An Assessment of Stratospheric Water Vapor Using a General Circulation Model. Ph.D. Thesis

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1994

OSTI ID:237291

Mote, P W

Water vapor not only participates in the radiative balance of the atmosphere and in cloud formation, it also participates in stratospheric chemistry and, due to the strong dependence of saturation on temperature, serves as a tracer for exposure of air to cold temperatures. The application of general circulation models (GCM`s) to stratospheric chemistry and transport both enables and requires a thorough investigation of stratospheric water vapor. The National Center for Atmospheric Research has redesigned its GCM, the CCM2, to enable studies of stratospheric chemistry and tracer transport, including that of water vapor. Simple methane chemistry provides an adequate representation of the upper stratospheric water vapor source in the CCM2. The CCM2`s water vapor distribution and seasonality compare favorably with observations in many respects, and the CCM2 fills gaps in the obsevations, yielding some new insights. For example, southern polar dehydration can affect midlatitude water mixing ratios by a few tenths of a ppmv. The annual cycle of water vapor in the tropical and subtropical lower stratosphere is dominated by drying at the tropical tropopause. Water vapor has a very long adjustment time, a factor 2-4 longer than for methane, a common long-lived tracer. In the lower stratosphere, however, two model deficiencies have a profound impact on simulated water vapor. The first is a cold temperature bias in the winter polar stratosphere, a deficiency common to GCM`s. The cold bias produces excessive dehydration in the southern hemisphere. This deficiency can be eliminated fairly simply by setting a minimum vapor pressure. The second deficiency, however, is not so easily remedied. Stratosphere-troposphere exchange in the tropics has a different character from the observed; for example, too little mass flux occurs under low mixing ratio conditions, so that the stratosphere is somewhat too moist.

• Research Organization: Washington Univ., Seattle, WA (United States)
• OSTI ID: 237291
• Report Number(s): N--96-22454; NIPS--96-34503
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
ATMOSPHERIC CHEMISTRY
DEHYDRATION
GENERAL CIRCULATION MODELS
STRATOSPHERE
TEMPERATURE DEPENDENCE
TROPOPAUSE
VAPOR PRESSURE
WATER VAPOR