Observational Studies of Wave Disturbances in the Tropical Pacific and Their Relationship With Deep Cloud Activity (Global Atmospheric Research Program(garp), Fgge, Gate, Itcz, Spcz, Sst)
Tai, King-Sheng
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https://hdl.handle.net/2142/70922
Description
Title
Observational Studies of Wave Disturbances in the Tropical Pacific and Their Relationship With Deep Cloud Activity (Global Atmospheric Research Program(garp), Fgge, Gate, Itcz, Spcz, Sst)
Author(s)
Tai, King-Sheng
Issue Date
1985
Department of Study
Atmospheric Sciences
Discipline
Atmospheric Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Physics, Atmospheric Science
Abstract
First GARP (Global Atmospheric Research Program) Global Experiment, Level III-b data and the outgoing longwave radiation data are used to investigate relationships between deep cloud activity and large-scale meteorological fields from May to September in 1979. Discussion is focused on the situations in the eastern Pacific for the following reasons: (a) this is the area where strong deep convection frequently develops in the northern summer, (b) it is also an area which has been least explored meteorologically.
The monthly mean flow in July and August at 1000 mb show that the surface confluence line extends in the zone of 7-12(DEGREES)N in the eastern Pacific. The areas of convergence at 1000 mb coincide with those of the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ). The axis of the strongest deep cloud activity is colocated with the surface confluence line and their location suggest the close relationship between sea surface temperature, the ITCZ and the surface wind confluence. At 850 mb and 700 mb, easterly flow dominated most of the tropical Pacific. While, its weak latitudinal and vertical shears suggest that dry barotropic instability alone cannot account for the formation of easterly waves in the eastern Pacific.
A power spectrum analysis using Maximum Entropy Method is made for the meridional wind component at 850 mb from May through August. The waves with a period of 4-6 days are stronger in July and August than in other months, also they are active in the regions of 100-130(DEGREES)E and 130-160(DEGREES)E within the zone of 5-15(DEGREES)N. A cross-spectrum analysis between the deep cloud activity and the meridional wind indicates that deep convection occurs at or slightly behind the wave trough axis.
The structure of easterly waves, obtained by a composite technique is similar to those of African waves observed in GATE (GARP Atlantic Tropical Experiment) Phase III and easterly waves in the western Pacific determined by Reed and Recker (1971). The position of the surface confluence line shifts latitudinally with the passage of a wave is remarkably similar to that found in GATE Phase III. However, the structure in the upper level does not show distinct secondary maxima of the wave-related perturbations, which is significant with the easterly waves observed in both Africa and western Pacific.
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