The long-held view among atmospheric dynamicists is that the troposphere, with its abundance of mass and momentum, dominates global dynamics while the stratosphere is a more passive component, contributing little influence on tropospheric circulation. In light of recent observational and modeling studies, this view is changing as the stratosphere has been shown to contribute both directly and indirectly to the tropospheric circulation. In particular, the mid- to high-latitude troposphere is sensitive to variations in the stratospheric polar vortex related to the Arctic Oscillation (AO). We study this interaction on intra-seasonal timescales to deduce the potential mechanisms responsible for current climate trends in the mid- to high-latitude troposphere and stratosphere.

Diagnostic results and daily three dimensional maps are presented showing the structure and evolution of a typical Arctic Oscillation event. Evolution maps show a strong AO signal propagating from the stratosphere downward to the surface. Eddy-flux diagnostics are used to examine the role of eddy-mean flow interaction in inducing the anomalous winds characteristic of the AO. Anomalous zonal wind tendencies are analyzed at various heights and latitudes in conjunction with the wave driving in an attempt to attribute accelerations in the mean zonal flow to eddy forcing. The role of bandpass as well as lowpass eddies is discussed.