Tropospheric precursors and stratospheric warmings

Author: Judah Cohen and Justin E. Jones
December 15, 2011
Journal Article
Journal of Climate

Cohen, Judah, Justin Jones, 2011: Tropospheric Precursors and Stratospheric Warmings. J. Climate, 24, 6562–6572.

Many tropospheric Arctic Oscillation (AO) events are preceded by stratospheric AO events and even earlier in time by anomalous upward energy flux associated with Rossby waves in the troposphere. Here we identify lower tropospheric circulation anomalies that precede large AO events in both the troposphere and the stratosphere and the anomalous upward energy flux. Compositing analysis of stratospheric warming events identifies regional tropospheric precursors, which precede stratospheric warmings. The tropospheric precursor is found to vary when compositing over polar vortex displacements and splits separately.
Prior to vortex displacements the main anomaly sea level pressure center of the tropospheric precursor is located across northwest Eurasia and is associated with the Siberian high. Prior to vortex splits a similar anomaly center is identified in the tropospheric precursor but it is weaker and appears to be more strongly related to a shift in the storm tracks. Differences in the sea level pressure anomalies in the North Atlantic and the North Pacific are also observed when comparing the precursors prior to vortex displacements and splits. Identification of a unique tropospheric precursor to stratospheric warming and subsequently tropospheric AO events can help to improve our understanding of troposphere-stratosphere coupling. Furthermore, the observational evidence presented here can be compared with model simulations of winter climate variability and lead to potential model improvements.