Climatology of Arctic and Antarctic polar vortices using elliptical diagnostics

Abstract

The climatological structure, and interannual variability, of the Arctic and Antarctic stratospheric polar vortices are examined by analysis of elliptical diagnostics applied to over 19 yr of potential vorticity data. The elliptical diagnostics define the area, center, elongation, and orientation of each vortex and are used to quantify their structure and evolution. The diagnostics offer a novel view of the well-known differences in the climatological structure of the polar vortices. Although both vortices form in autumn to early winter, the Arctic vortex has a shorter life span and breaks down over a month before the Antarctic vortex. There are substantial differences in the distortion of the vortices from zonal symmetry; the Arctic vortex is displaced farther off the pole and is more elongated than the Antarctic vortex. While there is a midwinter minimum in the distortion of the Antarctic vortex, the distortion of the Arctic vortex increases during its life cycle. There are also large differences in the interannual variability of the vortices: the variability of the Antarctic vortex is small except during the spring vortex breakdown, whereas the Arctic vortex is highly variable throughout its life cycle, particularly in late winter. The diagnostics also reveal features not apparent in previous studies. There are periods when there are large zonal shifts (westward then eastward) in the climatological locations of the vortices: early winter for the Arctic vortex, and late winter to spring for the Antarctic vortex. Also, there are two preferred longitudes of the center of the lower-stratospheric Arctic vortex in early winter, and the vortex may move rapidly from one to the other. In the middle and upper stratosphere large displacements off the pole and large elongation of the vortex are both associated with a small vortex area, but there is very little correlation between displacement off the pole and elongation of the vortex.