Since today’s weather forecast models suffer from a poor water vapour initialisation, the general aim of this work is the assimilation of high-resolution water vapour data from state of the art lidar systems and future developments into the "Lokal Model" (LM) of the German Weather Service. The LM is a mesoscale forecast model which is currently used with a horizontal resolution of 7 km to provide 48 hour forecasts for central Europe. Because of the importance of water vapour in the troposphere, lower stratosphere, but particularly in the planetary boundary layer, it is to be expected that a clearly improved water vapour initial field will result in improved weather forecasts on all scales. In the future several lidar missions are planned by the different space agencies which will provide water vapour observations in a high temporal as well as spatial resolution with global coverage. For this purpose the infrastructure to use such valuable data sets in the forecast system of the German Weather Service should be established.

Therefore different experiments with the existing assimilation system of the LM (based on the nudging approach) and the variational system (3DVAR) which is currently under development for the global model (GME) should be carried out. If possible the more sophisticated variational system should be used as the default system because of its physically based handling of model and observation errors. First experiments using different horizontal resolutions shall be carried out with data collected during the IHOP campaign in May und June 2002 in the southern Great Plains.

With a working assimilation system available case studies for different weather situations will be performed. For example convectively active situations, frontal passages and also the development of the planetary boundary layer in undisturbed situations are of interest. Furthermore different parameterisation schemes can be tested with and without the assimilation of lidar water vapour. Later, when a larger amount of observations is available, similar situations should be examined in the forecast region of the German Weather Service to document the influence of assimilated water vapour on their forecasts.