The circulation patterns of the middle atmosphere are mainly caused by the action of waves of different dimensions. While planetary Rossby waves influence the dynamics of the stratosphere, the meospheric dynamics depends sensitively on gravity waves. An important example for the interaction between waves and mean flow are sudden stratospheric warmings, the topic of the matrix group.
The first midwinter stratospheric warming was observed by Richard Scherhag in Berlin in 1952 who accounted this huge temperature increase to a measurement error. Today we know, that sudden stratospheric warmings occur almost every arctic winter with different intensity. They also effect the abovelying mesosphere and the underlying troposphere and therefore our weather.
There are two crucially things necessary for the classification of stratospheric warmings as a final warming: 1.) the temporal occurance between March and May and, 2.) the final wind reversal from westerly wind in winter to easterly wind in summer. Thereby the reference is the zonal mean zonal wind at 60° N at 10 hPa (~32 km). In spring 2016 the transition of the stratospheric zonal wind from westerly wind to easterly wind already occurred at the beginning of March while in the mesosphere the final transition occured about 4 weeks later. This unusual phenomenon of a mesospheric late winter is currently studied in the matrix group with a close cooperation of observations and theory.
Speaker: Dr. Ch. Zülicke