Using the Weather Research and Forecasting (WRF) model coupled with a 3 spectral-bin microphysics (“SBM”) and measurements from the Atmospheric Radiation 4 Measurement (ARM) Mobile Facility field campaign in China (AMF-China), the authors 5 examine aerosol indirect effects (AIE) in the typical cloud regimes of the warm and cold 6 seasons in Southeast China: deep convective clouds (DCC) and stratus clouds (SC), 7 respectively. Comparisons with a two-moment bulk microphysics (“Bulk”) are performed 8 to gain insights for improving bulk schemes in estimating AIE in weather and climate 9 simulations. For the first time, measurements of aerosol and cloud properties acquired in 10 China are used to evaluate model simulations to better understand AIE in China. It is 11 found that changes in cloud condensation nuclei (CCN) concentration significantly 12 change the timing of storms, the spatial and temporal distributions of precipitation, the 13 frequency distribution of precipitation rate, as well as cloud base and top heights for the 14 DCC, but not for the SC. CCN increase cloud droplet number (Nc) and mass 15 concentrations, decrease raindrop number concentration (Nr), and delay the onset of 16 precipitation. It is indicated much higher Nc and the opposite CCN effects on convection 17 and heavy rain with Bulk compared to SBM stem from the fixed CCN prescribed in Bulk. 18 CCN have a significant effect on ice microphysical properties with SBM but not Bulk 19 and different condensation/deposition freezing parameterizations employed could be the 20 main reason. This study provided insights to further improve the bulk scheme to better 21 account for aerosol-cloud interactions in regional and global climate simulations, which 22 will be the focus for a follow-on paper.
Revised: January 25, 2012 |
Published: January 19, 2012