Satellite Retrieval of Marine Stratocumulus Surface Coupling State and its Effect on the Clouds Cellular Organization

Abstract:

A methodology for a complete description of the marine stratocumulus clouds geometrical and microphysical properties was developed and tested. These include, among others, coupling state and cloud geometrical depth. The methodology combines simultaneous observations from several A-TRAIN instruments (CALIPSO, CloudSat and MODIS) and re-analysis data.

Analysis of different types of Marine Stratocumulus (MSC) scenes revealed interesting features. While most of the MSC that we have analyzed existed within a coupled Marine Boundary Layer (MBL), those that existed in a de-coupled MBL, i.e., cloud layer that is de-coupled from the ocean surface, lacked the typical spatial cellular organization. It was found that the occurrence of rain within closed cells breaks and organizes them into open cells only when the clouds are coupled with the surface. Otherwise the closed cells remain as thin lightly precipitating stratiform clouds having low cloud water. The coupling state was also found to affect the ability of drizzle to break closed cells, so that closed cells in a de-coupled MBL tend to produce stronger drizzle before breaking up.

We hypothesize that rain driven downdrafts hit the surface and form gust fronts that trigger convective elements, which break the cloud deck, only when the clouds are coupled to the surface. Among the other problems that can be answered by using the presented methodology is disentangling the role of large scale meteorology and aerosols on the development of precipitation (i.e., cloud depth versus droplet concentrations as a limiting factor for drizzle initiation). Examples will be shown together with their physical interpretation.