Comparison of Arctic and Antarctic winter-to-summer transition in the stratosphere

The characteristics of the demise of the Arctic and Antarctic polar vortices are examined with a kinematic model that advects a passive tracer on an isentropic surface using UKMO assimilated wind fields. The resulting tracer field is used to calculate effective horizontal diffusivity in the modified Lagrangian mean (MLM) framework. The effective diffusivity is found to be much larger after the breakup of the Antarctic vortex than the Arctic vortex. This indicates more vigorous mixing occurs during the Antarctic winter-to-summer transition. This mixing is accompanied by large heat transport such that the Antarctic early summer is subtantially warmer than the Arctic. Assuming the temperatures from both polar regions relax to the same radiative equilibrium state, this difference can be exploited to obtain estimates of the radiative damping time in the polar stratosphere.