An Objective Procedure for Delineating the Circumpolar Vortex

Abstract

Abstract The broad‐scale, steering atmospheric circulation in the Northern Hemisphere, represented by the tropospheric circumpolar vortex (CPV), is an important driver of environmental processes. The area and circularity of the CPV are analyzed hereby delineating the leading edge of the CPV at the steepest 500‐hPa geopotential height gradient globally. The daily CPV area and circularity were aggregated to monthly averages for contrast with measurements identified in previous research for the overlapping period of record (1979–2001). Accuracy of representation of the CPV is assessed through correlations to air‐sea teleconnections known to be associated with broad‐scale, extratropical steering circulation. Correlation to monthly teleconnection indices suggests that the new method allows for improvements in the calculation of area and circularity of the 500‐hPa manifestation of the CPV. These improvements justify extension of the calculation of the standardized CPV area and circularity for the 1979–2017 period of record. Results largely mirror those for the shorter time series, with the Arctic Oscillation, North Atlantic Oscillation, and Pacific‐North American teleconnection showing stronger links to CPV area and circularity than El Niño–Southern Oscillation and Pacific Decadal Oscillation. Collectively, these results suggest that the use of a singular indicator isohypse and/or monthly averaged data to represent the CPV may oversimplify analyses, especially for identifying past and future longwave ridges and troughs. This finding is important because the amplitudes and positions of the undulations in the broad‐scale flow exert the most important impacts on variability at both low‐ and high‐frequency time periods.

Keywords

• tropospheric circumpolar vortex
• atmospheric teleconnections
• atmospheric circulation variability
• polar front jet stream