The short-term dynamic influence of the stratosphere on the troposphere during Northern Hemisphere winter

A downward influence from the stratosphere to the troposphere occurs by a downward propagation of zonal mean wind anomalies from the middle atmosphere into the troposphere due to wave-mean flow interaction. This leads to a change in the meridional wave propagation in the troposphere. To understand processes involved in this mechanism in more detail, a statistical-dynamic approach was applied to Northern Hemisphere observational data. This multivariate Single Wave Analysis (SWAN) is used to isolate - on a hemispheric scale - the vertical propagation of ultra-long spherical wave-like anomalies and the relationship between the strength of the stratospheric polar winter vortex and mid-tropospheric waves. The results show that a significant linear influence of the strength of the stratospheric polar vortex on the waves of zonal wave number (ZWN) 2 and 3 in the mid-troposphere exists. For waves of ZWN 1 nonlinear effects dominate because different propagation characteristics for these waves are observed under strong and weak polar vortex conditions. The results are used to evaluate atmospheric general circulation models.