Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geography and Anthropology

First Advisor

Keith G. Henderson

Abstract

Trends in winter extratropical anticyclonic weather type frequencies (1961-1989) were examined for New Orleans, Louisiana, in order to identify the effects of global climatic change on regional-scale circulation changes over the central Gulf Coast. The number of days dominated by surface continental anticyclones (CH days) was found to have decreased significantly over time, while Pacific anticyclone (PH) frequency showed significant temporal increase. Therefore, 50 kPa geopotential height variability, 50 kPa geostrophic flow, and surface atmospheric variables were examined to determine whether changes in these features have accompanied the frequency changes in weather types. Prior to PH days, areas of greatest height variability were located over the subtropics. Many of these "action centers" were characterized by heights that have increased and stabilized over time. This suggests that the meridional gradient of atmospheric mass between the subtropics and extratropics may have increased prior to CH days over the Gulf Coast. Composite flow patterns during times of these extremes verified that increased zonal flow may have contributed to the relative paucity of CH events in recent years. Prior to PH days, height variance was concentrated more on the northern fringes of the subtropics than for CH height fields. The presence of a deep trough over eastern North America may not be as important in producing a PH day as in creating a CH day, but the increasing tendency for slight meridional flow over eastern North America may have advected more Pacific anticyclones to the Gulf Coast over time. This degree of amplification may not be sufficient to force continental anticyclones to the region. Collectively, these results verify that changes in continental and Pacific anticyclone frequency are linked to changes in the large-scale flow, and that atmospheric temporal and spatial scale interactions are important in winter. Some significant trends in meteorological variables during CH and PH days were found. Many of these tendencies may be related to large-scale circulation changes on CH and PH days, but others may be produced by changes in the atmosphere in general. No significant trends in the weather type intensities as a whole were identified.

Pages

192

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