Water vapor and temperature inversions near the 0⁰C level over the tropical western Pacific
Date
1994
Authors
Hart, Kenneth A., author
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Journal ISSN
Volume Title
Abstract
During the Intensive Observation Period (IOP) [1 November 1992 - 28 February 1993] of the Tropical Ocean-Global Atmosphere Coupled-Ocean Atmosphere Response Experiment (TOGA COARE ). several periods of water vapor and temperature inversions near the 0°C level were observed. Satellite and radiosonde data from TOGA COARE are used to document the large-scale conditions and thermodynamic and kinematic structures present during three extended periods in which moisture and temperature inversions near the freezing level were very pronounced. Observations from each case are synthesized into schematics which represent typical structures of the inversion phenomena. Frequency distributions of the inversion phenomena along with climatological humidity and temperature profiles are calculated for the four-month IOP. Specific humidity or q inflections were observed simultaneously over large domains for extended periods of time (in excess of two days) in the midtroposphere. Local maxima in humidity were found to commonly occur near the freezing level or about 560 mb in the tropical region under study. The humidity inversions often occur in conjunction with temperature inversions (or stable layers) also at the 0°C level. The stable layer is usually positioned slightly above the moisture inversion. Two of the cases examined were observed during the active phase of the Madden-Julian Oscillation or MJO in which strong, low-level westerlies and upper-level easterlies were observed. IR satellite images of the TOGA COARE region reveal that the soundings which reflected moisture and temperature inversions at the freezing level ascended in generally clear and undisturbed conditions. During the three cases under examination, deep convection was observed in latitudinally oriented bands which formed a “double-ITCZ" structure about the equator. Frequency distributions of specific humidity inversions observed during the IOP reflect a maximum number of occurrences at altitudes just below the melting level. Distributions of stable temperature layers show a double-peak distribution - a low-level peak associated with tradewind-like or shallow cumulus clouds and a secondary peak corresponding to pressures near the 0°C level. The recurring moisture and temperature inversions near the freezing level were common enough to be evidenced in IOP averages. Climatological profiles of relative humidity averaged for the entire IOP reveal a nearly constant humidity average between 750 and 500 mb which contradicts the linear relation between relative humidity and pressure prescribed by Manabe and Wetherald (1967). The average relative humidity profiles resembled others reported in recent studies using data from the tropical western Pacific. Several mechanisms for the formation of the inversions near the 0°C level are proposed. Temperature inversions may be the remnants of stratiform rain regions which are known to produce isothermal layers just below the melting level (Findeisen 1940). Another possibility is that the temperature inversions may be the result of melting-induced, positive potential vorticity (PV) anomalies. A third explanation involves the effects of gravity waves produced by tropical cloud systems. Moisture inversions may be caused by the preferential detrainment of water vapor from cumulus clouds near stable layers. Heavily-raining congestus clouds were frequently observed by COARE ship-based radars to top out near the freezing level which may have left higher concentrations of water vapor there.
Description
Summer 1994.
Also issued as author's thesis (M.S.) -- Colorado State University, 1994.
Also issued as author's thesis (M.S.) -- Colorado State University, 1994.
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Subject
Troposphere
Water vapor, Atmospheric
Greenhouse effect, Atmospheric
Temperature inversion