Evaluation of Clouds and Precipitation in the NCEP Global Forecast System in Aerosol Abundant Regions/Seasons

New cloud microphysical will be implemented into the NCEP’s Next-Generation Global Prediction System (NGGPS) which aims to improve simulations of precipitation, clouds, and their interactions with aerosols. Implementation of these schemes and modifications would affect the cloud-aerosol-precipitation interactions (CAPI). It is necessary to evaluate the current forecasting data from the Global Forecast System (GFS) against observations before any CAPI effect is introduced to investigate if any model biases bear resemblance to the variations of aerosol loading and types. Extensive seasonal biomass burning aerosols over southeast Atlantic ocean stratocumulus deck is a suitable place to test the performance of the GFS simulated stratocumulus cloud when large amount of absorbing aerosols present. These absorbing aerosols absorbing can absorb incoming solar radiation, perturb the temperature structure of the atmosphere and influence the cloud cover depending on the altitude of the aerosols relative to the cloud. In our study, the impact of biomass burning aerosols on marine stratocumulus clouds has been examined in April (non-biomass burning season) and August (biomass burning seasons) using MODerate-resolution Imaging Spectroradiometer (MODIS). It is found that GFS tends to underestimate the cloud cover during biomass burning season. The smoke above clouds would strengthen the inversion and keep the boundary layer humid, leading to increased cloud cover. The downward shortwave radiation at the surface is overestimated in the GFS in the biomass burning season compared to the Clouds and the Earth’s Radiant Energy System (CERES), which is consistently with the underestimation of clouds. These results indicate the need of implementation of CAPI in the new model.