Theoretical and Modeling Studies of The Marine Planetary Boundary Layer

SCIENTIFIC BACKGROUND AND RESEARCH GOALS: We do not currently understand what determines the fractional cloudiness in partly cloudy boundary layers, how it is influenced by cloud-top entrainment instability (Randall, 1980), or what controls the transition from stratocumulus to cumulus conditions. These questions have a direct bearing on the radiation budget at both the top the atmosphere and the sea surface, and also on the entrainment rate (Randall, 1987). The importance of boundary-layer clouds stems, to a large extent, from their powerful influence on the net radiation at the sea surface. They block incident solar radiation (with albedoes up to about 50 % ) and at the same time emit downward strongly in the infrared. Their net effect on the surface energy budget is believed to be a strong reduction in the energy absorbed by the ocean (e.g. Esbensen and Kushnir, 1981). Despite the obvious importance of this effect for the thermal structure of the upper ocean, very little is known about-the coupling between the ocean mixed layer with boundary layer clouds. The coupling can work in both directions; the sea surface temperature strongly influences the type and amount of boundary-layer cloud, while large cloud amounts are favored where the sea surface temperature is low (e.g., Hanson, 1990)