Spatiotemporal Trends and Variability in the Centroid of the Northern Hemisphere's Circumpolar Vortex

Abstract

Recent previous research has established the "sharpest gradient" approach to defining the circumpolar vortex and has identified correlations of the area and circularity of the Northern Hemisphere's circumpolar vortex (NHCPV) to important atmospheric-oceanic teleconnections. However, because geographical shifts in the NHCPV, independent of area or circularity changes, could affect surface environmental conditions, this research addresses the question of the extent to which the NHCPV centroid undergoes such shifts, both intra-and inter-annually. Results show that during the 1979-2017 period, the centroid has moved less on a daily basis in more recent years, perhaps indicative of a stabilization in circulation, with annual and semi-annual periodicities in the daily distance moved. A consistent preference toward the Eastern Hemisphere is evident by the displacement of the centroids toward the Pacific basin throughout the study period. Collectively, these results indicate the mid-tropospheric response to the nearsurface warming.

Changing features of the Northern Hemisphere 500-hPa circumpolar vortex

“…To facilitate comparison of results to Bushra and Rohli ( 2019 , 2021a , b ), daily 500-hPa geopotential height data are obtained from the National Centers for Environmental Information (NCEI)/National Center for Atmospheric Research (NCAR) Reanalysis 2 project (Kanamitsu et al, 2002 ). The spatial resolution of this data set allows for delineation of longwave flow while filtering out shortwave flow, which assists in overcoming the computational challenges from daily CPV shapes perforated by cutoff lows, omega blocks, and Rex blocks (Lupo, 2021 ).…”

“…where A represents the area enclosed within the NHCPV and A c denotes the area of the circle with the same perimeter as the NHCPV on that day. Because the calculation of segment length makes R c resolution-dependent, it is important that the same data used in earlier calculations of NHCPV properties (Bushra and Rohli, 2019 , 2021a , b ) are used here.…”

“…The CPVs are positioned near the albeit discontinuous surface polar front at a given time, situated near the steepest geopotential height gradient, the sharpest gradient of air temperature, and the fastest flow of the quasi-westerly wind belt, including the polar front jet stream. Spatial features of the NHCPV area and circularity were examined by Bushra and Rohli ( 2019 , 2021a ), and the spatial and temporal features of NHCPV centroid position were described by Bushra and Rohli ( 2021b ).…”