School of Meteorology

Aerosol impacts on deep convective clouds: mechanism, significance, and parameterizations

Dr. Jiwen Fan
Atmospheric Sciences and Global Change Division, Pacific Northwest National Laboratory, Richland, Washington

27 February 2014, 4:00 PM

National Weather Center, Room 5600
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

Reception @ 3:30 PM

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 deep convection 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 clean to polluted environments. However, process-level modeling studies at short time scales reported both invigoration and suppression of convection by aerosols, depending on environmental conditions such as wind shear. In addition to the invigoration effect that was hypothesized previously, our recent study with a detailed bin cloud microphysical model identified another mechanism – the microphysical aerosol effect. This microphysical mechanism explains the consistent signatures of increased cloud area and top height in DCCs revealed by observations, even under conditions when invigoration of convection is absent. The atmospheric warming and surface cooling resulted from the microphysical effect buffer the thermodynamic aerosol effects on DCCs which cannot be captured in large-scale simplified-microphysics simulations. Results of the study indicate that improving cloud microphysics representation and cumulus parameterization is crucial to predict realistic climate forcing produced by increased aerosol loadings.

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