Algorithm for comparing stratospheric polar vortex delineation methods based on geopotential and potential vorticity on isopotential surfaces
E.A. Sidorovski1, A.V. Pavlinsky1, V.V. Zuev1, V.V. Gerasimov2
1Institute of Monitoring of Climatic and Ecological Systems of the Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia
2V.E. Zuev Institute of Atmospheric Optics of Siberian Branch of the Russian Academy of Science, Tomsk, Russia
Keywords: stratospheric polar vortex, vortex delineation method, geopotential, potential vorticity, ERA5
Abstract
Studying the characteristics and dynamics of stratospheric polar vortices requires the correct determination of their edges. Polar vortex delineation methods are mainly based on the values of potential vorticity (PV) or geopotential (GPT). The problem in directly comparing the PV and GPT methods is that the former determines the vortex edge on isentropic surfaces, while the latter does it on isobaric ones. In this paper, we present an algorithm developed to adequately compare the results of polar vortex delineation by these methods. The algorithm is based on projecting the vortex edges onto isopotential surfaces (i.e., surfaces of constant geopotential height), same for both methods. Application of the algorithm to delineating the 2019 Antarctic polar vortex showed, in particular, the following: (1) during the period of the vortex stable state (June 1 - August 31), its area on isopotential surfaces estimated by the GPT method exceeds the area estimated by the PV method by 16.17-21.20 million km2 in the range of geopotential heights 20.89-24.37 km, respectively; (2) the dynamics of the vortex edge and area estimated by both methods are generally similar, but the vortex edges obtained by the GPT method are smoother, and the strong irregularity of the vortex edges obtained by the PV method leads to abrupt changes in the vortex area. The algorithm will be useful in studying the dynamics of polar vortices from the beginning of their formation to the moment of breakup in both hemispheres.
|
