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Variability in the hemispheric-scale atmospheric circulation can be directly linked to variations in surface environmental features, such as temperature, precipitation, salinity of water bodies, and pollutant transport. One indicator of the behavior of the hemispheric-scale circulation is the circumpolar vortex (CPV). This research utilizes a geographic information system approach to characterize variability in the Northern Hemispheric (NH) CPV. Specifically, the area, shape, and centroid of the January NHCPV are analyzed for 1959-2001 because it may provide insight about relationships between hemispheric-scale circulation and global temperature change. We also use a new means of characterizing the hemisphericscale circulation using a 'circularity ratio' (R c ). Results suggest that the January NHCPV has exhibited no long-term trends in area or shape, and that the mean centroid is positioned at approximately 85.3°N, 178.0°W. Regional patterns emerge, which suggest that the area and circularity are associated with variability in surface temperature and moist static energy. Furthermore, the area of the January NHCPV is associated with variability in the Arctic Oscillation, while the shape is tied to variability in the Pacific-North American teleconnection pattern. These results will facilitate understanding of the relationship between hemispheric-scale circulation, regional circulation, and local temperatures.

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While examining the atmospheric structure and dynamics through which the El Niño-Southern Oscillation phenomenon is associated with east African rainfall, it was discovered that circulation variability in the subtropical South Pacific Ocean has a significant but seasonally varying influence on east African rainfall receipt on interannual timescales. Enhanced equatorial east African rainfall receipt associated with El Niño events is well known to occur during the long rains from October to December, but rainfall deficits during the same season are typical of La Niña events. South Pacific circulation variability is found to enhance rainfall receipt during the October to December period, but is associated with significant east African rainfall deficits during the March to May rainy period. It is demonstrated here that outbreaks of moist South Atlantic westerly flows that are often associated with anomalous rainfall receipt over east Africa are enhanced (weakened) during El Niño (La Niña) periods.An empirical orthogonal function analysis is performed to extract the principal mode of sea level pressure variability in the tropical and subtropical South Pacific region. The time series associated with the principal mode of South Pacific circulation variability is correlated with circulation, atmospheric humidity, and outgoing longwave radiation fields during the short rains (October-December) and long rains (March-May). It is shown that South Pacific circulation variability is positively associated with east African rainfall receipt (r = 0.42, significant at the 99% confidence interval). Strengthened inflows of moist South Atlantic westerlies are associated with enhanced low-level moisture convergence, decreased lower tropospheric stability, increased cloudiness, and increased precipitable water anomalies observed during OND. Reverse circulation and hydroclimatic anomalies observed during MAM are consistent with a negative association with east African rainfall during that season; r = −0.33, significant at the 98% confidence interval.The temporal stability of these associations was tested during periods in which the principal interannual signal associated with El Niño was either very strong or very weak, and it was demonstrated that the correlations strengthened slightly (weakened markedly) during the period when the 5-year signal was very strong (weak).