P23     Sensitivity of microphysics parameterizations to aerosol loading.

Grell, Evelyn, CIRES, University of Colorado Boulder and NOAA/ESRL/PSD, Bao, Jian-Wen, NOAA/ESRL/PSD, Michelson, Sara, CIRES, University of Colorado Boulder and NOAA/ESRL/PSD

The local change of a hydrometeor due to perturbations in aerosol loading is a result of positive and negative processes such that the tendency for the aerosol-induced change in one microphysical process may be compensated by the response of another.  Such compensatory feedback has been discussed by, e.g., Stevens and Feingold (Nature, 2009) and Rieger et al. (Tellus, 2014), and has made quantifying aerosol impacts on clouds and precipitation very challenging.
In this study, the sensitivity of several microphysics schemes to perturbations of aerosol loading is investigated and compared in the simulation of an idealized 2-D squall line, using the Weather Research and Forecasting Model (WRF).  Analysis of the budgets for hydrometeor production and loss shows that the microphysical response to aerosol loading varies between the parameterization schemes.  While compensatory feedback may reduce the impact of the change to any individual term, it varies with the differences in microphysical process parameterizations.  A better understanding of these sensitivities may provide guidance on the relative importance of both the parameterized processes and the observational data required to evaluate and constrain them.