Wave breaking along the stratospheric polar vortex as seen in ERA‐40 data

John T Abatzoglou,Gudrun Magnusdottir

doi:10.1029/2007gl029509

Abstract

Planetary wave breaking through the depth of the Northern Hemispheric stratosphere is observed in daily ERA‐40 reanalysis data. Strong wave breaking along the vortex edge is objectively diagnosed by noting the large‐scale overturning of potential vorticity contours on isentropic surfaces spanning the stratospheric vortex. Breaking events show distinctly different climatologies depending on whether they occur along the upper or lower portion of the stratospheric vortex. During early winter there is a strong negative correlation between the frequency of breaking events in these two regions. Frequent wave breaking in the lower stratosphere in early winter appears to both shield the upper portion of the vortex from wave disturbances and reduce the net upward wave activity flux into the troposphere, thereby allowing the vortex to strengthen into mid‐winter.

Highlights

[4] Modeling studies have examined the planetary wave breaking (PWB) phenomenon in some detail
[2] The most dramatic example of nonlinear dynamics in the stratosphere is the phenomenon of planetary wave breaking (PWB)
PWB is defined as the large-scale and rapid irreversible overturning of potential vorticity (PV) contours on isentropic surfaces [McIntyre and Palmer, 1983]

Summary

Introduction

[4] Modeling studies have examined the PWB phenomenon in some detail. For example, Polvani and Saravanan [2000] showed that the presence of a strong latitudinal PV gradient in the lower stratosphere inhibits breaking at lower levels, instead encouraging vertical propagation of wave disturbances, up the vortex edge, where they amplify with height and eventually break equatorward at upper levels. [13] Lower breaking events tend to occur during the developing and decaying stages of the stratospheric vortex in early and late winter, and are less frequent in mid winter (Figure 2c).

Results

Conclusion