An objective determination of the polar vortex using Ertel's potential vorticity

Abstract

Abstract. We have developed objective criteria for choosing the location of the northern hemisphere polar vortex boundary region and the onset and breakup dates of the vortex. By determining the distribution of Ertel's potential vorticity (Epv) on equivalent latitudes, we define the vortex edge as the location of maximum gradient of Epv constrained by the location of the maximum wind jet calculated along Epv isolines. We define the vortex boundary region to be at the local maximum convex and concave curvature in the Epv distribution surrounding the edge. We have determined that the onset and breakup dates of the vortex on the 450 K isentropic surface occur when the maximum wind speed calculated along Epv isolines rises above and falls below approximately 15.2 m s-•. We use 1992-1993 as a test case to study the onset and breakup periods, and we find that the increase of polar vortex Epv values is associated with the dominance of the term in the potential vorticity equation involving the movement of air through the surface due to the diabatic circulation. We also find that the decrease is associated with the dominance of the term involving radiatively induced changes in the stability of the atmosphere.

Chemical ozone loss in a chemistry‐climate model from 1960 to 1999

“…The vortex edge was determined as the equivalent latitude, where the gradient of potential vorticity with respect to f was largest and near the maximum zonal wind [Nash et al, 1996]. We did not correct for a linear trend of 1.3°(not significant at 95% confidence level) found in the vortex edge determination.…”

Dynamic variability of the Asian monsoon anticyclone observed in potential vorticity and correlations with tracer distributions

“…[4] The behavior of the anticyclone as a large-scale PV anomaly linked to enhanced tracer gradients is reminiscent of the stratospheric polar vortices [e.g., Butchart and Remsberg, 1986;Nash et al, 1996;Manney et al, 2009;Santee et al, 2011]. A useful diagnostic to study the development and confinement of the polar vortices is provided by the time variations of the area enclosed by specific PV isolines.…”

An assessment of southern hemisphere stratospheric NOx enhancements due to transport from the upper atmosphere

“…To analyze the HALOE data in detail and to know exactly where the data are taken relative to the polar vortex, we use equivalent latitude (latcq) coordinates as described by [Nash et al, 1996]. Briefly, they define the vortex edge based upon the maximum in the PV gradient (A(latcq) = 0 in this paper) and also a boundary region around this edge based upon the inflections in the PV field (generally A(latcq) • +5).…”