Observed and Modeled Dominant Cloud Controlling Factors over the Global Oceans

In an effort to identify dominant cloud controlling factors in the extratropics, daily cloud fraction data from different satellite platforms are examined in conditions of low-level clouds, subsidence and upward surface sensible heat fluxes. The relationship between low-level cloud fraction and a series of environmental metrics is explored over the global oceans. We constructed and will present a novel map of dominant cloud controlling factors and discuss its implications. We will show that the dominant controlling factor for cloud fraction changes with location. In the subtropics, our map reveals that the dominant cloud controlling factor in the stratocumulus regions is the potential temperature contrast between the surface and 800 hPa (so called cold air outbreak parameter M), but EIS and SST also play a dominant role. In the rest of the subtropics, 10-m winds dominate. In the extratropics, the sensible heat fluxes dominate in the winter time western boundary current regions, and this influence extends into the more subtropical sea surface temperature front regions in the southern oceans. Elsewhere, and more specifically at high latitudes, the estimated inversion strength dominates.

We will discuss the impact of seasonal variations, especially in the northern hemisphere, as well as diurnal variations. We will also discuss the impact of using different time periods and instruments. We will then present similar maps for liquid water path. Finally, the maps of dominant cloud controlling factor for both cloud fraction and liquid water path obtained using output from the GISS Earth System Model will be contrasted to those observed, and their potential for model evaluation demonstrated.