Doctor of Oceanography and Coastal Sciences (POCS)
Department of Oceanography and Coastal Sciences
This hemispheric-scale, steering atmospheric circulation represented by the circumpolar vortices (CPVs) are the middle- and upper-tropospheric wind belts circumnavigating the poles. Variability in the CPV area, shape, and position are important topics in geoenvironmental sciences because of the many links to environmental features. However, a means of characterizing the CPV has remained elusive. The goal of this research is to (i) identify the Northern Hemisphere CPV (NHCPV) and its morphometric characteristics, (ii) understand the daily characteristics of NHCPV area and circularity over time, (iii) identify and analyze spatiotemporal variability in the NHCPV’s centroid, and (iv) analyze how CPV features relate to the air-sea teleconnections that are known to explain important variability in weather/climate. Daily data (1979─2017) were collected from the National Centers for Environmental Prediction at the 500-hPa geopotential height level, and processed and analyzed in Python, MATLAB, R, and ArcGIS Desktop platform.
Results suggest that the innovative method improves the calculation of NHCPV area and circularity, proven with the significant correlations between the NHCPV and teleconnection indices. At a daily scale, both correlations and principal components analysis reveal that the NHCPV is closely related to some air-sea teleconnections. The NHCPV area has expanded linearly over the 1979─2017 period and within its four subperiods, likely because of the weakened gradient of atmospheric mass over time. On the other hand, the NHCPV has alternating periods of increasing and decreasing circularity, suggesting that it may have become more unstable in its delivery of west-to-east flow. Spectrum analysis shows distinct annual and semiannual cycles for the area and circularity over all periods. While the NHCPV centroid shifts annually and intra- annually throughout the time series, probably because of the seasonality and teleconnection linkage, the linear trend analysis shows that the day-to-day distance moved by the NHCPV centroid decreased significantly, suggesting stability in the centroid positions. Emerging hot spot analysis reveals that new and oscillating hot spots have been emerged over time. This research can be extended to understand the current and projected relationship between the full 4-D (x-y-z-t) feature-based CPV structure, ocean-air teleconnections, sea-ice forcing, and natural hazard impacts.
Bushra, Nazla, "Characterizing the Northern Hemisphere Circumpolar Vortex Through Space and Time" (2021). LSU Doctoral Dissertations. 5540.
Rohli, Robert V.
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