Operational monitoring of radar differential reflectivity using the sun

The issue of the differential reflectivity calibration is crucial for successful applications of dual-polarization radara. Offline sun measurements, where the operational scanning is stopped and the radar antenna is pointing at the sun, are generally employed to calibrate the polarimetric receiving chain. In the literature the use of dedicated sun scans for monitoring the differential reflectivity calibration on the polarimetric WSR-88D radar and the required corrections for differences in the noise power and bandwidths between the horizontal and vertical channels have been described.

Recently an "online" sun method has been developed by Holleman and Huuskonen, where incidental sun hits are automatically detected in polar volume data generated during operational scanning, for monitoring the antenna pointing at low elevations and the weather radar receiving chain. The method is suited for routine application and it has been validated using offline sun tracking experiments.

Here we present an extension of this online method towards monitoring of the differential reflectivity on polarimetric weather radars. Operational volume data from polarimetric weather radars in Trappes (Meteo France) and in Bornholm (Danish Meteorological Institute) were employed for this study. The solar method can be used for monitoring of the day-to-day stability of the polarimetric receivers and for a comparison with the results from a rain calibration perforemd at zenith. In the presentation we will introduce the online sun method and show results from the French and Danish polarimetric radars.