Real-time nation-wide production of 3D wind and reflectivity fields in France: science, engineering and applications

The French Doppler radar network consists today of 24 radars, 10 of them having polarimetric capabilities. Reflectivity and Doppler volumetric data are concentrated from all 24 radar sites in real-time at the central level (Toulouse) where 3D Cartesian mosaics of covering the entire French territory (i.e. a typical 1,000 by 1,000 km² area) are elaborated.

The innovation is that the three components of the wind are retrieved nation-wide by operational combination of the radial velocities. The final product, available in real-time every 15 minutes with a spatial resolution of 2.5 km horizontally and 500 m vertically, is a 3D grid giving the interpolated reflectivity and wind field (u, v and w) values. The 2.5 km resolution arises from the fact that the retrieval is carried out every 15 minutes from radars typically spaced apart by 150 km.. Its extension to the entire European space is foreseen.

Given a high resolution 3D reflectivity and wind field as a reference, the PPIs of all radars were simulated, taking into account the scanning strategy and beam filtering effects. Comparing the retrieved field to the reference enabled to assess the efficiency of the retrieval and to optimize the parameters used in the retrieval algorithm. Quality codes will therefore be provided to give an estimate of the confidence given to the retrieval in each pixel, summarizing the number of radars actually used, the quality of the input data, the weight of the interpolation, ...

To address the problem of computing time due to the use of 24 radars, the national domain was divided into 4 overlapping sub-domains. The final product is available less than 10 minutes after all data are made available at the central level.

An experimentation is currently being held with the help of the forecasters to assess the benefit of the product in monitoring the realism of the wind structures depicted by the mesoscale numerical model.

In addition, using the polarimetric / Doppler capability of the radar, the hail content and maximum wind shear value of the cell will be assessed. Finally, a limited number of relevant parameters (echo top, maximum reflectivity, height of maximum reflectivity, Vertically Integrated Liquid Content, Hail content, wind shear) are computed and ingested in now-casting objects.