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Hung-I Lee (UCLA), Monsoon Onset and...

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Upcoming Seminar

Hung-I Lee (UCLA), Monsoon Onset and Precipitation Control by Mid-Latitude Waves in Modern and Glacial Climates

Wed, Apr 24, 2019

MS 7124

Monsoons are now increasingly considered seasonal and local migrations of the IntertropicalConvergence Zone (ITCZ). However, the East Asian and North American monsoonsextend well into the subtropics and midlatitudes and do not feature a well-defined crossequatorialflow, thus indicating that this well-adopted theory may be inadequate. Becauseof its importance to humanity, predicting monsoon onset remains a pressing goal of modernmeteorology. From a global space-time diagram of column water vapor (CWV) at 30Nlatitude from daily reanalysis data, we found two longitude-origin of atmospheric rivers(LOARs) that feature locally enhanced CWV and evolve from the Eastern Pacific/Atlanticbasins in the winter to the Western Pacific/Atlantic in the summer. East Asian SummerMonsoon (EASM) onset coincides with the time CWV in the Pacific LOAR first exceeds40 mm, which also typically occurs just before it makes landfall. LOARs exist in 39-year(1979-2017) daily climatological mean CWV, demonstrating the seasonal cycles of these featuresare quasi-stationary and potentially useful for monsoon onset prediction. EASM onsetis particularly predictable following El Niño Southern Oscillation (ENSO), consistently occurringone month after the LOAR crosses the dateline. Simplified GCM experiments anda semi-empirical theory reveal a plausible mechanism of LOAR formation, thus opening anew window into seasonal-scale prediction of subtropical monsoon extensions.The impotance of mid-latitude waves on monsoon precipitation distribution is also observedduring Last Glacial Maximum (LGM, 21ka) climate and leads to moistening of theLGM American Southwest. Here, we compare a synthesis of pollen proxies of precipitationduring Last Glacial Maximum (LGM, 21ka) over North America to constrain the PaleoclimateIntercomparison Model Project (PMIP3) ensemble. In model simulations that comparefavorably with proxy synthesis, we find a strong correlation between monsoon precipitationand meridional wind anomaly, suggesting the patterns are mainly governed by stationarywave forcing. The major perturbations of meridional wind anomaly under LGM consist of topographicforcing due to rising elevation from the Laurentide ice sheets and thermodynamicforcing due to alteration of the mean state from albedo change. Weak stationary waves andwesterlies are generated by models with favorable comparison to the proxy synthesis.

Tersi Arias	Graduate Student	tersiarias [at] atmos.ucla.edu
Nathaniel Brockway	Graduate Student	nwbrock [at] atmos.ucla.edu
Jie Rou Chen	Graduate Student	jchen [at] atmos.ucla.edu
Tomas Chor	Graduate Student	tomaschor [at] atmos.ucla.edu
Chris Collimore	Graduate Student	cccollimore [at] atmos.ucla.edu
Daniel Dauhajre	Graduate Student	ddauhajre [at] atmos.ucla.edu
David Gonzalez-Martinez	Graduate Student	dhgonzalez89 [at] ucla.edu
Matthew Grieco	Graduate Student	mgrieco [at] atmos.ucla.edu
Julia Hazel	Graduate Student	jhazel [at] atmos.ucla.edu
Dial Hoang	Graduate Student	dhoang [at] atmos.ucla.edu
Yue Huang	Graduate Student	yhuang [at] atmos.ucla.edu
Yi-Hung Kuo	Graduate Student	yhkuo [at] atmos.ucla.edu
Hung-I Lee	Graduate Student	hilee [at] atmos.ucla.edu
Sydnie Lemieux	Graduate Student	slemieux [at] atmos.ucla.edu
Matthew McKinney	Graduate Student	mmckinney [at] atmos.ucla.edu
Jordyn Moscoso	Graduate Student	jmoscoso [at] atmos.ucla.edu
Victor Pinto	Graduate Student	vpinto [at] ucla.edu
Dilhara Ranasinghe	Graduate Student	dilharar [at] atmos.ucla.edu	BH 9277
Aviv Solodoch	Graduate Student	asolodoch [at] atmos.ucla.edu
Wu Sun	Graduate Student	wu.sun [at] ucla.edu	MS 7221
Katie Tuite	Graduate Student	ktuite [at] atmos.ucla.edu
Francis Turney	Graduate Student	fturney [at] ucla.edu
Boyi Wang	Graduate Student	bywang [at] atmos.ucla.edu
Ken Zhao	Graduate Student	kzhao [at] atmos.ucla.edu

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