Vol. 37, issue 10, article # 7

Abstract:

Two methods of delineation of the stratospheric polar vortex were compared by the main characteristics of the vortex they provide – vortex area, average wind speed at the edge, mean temperature inside the vortex. Both methods use the ERA5 reanalysis data for isobaric and isentropic surfaces, one of them is based on the geopotential and another one – on the potential vorticity (PV). Geopotential method gives higher vortex area than the PV method: 1.3 times higher for Arctic and 1.14 for Antarctic. The estimates of the average wind speed at the edge are very similar: the wind speed by PV method is 5% higher than by geopotential for the Arctic, and 3% higher in the Antarctic. Mean temperature inside the vortex by PV method is 1% lower in both the Arctic and Antarctic. The largest difference in the estimates of vortex area in the Arctic was 25.52 million km², which was reached on November 23, 2022 at the 600 K isentropic surface; and in the Antarctic it reached a value of 23.78 million km² on December 14.2. The significant difference in area demonstrates the need for careful selection of the delineation method when studying polar vortices. The significant difference in area demonstrates the need for careful selection of the delineation method when studying polar vortices.022 at the 475 K surface. The differences of vortex area are increasing with height: from 4.23 million km² at the 475 K surface to 10.24 million km² at the 600 K surface in the Arctic, from 4.91 million km² at the 475 K surface to 6.17 million km² at the 600 K surface in the Antarctic. The significant difference in areas demonstrates the necessity for careful selection of the delineation method when studying polar vortices.

Keywords:

stratospheric polar vortex, vortex delineation method, geopotential, potential vorticity

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