Downward coupling between the stratosphere and troposphere:
The relative roles of wave and zonal mean processes

Abstract

Many recent studies of the downward dynamic coupling between the stratosphere and troposphere have emphasized zonal mean dynamics, in relation to the Northern Hemisphere Annular Mode (NAM). The downward progression of observed zonal mean anomalies is thought to result from the interaction of upward propagating Rossby waves with the mean flow. The hypothesis of my talk will be: There are two types of stratospheric winter states, characterized by different downward dynamical interactions. In one state, most of the wave activity gets deposited in the stratosphere, resulting in strong wave-mean flow interaction, while in the other, wave activity is reflected back down to the troposphere primarily affecting the structure of tropospheric planetary waves. Observational evidence of this hypothesis will be given by comparing wave and zonal mean processes of the downward dynamical coupling between the stratosphere and troposphere. I will illustrate that downward reflection of waves (primarily of zonal wavenumber 1) is a significant component of troposphere/stratosphere dynamics in addition to NAM related processes. In addition, I will describe the basic state configuration which leads to reflection of wave 1.