An operational tool to quality control 2D radar reflectivity data for assimilation in COSMO-DE

An operational tool has been designed to enhance the quality of 2D radar reflectivity data for assimilation in COSMO-DE within the German Weather Service (DWD). This article describes the operational algorithms including their testing, the creation of local and composite quality-index fields and their application to improve data assimilation. In the first step, algorithms have been developed and tested to define and identify some of the most severe errors in radar data: corrupt images, low-reflectivity phenomena, which occur under special meteorological conditions, spokes, rings and clutter remnants/speckles. The algorithms use simple but effective tests based on statistical and textural characteristics of spurious signals. The results are stored in an 8-bit quality-index field created concurrently with the radar data at each radar station. It contains quality flags for each individual range bin plus some header information on the overall quality of the underlying data set. The independent coding of error bits enables a differentiated a posteriori decision on whether a range bin is to be used for a given application. These local quality index fields are then used to create a radar precipitation composite, accompanied by a quality-index composite, covering Germany. This tool has now been applied operationally throughout the German radar network. As a result, the radar data quality in data assimilation could be increased.