Climatology of the NAO and North Atlantic hurricanes from 1950 to 2008: an analysis of physical and spatial comparisons

Deliberty, TracyTropical cyclones (TCs) are responsible for the destruction of millions of dollars in property and potentially the loss of hundreds of lives each year. Although essentially a stochastic meteorological phenomena, they owe their genesis, existence and fate to many natural modes of climate variability. As such, TCs are often subject to the larger phenomena governing them or in proximity, including but not limited to sea surface temperatures (SSTs), large-scale atmospheric circulation patterns, wind shear, and the detailed meteorological situation in the basin in which they develop. Thus, despite the independent nature of hurricanes and their course through any given basin, a large degree of their genesis and propagation results from several key factors, which allows for ease in forecasting of intensity and movement. One such factor as sea level pressure (SLP) teleconnections govern mesoscale to hemispheric weather and climate patterns, and have been shown to correlate with temperature and precipitation patterns across the globe. They are often seen responsible for fluctuations in storm patterns and movement, as is the case with the North Atlantic Oscillation (NAO). NAO, which measures the intensity between the Bermuda or Azores high and the Icelandic low, is thought to shift climate in the North Atlantic (Gray 1984). The positive phase includes a stormy Sargasso Sea (western Atlantic between Bermuda and the East Coast) with a wet East Coast and Europe when both pressure regimes are strong. The negative phase includes a southerly shifted storm flow and contrary climate when both pressure regimes are weak. Investigations into the phase relation between NAO and North Atlantic (NA) TCs have shown little or no correlation, but these studies lack detailed examination. This study aims to analyze the temporal and spatial patterns between thepositive, negative and neutral phases of NAO and NATC frequency and intensity over monthly, multi-monthly, and seasonal time intervals. NAO indices were analyzed and divided by year for the highest ten positive, negative and most neutral phase months, seasons and years. Tropical cyclones were analyzed over these multi-modal periods with chi-square analysis for the correlation of frequency and intensity. Atmospheric dynamics were also studied for spatial correspondence between NAO and NATCs, including barotropic anomalies, geopotential height, vector winds, SSTs, and SLPs. The final step involved overlaying the NATC tracks using a GIS during the studied positive, negative, and neutral phase NAO periods for spatial coincidence. No correlation between NAO and NATC frequency nor intensity during any modes is found, but the NAO seems to have a minor effect on the tracks during certain temporal modes. In other words, while no correlations are found between NAO and TC frequency or intensity, the NAO did govern the storms' movement, with more United States East and possibly Gulf Coast activity, as well as more storm tracks over the open Atlantic during positive (NAO+) phases. Storm track clustering in the Sargasso Sea, Cape Verde region, and northern North Atlantic appeared more common during negative (NAO-) phases.University of Delaware, Department of GeographyM.S