Tuesday, 9 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
The characteristics of precipitating low clouds are important from a variety of perspectives; from understanding why some clouds in a similar environment produce precipitation to understanding the role of precipitation organization in stratocumulus to shallow cumulus transitions. For example, prior studies have suggested larger warm clouds are more likely to produce rain because the larger thermals reduce the impacts of mixing and entrainment. With relatively sparse historical observational sampling, CloudSat and CALIPSO offer a high spatial resolution global perspective of low cloud characteristics and microphysical processes. To better understand the variability in precipitating low clouds, as well as differences from their non-precipitating counterparts, we create a warm cloud climatology by identifying oceanic contiguous cloud objects with top heights below the freezing level using the 2B-GEOPROF cloud mask and 2B-GEOPROF-LIDAR cloud fraction products from August 2006 – December 2010. Precipitating and non-precipitating clouds are separated using the 2C-PRECIP-COLUMN precipitation rate. Several warm cloud characteristics are identified including: horizontal extent, cloud top height and depth, and fraction of precipitating pixels per cloud. The thickest warm clouds reside in the tropics and subtropics, while warm clouds are shallower in the extratropics. The thickest clouds with the smallest horizontal extent are typically found in the western and central ocean basins. Conversely, regions containing the thinnest clouds with the largest horizontal extent are confined to the eastern margins of ocean basins in regions generally associated with stratocumulus. Most precipitating warm clouds are concentrated within the tropical shallow cumulus regimes and are generally larger than their non-precipitating counterparts. These initial results support the hypothesis that larger warm cumulus clouds are more likely to produce precipitation. Data will be conditionally sampled in different cloud property and environmental regimes and bivariate histograms will be analyzed to further investigate this hypothesis.
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