Graduation date: 1988 / Figures in original document are black and white photocopies. Best scan available.

A diagnostic modeling study of the cloud and precipitation processes, and also frontogenesis have been analyzed in a severe narrow cold-frontal rainband with the aid of a three-dimensional, diagnostic cloud model. The results of the model simulations indicate that the heavy precipitation just behind the surface cold front was associated with a low-level warm rain process driven by the severe prefrontal updraft. The precipitation well behind the leading edge of cold front resulted from the melting of graupel. The sensitivity studies for the rain water distribution indicated that the Analytical Gamma distribution may be a more suitable functional fit for the raindrop distribution as compared with the Marshall-Palmer distribution. The differential heating due to microphysical processes (condensation and evaporation) at the leading edge of the surface cold frontal region facilitated the required density contrast across the front and thus maintained the propagation of the density current. The leading edge of the cold front was also characterized by frontogenesis for levels above 0.9 kin and frontolysis just ahead and immediately behind the cold front. The low level frontolysis indicated that buoyancy effects were almost negligible at the leading edge of the cold front. Instead the upward motion was created by mechanical lifting (pressure effects). The frontogenetical effects due to diabatic heating were quite important at the 1.2 - 2 km levels where the peak updraft occurred. / Graduation date: 1987

Thesis (M.S.)--University of Wisconsin--Madison, 1983. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 127-130).

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Squall lines possessing nearly all the characteristics of tropical squall lines occasionally develop during the summer monsoon over southern Arizona and northwestern Mexico. Initial thunderstorm formation is over the mountains along the Continental Divide in the late afternoon. Satellite imagery, cloud-to-ground lightning strike data, and surface observations indicate the squall lines move from east to west or northeast to southwest by discrete propagation faster than all the winds below 20 kPa so that most of the anvil clouds lag behind. The synoptic-scale circulation is anomalous with a strong ridge located over the western United States and a deep trough located over the eastern United States. West to northwest winds are found in the boundary layer over southern Arizona and northwest Mexico while a deep layer of east winds are observed above. As a result, most of the environmental wind shear is confined to the lowest 2.5 km above the ground. The low-level wind shear seems to be required for the westward propagation of thunderstorms and the formation of the squall lines. Extremely dry midtropospheric air develops in the easterly flow through some combination of advection and subsidence and also appears to be an important factor in the development of the squall lines. A two-dimensional, nonhydrostatic, numerical model was able to simulate many of the features observed in these squall lines. Solar heating of the elevated terrain in the model caused the initial thunderstorm to develop over the Continental Divide. Continued development of new thunderstorms to the west of the Divide produced a squall line that travelled westward by translation of cells and discrete propagation, wherein new cells would develop 10-25 km ahead of the old ones, at a speed greater than all the winds below 30 kPa. Upward motion produced by westward propagating gravity waves and by the strong low-level convergence found just ahead of the gust front appeared to cause several episodes of discrete propagation. The creation of horizontal potential temperature gradients and the vertical and horizontal advection of preexisting vorticity gradients combined to produce the vorticity field associated with the rear inflow jet that developed beneath the simulated squall line.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (p. [120]-126).

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Meteorology, 1979. / Microfiche copy available in Archives and Science. / Bibliography : leaves 82-83. / by Frank Parker Colby, Jr. / M.S.