Improved representation of cloud-aerosol interactions in WRF-Chem parameterized convection
Preliminary testing of the modified version of WRF-Chem has been completed using observations from the US Department of Energy's Cumulus Humilis Aerosol Processing Study (CHAPS) over Oklahoma in June 2007, as well as a high-resolution simulation that was completed without the need for parameterized convection. The model shows good agreement between simulated and observed aerosol mass fractions below and within the cloud layer. The WRF-Chem simulations show instances of enhanced nitrate aerosol in the clouds that are attributable to aqueous phase chemistry and which were also seen in the CHAPS observations. The simulations are used to investigate the impact of cloud-aerosol interactions on regional scale transport of black carbon (BC), organic aerosol (OA), and sulfate aerosol. Based on our simulations, changes in the column integrated BC can be as large as -50% when cloud-aerosol interactions are considered (due largely to wet removal), or as large as +40% for sulfate in non-precipitating conditions due to the sulfate production in the parameterized shallow clouds. Simulated changes in the CDNC and in the chemical composition of cloud drop residuals are also consistent with CHAPS observations.