Rong Fu (UCLA) - Interaction between Aerosols and Mesoscale Convective Lifecycle Inferred from Satellite Observations

June 5, 2019 3:30pm
MS 7124

The influence of the indirect effect of aerosols on clouds and convection rests on the hypothesis that aerosols can delay precipitation and thus increase cloud lifetime. Yet, validation of this hypothesis on climate and global scale is challenging, in part due to lack of adequate observations of cloud lifecycle and strong dependence of the aerosol effect on meteorological conditions and convective lifecycle. To address this challenge, we combine observations from a suite of polar-orbital and geostationary satellites over tropical continents to infer aerosol-cloud relationships in the context of mesoscale convective lifecycles.  We also combine four different satellite sensors (CloudSat, Aura/MLS, CALIPSO, and TRMM) to capture changes of small, medium and large ice particles in convective cores and anvils and aerosol layers.  The analysis of large samples (thousands to tens of thousands) of mesoscale convective systems over the tropical continents suggest that, on global tropical and multiyear scales, moderately high aerosol loading, as inferred from the aerosol optical depth (AOD<0.3), can significantly increase ice particles of the convective cores and anvils, and prolong the mature and decay phases of the convective life cycle.  By lengthening the lifetime of the mesoscale convective systems, aerosols can substantially increase total rainfall produced during the lifetime of the convection.  Such aerosols’ invigoration effect on mesoscale convective system occurs only under the meteorological conditions that are favorable for deep convection.  This effect is also stronger for the strongest mesoscale convective systems. Under less favorable meteorological conditions and heavy pollution (AOD>0.4), increasing aerosols tends to shorten convective lifetime and reduce total rainfall produced by the mesoscale convective systems.  Thus, aerosols tend to intensify convective systems that produce floods, while suppressing the convective systems that produce medium and moderate precipitation.

Our study also shows a strong influence of convective detrainment on aerosols in the upper troposphere during the growing and mature phases of the mesoscale convection, especially over south Asian and tropical African continents.  This behavior is likely due to more and deeper convective cores with stronger vertical wind shear.