Development of Aerosol-CCN Activation Scheme for KIAPS-GM and the Sensitivity of Aerosol on Cloud Properties

Atmospheric aerosols play an important role in cloud formation by acting as cloud condensation nuclei (CCN). Their chemical composition and number size distribution significantly modify cloud microphysical properties and precipitation amount by altering cloud droplet number concentration, droplet effective radius, cloud albedo, cloud liquid water content, and cloud lifetime (Twomey 1974, Albrecht 1989). These microphysical changes exert a significant cooling effect at the Earth's surface to partially offset a warming effect by greenhouse gases (Lohmann and Feichter 2005). To simulate the effect of aerosols on global numerical weather prediction, we developed the aerosol-CCN activation scheme for the Korea Institute of Atmospheric Prediction System-Global Model (KIAPS-GM). KIAPS-GM is a global numerical weather prediction (NWP) system with the element-based dynamical core on cubed-sphere grids. Initial version of KIAPS-GM was developed in 2013, including the radiation, cloud macrophysics and microphysics, convection, planetary boundary layer, orographic/non-orographic gravity wave drag, and land surface. Aerosol module based on WRF-Chem/GOCART is currently being coupled into KIAPS-GM. The aerosol-CCN activation in KIAPS-GM is based on Morcrette et al. (2011) for bulk aerosol module and is based on Abdul-Razzak and Ghan (2002) and Khvorostyanov and Curry (2007) for multimodal aerosol module. To apply Abdul-Razzak and Ghan(2002) to bulk aerosol, we used the size distribution parameters (e.g., normalized number concentration, geometric mean radius, and geometric standard deviation) for each aerosol species obtained from previous observational studies. We implemented the developed scheme in KIAMS-GM to introduce diagnostic number concentrations of CCN and cloud droplet in the Weather Research and Forecasting model (WRF) Single-Moment 6-class microphysics scheme (WSM6, Hong and Lim 2006) (see the details of new WSM6 in In-Jin Choi's presentation). The sensitivity analysis is also executed with main factors affecting aerosol-CCN activation, such as aerosol mass concentration, aerosol number concentration, geometric aerosol diameter, and chemical composition, to investigate aerosol effects on CCN and cloud properties.