A Study of the zonally asymmetric tropospheric forcing of the austral vortex splitting during September 2002

In September 2002, the first observed austral major warming was mainly characterized by a polar vortex splitting in the middle and upper stratosphere together with an ozone hole splitting. From our synoptic investigation based on ECMWF analyses, we establish the hypothesis that lower tropospheric processes at polar latitudes are primary responsible for the vortex splitting. Over the coastline of Antarctica two regions occurred, one over the Ross shelf ice and the other over the Weddell shelf ice, where an enlarged tropospheric wave-activity generation in connection with an anticyclonic anomaly took place. The wave-activity flux was eastward and upward into the stratosphere, and was linked with an increasing ultra-long wave 2, which could be the primary reason for the vortex splitting in the stratosphere. In the troposphere, two Rossby wave trains have been identified which contribute mainly to the maintenance of the anticyclonic anomalies over both wave-activity generation regions.