Aerosol Impacts on Deep Convective Clouds: Mechanism, Significance, and Parameterizations (Invited Presentation)

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Thursday, 6 February 2014: 1:45 PM
Room C207 (The Georgia World Congress Center )
Jiwen Fan, PNNL, Richland, WA; and L. R. Leung, D. Rosenfeld, Q. Chen, K. S. S. Lim, Z. Li, J. Zhang, and H. Yan

Deep convective clouds (DCCs) play a crucial role in the general circulation, energy, and hydrological cycle of our climate system. Anthropogenic and natural aerosol particles can influence DCCs through changes in cloud properties, precipitation regimes, and radiation balance. Idealized concept model indicated an invigoration effect on DCCs by aerosols, which has been unanimously cited for explaining the observed results that consistently showed the increased cloud fraction, cloud top height and cloud thickness from the clean to polluted environments, which are at large domain over long time scale. However, process-level modeling studies at the short time scale reported both invigoration and suppression of DCCs by aerosols, depending on environmental conditions such as RH and wind shear. Our recent study over regional domains at monthly-long time duration identified an additional mechanism to the invigoration effects hypothesized previously; this microphysical mechanism explains the consistent signatures of increased cloud top area and height by aerosols in DCCs revealed by observations, even when invigoration of convection is absent. The radiative feedback resulted from the microphysical effect buffers the dynamic aerosol effects on DCCs, which can not be captured in both short-term CRM and large-scale simulations. Simulations with a two-moment bulk microphysics in CRM and microphysics convective parameterizations in large-scale models failed to produce the microphysical aerosol effect that is reported by observational studies and simulated by bin microphysics.