Flugzeuggetragene Wasserdampf-Lidarmessungen im Subtropenjet im Vergleich mit ECMWF-Modelldaten

Kurzfassung

During the transfer flights of the meteorological research aircraft Falcon run by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR) in November and December of 2005 from Oberpfaffenhofen, Germany to Darwin, Australia for the SCOUT-O3 campaign (Stratospheric-Climate Links with Emphasis on the Upper Troposphere and Lower Stratosphere) a DIAL (Differential Absorption Lidar) measured the water vapour mixing ratio and in-situ board instruments measured the wind speed. For the investigation of the meteorological processes in the area of the subtropical jet and the polar front jet, data at a distance of about 7000 km over the Mediterranean Sea, the Arabian Peninsula and the Arabian Sea is used. As the crossed part of the subtropics is a data-sparse region there are less routine measurements of meteorological parameters to be assimilated in weather prediction and climate models. In order to investigate the deviation between the global atmospheric model of the ECMWF in the version TL511L60 and the measurements they were compared to the analysis data of the weather prediction model, which is interpolated onto the flight path of the measurements. The calculation of backward trajectories gives information about the origin of the observed air masses and helps in understanding the processes in the subtropics where air masses with a different amount of water vapour are transported by the atmospheric circulation in South-North-direction and in understanding how the subtropical jet which transports air in West-East-direction impacts the pattern of the water vapour. The comparison of the wind speeds showed a underestimation in the model of the wind speeds in the jet streaks of an average 6 % whereas the borders of the jet stream were overestimated by the global model by up to 7 m/s compared with the measurements. The water vapour mixing ratio has very small values in the upper troposphere and the lower stratosphere. This is why the relative deviation has values of up to 100 % in some areas. Most of the time the deviation is lower than 50 %. In the comparison of the measurements and the model very similar patterns are seen, whereby the model tends to be too dry in the upper troposphere and lower stratosphere. On the other hand the model overestimates the water vapour in the lower troposphere by average 30 %. Small scale changes in the water vapour and the wind speed and large gradients cannot be depicted in the model due to the coarse model grid. Sometimes the patterns are spatially shifted. As the deviations are often present in the vicinity of large gradients it can be expected that an improvement of the grid resolution will lead to lower deviations. This thesis shows that large scale meteorological processes like the subtropical jet stream and the Hadley-Cell, as well as small scale processes like intrusions and filaments of water vapour are well depicted in the model.