Estimation of water cloud properties from satellite microwave, infrared and visible measurements in oceanic environments. 2. Results

Abstract

A microwave (MW) method for deriving cloud liquid water path (LWP) and cloud water temperature (Tw) is validated by using soundings and results from a visible (VIS) and infrared (IR) retrieval method. The two retrieval methods are combined into a single technique. MVI (microwave, visible, and infrared), to estimate the frequency of multilayered clouds and the effective droplet radius re in water clouds. These techniques were applied to Meteosat and special sensor microwave/imager (SSM/I) data taken during June 1-28, 1992, over the Atlantic Stratocumulus Transition Experiment (ASTEX) region. For low clouds, as identified with the VIS-IR method, Tw on average is nearly the same as the VIS-IR cloud-top temperatures (Tc). A negative correlation between LWP and Tc was found for the clouds. For midlevel clouds, Tw is about 8K warmer than Tc because of either large cloud thicknesses or multilayered clouds. When high clodus are found by the VIS-IR method, Tc is ~30K colder than Tw, indicating that lower-level liquid-water clouds may be detected by the MW method. On the basis of the matched Tw and Tc obsevations, the estimated frequencies of multilayered high, middle, and low clouds are about 36%, 19% and 0%, respectively, values that are similar to cloud radar measuremetns. Matched satellite and ground-based radar data show that the MVI technique can separate cloud layers when high ice clouds overlap lower liquid water clouds. The distributions of re for water clouds are about the same for low, middle and broken clouds with mean and standard deviations of ~12 and 10μm, respecitvely. The frequency of large droplets (re>16 μm) suggests that drizzle occurs in ~30% of the matched Meteosat-SSM/I cloudy conditions.