Challenges Regarding the Calibration of Polarimetric X-BandWeather Radars at the Core Facility of the Jülich Observatory for Cloud Evolution

The Jülich Observatory for Cloud Evolution is developing into a Core Facility (JOYCE-CF) for monitoring cloud and precipitation processes. In western Germany the large set of instruments opperated by JOYCE-CF allow a holistic view into microphysical processes of clouds and precipitation. JOYCE-CF enables easy data access as well as instrument information for users worldwide. Information about instrument status, current projects or field campaigns and opperation procedures are provided as well. To ensure high quality data, reliable calibration of the instruments plays an important role. This paper stresses the challenge to calibrate two polarimetric X-band weather radars opperated by JOYCE-CF with respect to reflectivity Z and differential reflectivity ZDR. High accouracy in ZDR values is a challenging task as the ZDR bias varies with temperature changes at the radar site. As ZDR plays an important role in the advantage of polarimetric weather radars for estimation of precipitation type and amount, these variations in the ZDR bias are examined.