Dynamics of the Stratospheric Polar Vortex in 2022/2023 by Vortex Delineation Methods Using Geopotential and Potential Vorticity

Abstract

Two methods for stratospheric polar vortex delineation are compared by the main vortex characteristics they provide: vortex area, average wind speed at the edge, mean temperature inside the vortex. One of the methods is based on the geopotential, and another one is based on the potential vorticity (PV). Both methods use ERA5 reanalysis data on isobaric and isentropic surfaces. The geopotential method yields 1.3‑time higher vortex area for the Arctic and 1.14-time higher for Antarctica than the PV method. The estimates of the average wind speed at the vortex edge are very close: the wind speed by PV method is 5% higher than by the geopotential method for the Arctic and 3% higher in Antarctic. Mean temperature inside the vortex by PV method is 1% lower in both the Arctic and Antarctica. The maximal differences in the estimates of the vortex area are 25.52 million km² in the Arctic (on November 23, 2022, on the 600-K isentropic surface) and 23.78 million km² in Antarctica (on December 14, 2022, on the 475-K surface). These differences increase with the altitude: from 4.23 million km² on the 475-K surface to 10.24 million km² on the 600-K surface in the Arctic, and from 4.91 million km² on the 475-K surface to 6.17 million km² on the 600-K surface in Antarctica. The significant difference in the vortex area confirms a need in careful selection of the delineation method when studying polar vortices.