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Revised identification of tropical oceanic cumulus congestus as viewed by...

Casey, S. P. F., E. J. Fetzer, and B. Kahn (2012), Revised identification of tropical oceanic cumulus congestus as viewed by CloudSat, Atmos. Chem. Phys., 12, 1587-1595, doi:10.5194/acp-12-1587-2012.

Congestus cloud convective features are examined in one year of tropical oceanic cloud observations from the CloudSat/CALIPSO instruments. Two types of convective clouds (cumulus and deep convective, based on classification profiles from radar), and associated differences in radar reflectivity and radar/lidar cloud-top height are considered. Congestus convective features are defined as contiguous convective clouds with heights between 3 and 9 km. Three criteria were used in previous studies to identify congestus: (1) CloudSat and CALIPSO cloud-top heights less than 1 km apart; (2) CloudSat 0 dBZ echo-top height less than 1 km from CloudSat cloud-top height, and (3) CloudSat 10 dBZ echo-top height less than 2 km from CloudSat cloud-top height. A majority of congestus convective features satisfy the second and third requirements. However, over 40 % of convective features identified had no associated CALIPSO cloud-top height, predominantly due to the extinguishment of the lidar beam above the CloudSat-reported convective cloud. For the remaining cells, approximately 56 % of these satisfy all three requirements; when considering the lidar beam-extinction issue, only 31 % of congestus convective features are identified using these criteria. This implies that while previous methods used to identify congestus clouds may be accurate in finding vigorous convection (such as transient congestus rising toward the tropopause), these criteria may miss almost 70 % of the total observed congestus convective features, suggesting a more general approach should be used to describe congestus and its surrounding environment.

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