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In order to minimize the economic and social impact of hazardous weather in the Alps, three X‐band dual‐polarization radars were deployed in the southeast of France during the RHYTMME project in 2011–2013 and more recently have been incorporated formally into the conventional radar network already operating S‐ and C‐band radars. In this mountainous region, the radars' beam shielding by the complex terrain, the very different altitudes of the radars, the significant attenuation at X‐band and the low density of rain‐gauges have made the integration of these radars into the operational service a challenging exercise. In this article, the framework used to evaluate the corrections applied to the volume data produced by the radars is presented and the residual errors related to the partial beam blockages, the attenuation by rain, the wet radome, and the melting layer are carefully studied and disentangled. The results of the analysis suggest that: (a) the beam blockage correction requires the use of a much higher resolution digital elevation model (DEM) in mountainous regions than the 250 m resolution DEM currently uses, (b) the dual‐pol reflectivity (Zh) attenuation correction used at Météo‐France performs well in the rain but the differential attenuation on Zdr is overestimated, (c) the attenuation of wet snow is underestimated and a mean error of 2 dB is induced by the melting layer in spring and autumn, (d) the wet radome, as well as producing significant attenuation on Zh, induces differential attenuation on Zdr. The attenuation in the melting layer is further investigated taking advantage of the height difference between the radar sites. A new specific attenuation coefficient for wet snow is suggested and it is shown to reduce the seasonal bias on three particular events observed in spring and autumn. Dual polarimetric X‐band radars have been considered as a promising solution to fill gaps in radar networks over mountainous regions. The quantitative estimation of precipitation from these radars is subject to various error sources. Based on comparisons of co‐located radars observations, this study presents a quantitative error assessment of (a) the beam‐blockage correction, (b) the attenuation correction in the rain layer, (c) the wet radome attenuation correction and (d) the attenuation correction in the melting layer. [ABSTRACT FROM AUTHOR]

The ability to perform multiple-Doppler wind synthesis from operational weather radar systems on an operational basis has been investigated by the French Weather Service since 2006 using a (sub-)network of six Doppler radars covering the Greater Paris area. This analysis has been recently extended to the entire French radar network so as to implement a nationwide, three-dimensional reflectivity and wind field mosaic to be eventually delivered to forecasters and modellers, as well as automatic nowcasting systems for air traffic management purposes. In this composite analysis, data collected by all 24 radars of the French radar network are collected, pre-processed and combined in real time at intervals of 15 minutes to retrieve the complete wind vector ( u, v, w) and reflectivity fields at a horizontal resolution of 2.5 km within a domain of approximately 1000 × 1000 × 12 km3. In order to illustrate the performance of this new product, examples of 3-D wind and reflectivity output produced during the passage of two significant weather events are presented: the extratropical storm Klaus, which struck France on 24 January 2009 with hurricane-force gusts, and a typical orographic high-impact precipitation event that developed on 21 October 2009. The evaluation of real-time radar outputs against operational analyses attests to the consistency of the retrieved wind fields. [ABSTRACT FROM AUTHOR]

This article presents the evaluation of several polarimetric quantitative precipitation estimation (Pol-QPE) algorithm candidates for operational implementation in the Météo-France polarimetric weather radars (nine C-band and one S-band out of a total of 24 radars in 2011). Since the performance of the algorithms depends on both the quality of the polarimetric variables and the applied polarimetric processing, the article first describes the current polarimetric processing chain and then provides a comprehensive analysis of the quality of the polarimetric variables. Three types of QPE algorithms have been studied at C-band in ideal conditions (short ranges, no partial beam blocking, no vertical profile of reflectivity effects): (i) algorithms based on simple Z-R relationships with and without attenuation correction using the differential phase Φ d p, (ii) an algorithm based on reflectivity ( Z h) and differential reflectivity ( Zd r), and (iii) algorithms based on specific differential phase ( K d p). Evaluation against rain-gauges, performed hourly, confirms the superiority of polarimetric algorithms as repeatedly reported in the literature. It also shows that the benefits brought by algorithms based on power variables, Z h and Z d r, are critically dependent upon the capability to correctly calibrate them. Long-term monitoring shows that, with the current radar systems and operational calibration procedures, a stability of ±0.4 dB is achieved on Z d r. In that context, QPE algorithms based on K d p, which are considered to be immune to partial beam blocking, calibration, attenuation, etc., are preferred for operational use until improvements are made to the calibration of Z d r. To this end, a hybrid algorithm based on attenuation-corrected Z h for low rain rates and K d p for higher rain rates has been designed and tested Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]