Date of Award

5-1994

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean Engineering and Marine Sciences

First Advisor

Donald T. Resio

Second Advisor

John H. Trefry

Third Advisor

Hamid K. Rassoul

Fourth Advisor

Dean R. Norris

Abstract

An understanding of Earth’s natural climatic variability is essential if assessments of mankind’s impact on climate and the environment are to be made. This thesis provides information aiding in this understanding, as well as quantifies relationships between climatic variability and the environment of a specific area, South Central Florida. The environmental response studied in this thesis was drought, as the characteristics of drought are important to the economy and health of the natural environment in this region. Using statistical methods, monthly time series data spanning an 89-year period (1899-1987) representing climatic-scale, large-scale, and synoptic-scale atmospheric processes and regional-scale drought were analyzed based on a concept known as downscaling, which describes that the various scales of atmospheric processes are interrelated. Specific data sets analyzed were Northern Hemisphere Temperature Departures, Gridded Northern Hemisphere Pressure Fields, Temperature and Precipitation data for Climatic Division 4, South Central Florida, and the Palmer Drought Severity Index (PDSI) for the same division. Empirical Orthogonal Function (EOF) analysis was applied to Northern Hemisphere gridded pressure fields to determine important spatial and temporal patterns of variability in the large-scale atmospheric circulation features and to reduce the large data set to a fewer number of dimensions for time series analysis. Spectral and Fourier analysis were used to determine the periods of variability in the time series data and 12-month and 60-month data filtering schemes were used to allow trends in and relationships between data sets to be determined. Contingency table analysis/chi-squared tests were then applied to the data sets that appeared to be the most strongly related and the relationships between them were quantified. The results of this thesis show that four distinct climatic regimes existed between 1899 and 1987, with transition periods between regimes occurring in the 1920’s/1930’s, the 1950’s/1960’s, and the mid-1970’s/early 1980’s. Periods during which Northern Hemisphere temperatures were cooler than the mean were marked by the existence of large-scale circulation features characteristic of meridional atmospheric flow, while periods warmer than the mean exhibited a tendency for zonal flow patterns to exist. Periods of drier than normal conditions in South Central Florida , characterized by low precipitation amounts and low PDSI values, tended to occur during cool hemispheric periods with associated meridional flow patterns. Contingency table analysis shows that these interrelationships between cooler hemispheric temperatures, meridional circulation patterns, low regional precipitation, and regional droughts are statistically significant at the 0.1% significance level. Episodic droughts in the Indian River Lagoon area, South Central Florida, seem to exhibit a high degree of regularity, with a periodicity of about 5.5 years, with no trend of increasing or decreasing frequency found over the period studied. Further, no evidence was found linking periods of drought in this area to increases in atmospheric levels of carbon dioxide and the presumed associated increases in hemispheric temperatures.

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