Development of convection in a mesoscale cloud system and its effect on the microphysics over the tropical Atlantic Ocean

Climate models have large uncertainty to represent the low clouds in the transitional zone from stratocumulus to cumulus clouds. This talk presents an observational study of a mesoscale cloud system near Ascension Island during the CLouds and Aerosol Radiative Impacts and Forcing (CLARIFY) field campaign. Extensive aircraft measurements were made to investigate the cloud microphysics when convection developed in a stratiform cloud system. The aircraft penetrated the clouds at levels below, within, and above the main layer. In-cloud penetrations show that the development of convections increased the drop number concentration, the effective radius of drops, the size of drizzle drops, and liquid water content. In the process of convection development, the morphology of the cloud changed from an overcast stratocumulus system to organised convective clouds. The wind shear and the compensating subsidence associated with the convections seemed to be responsible for the appearance of the system. The results indicate that the convective clouds significantly affected the stratocumulus cloud properties in the transition. Our study of the microphysical processes in the transitional zone helps to improve the representation and evolution of low clouds in models.