Refractivity Measurement by radar during the HYMEX Campaign

Weather radars, originally designed to detect and quantify precipitation, can be used to estimate and map the refractivity at low level, a proxy for humidity. As highlighted by previous studies, this presents a definite meteorological interest, both for numerical weather prediction and for atmospheric process studies. Recent works have given keys to perform high-accuracy measurements over operational radar without decreasing the quality of reflectivity and Doppler-wind classical measurements, and the retrieval of radar refractivity is now performed in real time with the Météo France ARAMIS operational network. Taking advantage of the HyMeX campaign (September-November 2012), refractivity measured by a few radars located in South-East France has been compared to in-situ measurement by Automatic Weather Stations, and the correlation between these two independent observations is quite good. This allows to go further in the evaluation by comparing radar measurements to refractivity from AROME and WRF numerical models. The result is generally fairly good, but differences are sometimes observed, suggesting that the assimilation of radar refractivity could improve the quality of weather forecasts. We finally illustrate the usefulness of refractivity mapping by radar, for prediction and for process studies, by showing typical meteorological cases (convection, sea breeze …) observed during the HyMeX campaign.