Dehydration of the upper troposhere and lower stratosphere by subdivisible cirrus clouds near the tropical tropopause

Journal Article · Mon Apr 15 04:00:00 EDT 1996 · Geophysical Research Letters

DOI:https://doi.org/10.1029/96GL00722· OSTI ID:245188

Jensen, E J ^[1]; Toon, O B; Pfister, L ^[2]; Selkirk, H B ^[3]

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1. San Jose State Univ., San Jose, CA (United States)
2. NASA Ames Research Center, Moffett Field, CA (United States)
3. Space Physics Research Insitute, Sunnyvale, CA (United States)

The extreme dryness of the lower stratosphere is believed to be caused by freeze-drying air as it enters the stratosphere through the cold tropical troposphere. Previous investigations have been focused on dehydration occurring at the tops of deep convective cloud systems. However, recent observations of a ubiquitous stratiform cirrus cloud layer near the tropical tropopause suggest the possibility of dehydration as air is slowly lifted by large-scale motions. In this study, the authors have evaluated this possibility using a detailed ice cloud model. Simulations of ice cloud (wave periods of 1-2 hours) indicate that large numbers of ice crystals will likely form due to the low temperatures and rapid cooling. As a result, the crystals do not grow larger about 10{mu}m, fallspeeds are no greater than a few cm-s{sup {minus}1}, and little or no precipitation or dehydration occurs. However, ice clouds formed by large-scale vertical motions (with lifetimes of a day or more) should have fewer crystals and more time for crystal sedimentation to occur, resulting in water vapor depletions as large as 1 ppmv near the tropopause. The authors suggest that gradual lifting near the tropical tropopause, accompanied by formation of thin cirrus, may account for the dehydration. 15 refs., 4 fig.

• OSTI ID: 245188
• Journal Information: Geophysical Research Letters, Journal Name: Geophysical Research Letters Journal Issue: 8 Vol. 23; ISSN GPRLAJ; ISSN 0094-8276
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ATMOSPHERIC CIRCULATION
DEHYDRATION
STRATOSPHERE
TROPOSPHERE