Cloud-Ocean Mixed Layer Feedback

A cloud-ocean planetary boundary layer (OPRI), feedback mechanism is presented and tested in this paper, water vapor, evaporated from the ocean surface or transported by the large-scale air flow, often forms convective clouds under a conditionally unstable lapse rate. The variable cloud cover and rainfall may have positive and negative feedback with the ocean mixed layer temperature and salinity structure. First, clouds reduce the incoming solar radiation at the ocean surface by scattering and absorption, which cools (relatively) the ocean surface layer by increasing mixed layer entrainment. The cooling of the ocean mixed layer lowers the evaporation rate, which will diminish the clouds. This is a negative feedback mechanism. Second, precipitation dilutes the surface salinity, stabilizing the upper ocean and reducing mixed layer deepening. The mixed layer may even be caused to shallow if the downward surface buoyance flux is sufficiently enhanced by the precipitation. The reduction in mixed layer depth will increase the sea surface temperature (SST) by concentrating the net radiation plus heat fluxed downward across the sea surface into a thinner layer. The increase of SST augments the surface evaporation, which in turn produces more clouds. This is a positive feedback mechanism. Fig. A shows the main physical processes (heat, mass, and momentum fluxes) at the two adjacent boundary layers; the OPBI, and the marine atmospheric boundary layer (MABI). Figure 2 illustrates this positive/negative feedback mechanism. Since clouds have significant effects on the large-scale atmospheric circulation through the transfer of heat, moisture, and momentum, and on the ocean mixed layer through the attenuation of solar radiation at the ocean surface, and since the SST is an important factor for the development of clouds, the feedback mechanism mentioned above has a potentially significant impact on the air-sea interaction, weather and ocean prediction. The Role of Clouds in Atmospheric Chemistry and Global Climate, American Meteorological Society, 39-44