Wednesday, 9 July 2014
The difference in the cloud droplet and drizzle growth processes was examined as a function of the cloud height using the CloudSat and MODIS synergetic datasets. From the CloudSat products such as 2B-GEOPROF, 2B-TAU, ECMWF-AUX, only one-layered water clouds whose top temperatures were warmer than 273K were extracted over the Pacific (20N - 50N and 120E - 180E) for JJA and DJF of three years. First, the frequency of the cloud droplet number density (Nc) and the effective particle radius (Re) were calculated for the cloud height. Nc was obtained assuming the adiabatic liquid water content from MODIS-derived cloud optical depth and Re. We found that Nc was larger for low clouds in DJF. This finding was consistent with an increase in continental-origin pollution aerosols in the winter time. Next, examining the frequency of the radar reflectivity (Ze), we found that although that of Ze was almost the same for pristine oceanic clouds regardless of the cloud height, that of polluted lower clouds was less frequent at around from -20(dBZ) to -5 (dBZ) than that of upper clouds. The region from -20(dBZ) to -5 (dBZ) approximately corresponds to drizzle particles. The less frequency of Ze at the region is consistent with the smaller Re of polluted lower clouds. Therefore, this phenomenon suggests one of the presentations for the second kind of the aerosol indirect effect.
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