Utilisation of radar information to refine precipitation fields by a variational approach

A new method for precipitation downscaling by utilizing radar information is presented. High resolution spatial patterns of the radar information are introduced with a variable weight into an analysis, based on direct station observations. Results of the first application of this approach using radar data are presented for a case study as well as for analytical fields showing the improvement of the analysis quality. Furthermore it can be shown that the weight for the radar information is generally lower than unity and varies considerably over the domain. This means that there is usually a significant difference between the precipitation amount in the lowest volume seen by radar and observed by rain gauges at the ground. The advantage of the proposed method is the simple mathematical approach and the relative inexpensive computational effort.