Date of Award

1986

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

The diurnal patterns of hourly precipitation events in Louisiana and southeastern Texas in January have varied over space and time. Distinct spatial patterns were observed so that southern Texas had morning maximums throughout the study period while a southwest to northeast band of morning precipitation shifted south and east from eastern Texas in the 1950's into central Louisiana in the 1960's and 1970's. Southeastern Louisiana maintained an afternoon pattern throughout the period. The morning precipitation in southern Texas is the result of the diurnal variation in cyclogenesis, especially off the Texas-Gulf coast. A southwest to northeast band of mid-morning precipitation peaks is the result of the northeastward migration of weak disturbances which move to the northeast with the southwesterly flow aloft, well in advance of the Texas-West Gulf cyclone. The band of mid-morning precipitation and its associated transition zone to afternoon peaks shifted to the south and east in the 1960's and 1970's due to the more southerly displacement of the polar front. There is much evidence to support this more southerly position of the polar front, including colder temperatures across the study region, a much greater frequency of frontal overrunning rainfall events at Lake Charles in the 1960's and 1970's, and stronger winds and lower pressures aloft at Brownsville since 1958. The transition zone between morning and afternoon precipitation maximums shift to the Florida panhandle in February according to other researchers. This shift takes place because the mean position of the arctic high shifts eastward as does the axis of the arctic air outbreaks across the eastern United States. Storm tracks in the south and eastern parts of the United States are also displaced eastward in late winter and spring. This research is of interest to weather forecasters, not just in Texas and Louisiana, but also throughout much of the southern and eastern United States. Previous research of diurnal precipitation patterns has not focused on changes in diurnal patterns over time. This study indicates that diurnal patterns can shift markedly with climatic fluctuations.

Pages

139

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