6.3 Long-term CRM Simulations of Aerosol-Convection Interaction in the Tropics

Wednesday, 9 January 2013: 4:30 PM
Room 5ABC (Austin Convention Center)
Derek J. Posselt, University of Michigan, Ann Arbor, MI; and E. L. Dagg and S. M. Saleeby

Aerosol effects on cloud albedo and lifetime in tropical cumulus, stratocumulus, and isolated deep convective clouds have been extensively studied in recent years. However, the majority of tropical precipitation and cloud radiative forcing is produced by organized clusters of convective systems. Deconvolving the effect of aerosol on tropical MCSs is challenging because these cloud systems interact strongly with their dynamic and thermodynamic environment. Recent idealized experiments indicate aerosols exert a non-trivial influence on both the properties of organized deep convection and their interaction with the surrounding environment.

In this presentation, aerosol influence on deep convective cloud systems is examined using long-term (30-60 day) CRM simulations of convectively active time periods driven with observed large scale temperature, water vapor, aerosol concentrations, and winds. Sensitivity experiments are conducted, in which aerosol concentration is systematically increased over the length of each simulation, and the results are examined to determine how changes in aerosol concentration affect the integrated cloud radiative effect, as well as the mesoscale dynamics and interaction with the cloud-free environment. Our results to date suggest the following. Consistent with previous findings, increases in aerosol concentration lead on average to larger (smaller) cloud droplet (rain drop) number and mass. Similarly, there is a dynamic effect, in which both updrafts and downdrafts are stronger in high-aerosol environments. Total precipitation increases in high aerosol environments, but the vertical distribution of liquid and ice, and associated radiative heating rates, changes in a non-monotonic fashion, indicating complexity in the integrated convection-aerosol interaction. We will present a detailed analysis of the convective structure and aerosol cloud interaction and discuss implications for the role of aerosol-convection interaction in the climate system.

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