75 Ice Generation in Convective and Stratiform Mixed Phase Cloud over the Tropics as Observed by A-Train Satellites

Monday, 7 July 2014
Tao Luo, University of Wyoming, Laramie, WY; and Z. Wang and D. Zhang

Mixed-phase clouds have a significant impact on the global energy and water budget. However, the treatment of mixed-phase clouds in current climate models is still crude due to the poor understanding of the detailed microphysical processes in mixed-phase clouds. This study uses 4-year (2007-2010) A-Train satellite observations to understand the ice generation differences in convective and stratiform mixed phase clouds over the tropics. The radar refractivity and depolarization ratio near the cloud top (Zet and Drt) were analyzed and compared at different cloud top temperatures (CTT) among deep convective cloud (Dc), altocumulus (Ac) and altostratus (As). Compared to other cloud types, Dc has the largest Zet at all CTTs. In Dc, Drt starts to increase from 0.1 at -15oC CTT to ~0.3 at -30oC CTT, which reveals a transition from supercooled liquid dominating to ice dominating near cloud top. The Zet in non-stratiform Ac and As is larger than that in stratiform Ac and As at different CTTs. For non-stratiform Ac and As, a similar Drt transition as Dc is observed, while stratiform Ac and As show a sharp Drt transition around -35oC. These differences indicate that different ice generation and growth mechanisms should be considered according to different types of clouds in models. Moreover, the impacts of dust on ice generations in the deep convective clouds were further investigated. These observation results offer an important base to improve the model representation of microphysical properties in mixed-phase clouds.

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