Meteorological cloud-controlling factors counteract the effects of decreased aerosols on the fraction of marine boundary layer clouds over the East Coast of the United States

Abstract:

Marine boundary layer clouds cover large areas of the oceans and strongly reflect incoming solar radiation, playing a significant role in the climate system. The effects of aerosols on the amount of these clouds are still not well documented. We analyzed long-term satellite observations and reanalysis data to understand aerosol effects on cloud amount over the East coast of the United States (ECUS) from 2003-2018. Our results confirmed the strong dependence of cloud fraction (CF) on cloud drop number concentrations (N_d) based on long-term satellite observations. Surprisingly, while N_d shows a decreasing trend over ECUS due to the reduction of anthropogenic emissions, no obvious trend in CF was revealed. We examined how changes in aerosol loading and meteorological factors contributes to long-term cloud fraction trends. Our results indicate that the effects of decreased aerosols on the fraction of marine boundary layer clouds is counteracted by meteorological cloud-controlling factors.