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Convective Formation of Pileus Cloud Near the TropopausePileus clouds form where humid, stably stratified air is mechanically displaced vertically ahead of rising convection. This paper describes convective formation of pileus cloud in the tropopause transition layer (TTL), and explores a possible link to the formation of long-lasting cirrus at cold temperatures. In-situ measurements from off the coast of Honduras during the July 2002 CRYSTALFACE experiment show an example of TTL cirrus associated with, and penetrated by, deep convection. The cirrus was enriched with total water compared to its surroundings, but composed of extremely small ice crystals with effective radii between 2 and 4 m. Through gravity wave analysis, and intercomparison of measured and simulated cloud microphysics, it is argued that the TTL cirrus in this case originated neither from convectively-forced gravity wave motions nor environmental mixing alone. Rather, it is hypothesized that some combination was involved in which, first, convection forced pileus cloud to form from TTL air; second, it punctured the pileus layer, contributing larger ice crystals through interfacial mixing; third, the addition of condensate inhibited evaporation of the original pileus ice crystals in the warm phase of the ensuing gravity wave; fourth, through successive pulses, deep convection formed the observed layer of TTL cirrus. While the general incidence and longevity of pileus cloud remains unknown, in-situ measurements, and satellite-based Microwave Limb Sounder retrievals, suggest that much of the tropical TTL is sufficiently humid to be susceptible to its formation. Where these clouds form and persist, there is potential for an irreversible repartition from water vapor to ice at cold temperatures.
Document ID
20080015842
Acquisition Source
Langley Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Garrett, Timothy J. (Utah Univ. Salt Lake City, UT, United States)
Dean-Day, Jonathan (NASA Ames Research Center Moffett Field, CA, United States)
Liu, Chuntao (Utah Univ. Salt Lake City, UT, United States)
Barnett, Brian K. (NASA Johnson Space Center Houston, TX, United States)
Mace, Gerald G. (Utah Univ. Salt Lake City, UT, United States)
Baumgardner, Darrel G. (Universidad Nacional Autonoma de Mexico Mexico City, Mexico)
Webster, Christopher R. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Bui, T. Paul (NASA Ames Research Center Moffett Field, CA, United States)
Read, William G. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Minnis, Patrick (NASA Langley Research Center Hampton, VA, United States)
Date Acquired
August 24, 2013
Publication Date
January 1, 2005
Subject Category
Meteorology And Climatology
Funding Number(s)
CONTRACT_GRANT: NAG1-1505
CONTRACT_GRANT: NNG045168G
Distribution Limits
Public
Copyright
Public Use Permitted.

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