Cloud liquid water path variations with temperature observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment

Abstract

Because clouds play such a significant role in climate, understanding their responses to climatic temperature changes is essential to determining the overall impact of a given climate forcing. Cloud liquid water path (LWP) over tropical and midlatitude oceans has been observed to decrease with increasing cloud temperature. The presence of an ice sheet over the Arctic Ocean alters the energy and moisture exchange between the ocean and the atmospheric boundary layer and thus may affect the relationship between LWP and temperature. The variations of LWP with cloud and surface temperatures are examined in this paper using a combination of surface and satellite data taken during the 1998 Surface Heat Budget of the Arctic Ocean and the FIRE Arctic Clouds Experiments. The results show that LWP increases with temperature primarily because of an increase in cloud thickness that is enabled by the rise in surface moisture during the melt season. Cloud base heights and lifting condensation levels decrease as a result of the greater surface relative humidity and temperature. The average change rate of LWP with cloud temperature is 3.3% K−1, a value slightly smaller than earlier observations taken over cold midlatitude land areas. This cloud LWP feedback with temperature differs significantly from that estimated over other marine environments and should be taken into account in all climate models with explicit cloud feedbacks.