence of evidence for seasonal variation in lidar data due to noisy and saturated signals was misinterpreted as evidence of the absence of changes during the dry season. Our results, grounded in the physics of radiative transfer, buttress previous reports of dry season increases in leaf flushing, litterfall, photosynthesis and evapotranspiration in well-hydrated Amazonian rainforests.
Fu, Rong
Global warming-accelerated drying in the tropics Journal Article
In: Proceedings of the National Academy of Sciences, vol. 112, no. 12, pp. 201503231, 2015, ISSN: 0027-8424.
@article{Fu2015,
title = {Global warming-accelerated drying in the tropics},
author = {Rong Fu},
url = {http://www.pnas.org/lookup/doi/10.1073/pnas.1503231112},
doi = {10.1073/pnas.1503231112},
issn = {0027-8424},
year = {2015},
date = {2015-03-01},
journal = {Proceedings of the National Academy of Sciences},
volume = {112},
number = {12},
pages = {201503231},
keywords = {},
pubstate = {published},
tppubtype = {article}
}