The dynamical link between the troposphere and stratosphere and its potential to affect climate

The main issue of this thesis has been to increase our understanding of the mech- anisms by which the stratosphere can affect the tropospheric climate. The dy- namical coupling of tropospheric and stratospheric circulation in the Northern Hemisphere was investigated by applying the new approach Single Wave Analysis which combines a well-known theoretical concept of the coupling mechanism with the statisticai analysis of observational datasets. The isolated features were used to interpret both the coupled modes of variability in tropospheric and strato- spheric geopotential height fields and the changes in the estimated probability density function of these modes. The prominent result of this thesis is that winter seasons characterized either by an anomalously strong or weak polar winter vortex exhibit different tropospheric circulation regimes. Only in the case of a strong stratospheric polar vortex does a downward control of the tropospheric circulation by reflection of waves of zonal wave number (ZWN) one occur. This downward influence on the structure of tropospheric waves is considerably less than the influence of tropospheric dis- turbances on the structure of stratospheric waves of ZWN I and 2. This re- sult confirms our understanding of the coupling of stratosphere and troposphere: Waves in the stratosphere originate in the troposphere, whereas the disturbances in the tropospheric circulation result mainly from internal processes. However, the findings also reveal that the two circulation regimes, characterized either by an preferred exaggeration of an anomalously strong or weak polar winter vortex, exhibit different tropospheric variability structures and are of high relevance to interannual and interdecadal climate variability