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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]

An algorithm for the detection of horizontal wind shear at low levels was developed. The algorithm makes use of data collected by all radars from the Application Radar à la Météorologie Infra-Synoptique (ARAMIS) operational network, in order to build a complete mosaic of wind shear over metropolitan France. The product provides an estimation of the maximum horizontal wind shear detected in the low levels, between 0 and 2 km AGL. Examination of the wind shear mosaic for different cases shows that the product is able to retrieve small-scale wind shear signatures that can be linked to either convergence lines ahead of convective cells, which are indicative of gust fronts, or strong convergence areas inside intense cells. A statistical evaluation of the wind shear mosaic was performed, by comparing horizontal wind shear observed inside the area defined by convective objects with wind gusts recorded along their trajectory by weather stations. A link between those different observations was clearly established. Therefore, the use of wind shear for wind gust prediction was tested in combination with other parameters: an estimation of the energetic potential of density currents, the cell surface with reflectivity over 51 dB Z, relative helicity, and cell propagation speed. Different wind gust warning rules were tested on 468 convection nowcasting objects (CONOs). The results clearly highlighted the benefits of using wind shear for wind gust estimation, and also demonstrated the improvement in forecasting skill when combining different parameters. The wind shear mosaic will be produced operationally before the end of 2013 and will be used to improve wind gust warnings provided to end users. [ABSTRACT FROM AUTHOR]

In 2012 the Météo France metropolitan operational radar network consists of 24 radars operating at C and S bands. In addition, a network of four X-band gap-filler radars is being deployed in the French Alps. The network combines polarimetric and nonpolarimetric radars. Consequently, the operational radar rainfall algorithm has been adapted to process both polarimetric and nonpolarimetric data. The polarimetric processing chain is available in two versions. In the first version, now operational, polarimetry is only used to correct for attenuation and filter out clear-air echoes. In the second version there is a more extensive use of polarimetry. In particular, the specific differential phase Kdp is used to estimate rainfall rate in intense rain. The performance of the three versions of radar rainfall algorithms (conventional, polarimetric V1, and polarimetric V2) at different frequency bands (S, C, and X) is evaluated by processing radar data of significant events offline and comparing hourly radar rainfall accumulations with hourly rain gauge data. The results clearly show a superior performance of the polarimetric products with respect to the nonpolarimetric ones at all frequency bands, but particularly at higher frequency. The second version of the polarimetric product, which makes a broader use of polarimetry, provides the best overall results. [ABSTRACT FROM AUTHOR]

Summary: Two so-called “integrated” polarimetric rate estimation techniques, ZPHI () and ZZDR (), are evaluated using 12 episodes of the year 2005 observed by the French C-band operational Trappes radar, located near Paris. The term “integrated” means that the concentration parameter of the drop size distribution is assumed to be constant over some area and the algorithms retrieve it using the polarimetric variables in that area. The evaluation is carried out in ideal conditions (no partial beam blocking, no ground-clutter contamination, no bright band contamination, a posteriori calibration of the radar variables Z H and Z DR) using hourly rain gauges located at distances less than 60km from the radar. Also included in the comparison, for the sake of benchmarking, is a conventional Z =282R 1.66 estimator, with and without attenuation correction and with and without adjustment by rain gauges as currently done operationally at Météo France. Under those ideal conditions, the two polarimetric algorithms, which rely solely on radar data, appear to perform as well if not better, pending on the measurements conditions (attenuation, rain rates, …), than the conventional algorithms, even when the latter take into account rain gauges through the adjustment scheme. ZZDR with attenuation correction is the best estimator for hourly rain gauge accumulations lower than 5mmh−1 and ZPHI is the best one above that threshold. A perturbation analysis has been conducted to assess the sensitivity of the various estimators with respect to biases on Z H and Z DR, taking into account the typical accuracy and stability that can be reasonably achieved with modern operational radars these days (1dB on Z H and 0.2dB on Z DR). A +1dB positive bias on ZH (radar too hot) results in a +14% overestimation of the rain rate with the conventional estimator used in this study (Z=282R1.66), a -19% underestimation with ZPHI and a +23% overestimation with ZZDR. Additionally, a +0.2dB positive bias on ZDR results in a typical rain rate under- estimation of 15% by ZZDR. [Copyright &y& Elsevier]

The differential phase (ΦDP) measured by polarimetric radars is recognized to be a very good indicator of the path integrated by rain. Moreover, if a linear relationship is assumed between the specific differential phase (KDP) and the specific attenuation (AH) and specific differential attenuation (ADP), then attenuation can easily be corrected. The coefficients of proportionality, γH and γDP, are, however, known to be dependent in rain upon drop temperature, drop shapes, drop size distribution, and the presence of large drops causing Mie scattering. In this paper, the authors extensively apply a physically based method, often referred to as the “Smyth and Illingworth constraint,” which uses the constraint that the value of the differential reflectivity ZDR on the far side of the storm should be low to retrieve the γDP coefficient. More than 30 convective episodes observed by the French operational C-band polarimetric Trappes radar during two summers (2005 and 2006) are used to document the variability of γDP with respect to the intrinsic three-dimensional characteristics of the attenuating cells. The Smyth and Illingworth constraint could be applied to only 20% of all attenuated rays of the 2-yr dataset so it cannot be considered the unique solution for attenuation correction in an operational setting but is useful for characterizing the properties of the strongly attenuating cells. The range of variation of γDP is shown to be extremely large, with minimal, maximal, and mean values being, respectively, equal to 0.01, 0.11, and 0.025 dB °-1. Coefficient γDP appears to be almost linearly correlated with the horizontal reflectivity (ZH), differential reflectivity (ZDR), and specific differential phase (KDP) and correlation coefficient (ρHV) of the attenuating cells. The temperature effect is negligible with respect to that of the microphysical properties of the attenuating cells. Unusually large values of γDP, above 0.06 dB °-1, often referred to as “hot spots,” are reported for 15%—a nonnegligible figure—of the rays presenting a significant total differential phase shift (ΔφDP > 30°). The corresponding strongly attenuating cells are shown to have extremely high ZDR (above 4 dB) and ZH (above 55 dBZ), very low ρHV (below 0.94), and high KDP (above 4° km-1). Analysis of 4 yr of observed raindrop spectra does not reproduce such low values of ρHV, suggesting that (wet) ice is likely to be present in the precipitation medium and responsible for the attenuation and high phase shifts. Furthermore, if melting ice is responsible for the high phase shifts, this suggests that KDP may not be uniquely related to rainfall rate but can result from the presence of wet ice. This hypothesis is supported by the analysis of the vertical profiles of horizontal reflectivity and the values of conventional probability of hail indexes. [ABSTRACT FROM AUTHOR]

The recent deployment of an innovative triple pulse rise time (PRT) scheme within the French operational radar network allows for the simultaneous collection of reflectivity and radial velocity measurements up to a range of 250 km with no ambiguity. This achievement brings new perspectives in terms of operational exploitation of Doppler measurements including the capability to consistently perform multiple-Doppler wind synthesis in a fully operational framework. Using real and simulated Doppler observations, the authors show that the 3D wind fields retrieved in that framework can definitely be relied upon to achieve a consistent and detailed mapping of the airflow structure in various precipitation regimes despite radar baselines averaging ∼180 km and very limited scanning strategies. This achievement could be easily transposed to other operational networks and represents a remarkable opportunity to add further value to operational Doppler velocity measurements. [ABSTRACT FROM AUTHOR]

Rain path attenuation correction is a challenging task for quantitative use of weather radar measurements at frequencies higher than S band. The proportionality relationship between specific attenuation αhh (specific differential attenuation αdp) and specific differential phase Kdp is the basis for simple path-integrated attenuation correction using differential phase Φdp. However, the coefficients of proportionality are known to be dependent upon temperature, on the one hand, and shape and raindrop size distribution, on the other hand. To solve this problem, a Bayesian classification scheme is proposed to empirically find the prevailing rain regime and adapt the Φdp-based method. The proposed approach herein is compared with other polarimetric techniques currently available in the literature. Several episodes observed in the Paris, France, area by the C-band dual-polarized weather radar operating in Trappes (France) are analyzed and results are discussed. [ABSTRACT FROM AUTHOR]

A fuzzy logic algorithm has been developed for the purpose of segregating precipitating from nonprecipitating echoes using polarimetric radar observations at C band. Adequate polarimetric descriptions for each type of scatterer are required for the algorithm to be effective. An observations-based approach is presented in this study to derive membership functions and objectively weight them so that they apply directly to conditions experienced at the radar site and to the radar wavelength. Three case studies are examined and show that the algorithm successfully removes nonprecipitating echoes from rainfall accumulation maps. [ABSTRACT FROM AUTHOR]

A polarimetric method is devised to correct for attenuation effects at C band on reflectivity ZH and differential reflectivity ZDR measurements. An operational cross-correlation analysis is used to derive advection vectors and to displace echoes over a 5-min time step. These advected echoes are then compared with observations valid at the same time. The method assumes that the mean change in the intrinsic ZH and ZDR over a 5-min period when considering 1–2 h of observations over the entire radar umbrella is approximately zero. Correction coefficients are retrieved through the minimization of a cost function that links observed decreases in ZH and ZDR due to attenuation effects with increases in differential phase shift (ΦDP). The retrieved coefficients are consistent with published values for the typical ranges of temperatures and drop sizes encountered at midlatitudes, even when Mie scattering effects are present. Measurements of ZH and ZDR corrected using retrieved coefficients are compared with raw measurements and to measurements adjusted by mean coefficients found in the literature. The empirical retrieval method shows improvement over using mean correction coefficients based on comparisons of ZH from neighboring, unattenuated radars, disdrometer measurements, and analysis of ZH and ZDR as a function of ΦDP. [ABSTRACT FROM AUTHOR]

The French operational radar network is being upgraded and expanded from 2002 to 2006 by Meteo-France in partnership with the French Ministry of the Environment. A detailed examination of the quality of the raw polarimetric variables is reported here. The analysis procedures determine the precision of the measurements and quantify errors resulting from miscalibration, near-radome interference, and noise effects. Correction methods to remove biases resulting from effective noise powers in the horizontal and vertical channels, radar miscalibration, and the system offset in differential propagation phase measurements are presented and evaluated. Filtering methods were also required in order to remove azimuthal dependencies discovered with fields of differential reflectivity and differential propagation phase. The developed data quality analysis procedures may be useful to the agencies that are in the process of upgrading their radar networks with dual-polarization capabilities. [ABSTRACT FROM AUTHOR]

Presents information on a study which adapted the Multiple Analytical Doppler (MANDOP) analysis to Doppler radar observations over complex orography. Formulation of the MANDOP method; Presentation of the simulation; Formulations of the boundary condition; Application to real data.

Presents a study which described a method based on a VAD analysis that provides an estimate of the wind profile directly from the raw radial velocities. Description of the classical VAD analysis; Procedure implemented for the proposed method; Operational application of the algorithm.

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]

This paper presents an analysis of a hail event that occurred 27 May 2012 over Brignoles, located in southeastern France. The event was observed by an X-band polarimetric radar located in Mont Maurel, 75 km northeast of the hailstorm. Lightning data from the French national network (owned and operated by Météorage) are also used in the study. The analysis highlights that the lightning and radar data provide complementary information that may allow a better microphysical interpretation of the hailstorm and potentially increase the probability of its detection. [ABSTRACT FROM AUTHOR]

The influence of ground clutter contamination on the estimation of polarimetric radar parameters, horizontal reflectivity (Zh), differential reflectivity (Zdr), correlation coefficient (ρhν), and differential propagation phase (φdp) was examined. This study aims to derive the critical level of ground clutter contamination for Zh, Zdr, ρhν, and φdp at which ground clutter influence exceeds predefined precision thresholds. Reference data with minimal ground clutter contamination consist of eight precipitation fields measured during three rain events characterized by stratiform and convective precipitation. Data were collected at an elevation angle of 0.8° by the Météo-France operational, polarimetric Doppler C-band weather radar located in Trappes, France, ∼30 km southwest of Paris. Nine different ground clutter signatures, ranging from point targets to more complex signatures typical for mountain ranges or urban obstacles, were added to the precipitation fields. This is done at the level of raw in-phase and quadrature component data in the two polarimetric channels. For each ground clutter signature, 30 simulations were conducted in which the mean reflectivity of ground clutter within the resolution volume varied between being 30 dB higher to 30 dB lower than the mean reflectivity of precipitation. Differences in Zh, Zdr, ρν, and φdp between simulation and reference were shown as a function of ratio between ground clutter and precipitation intensities. As a result of this study, horizontal reflectivity showed the lowest sensitivity to ground clutter contamination. Furthermore, a precision of 1.7 dBZ in Zh is achieved on average when the precipitation and ground clutter intensities are equal. Requiring a precision of 0.2 dB in Zdr and 3° in φdp, the reflectivity of precipitation needs to be on average ∼5.5 and ∼6 dB, respectively, higher compared to the reflectivity of ground clutter. The analysis also indicates that the highest sensitivity to the nine clutter signatures was derived for ρhν. To meet a predefined precision threshold of 0.02, reflectivity of precipitation needs to be ∼13.5 dB higher than the reflectivity of ground clutter. [ABSTRACT FROM AUTHOR]

A new fuzzy logic hydrometeor classification algorithm is proposed that takes into account data-based membership functions, measurement conditions, and three-dimensional temperature information provided by a high-resolution nonhydrostatic numerical weather prediction model [the Application of Research to Operations at Mesoscale model (AROME)]. The formulation of the algorithm is unique for X-, C-, and S-band radars and employs wavelength-adapted bivariate membership functions for ( ZH, ZDR), ( ZH, KDP), and ( ZH, ρHV) that were established by using real data collected by the French polarimetric radars and T-matrix simulations. The distortion of membership functions caused by deteriorating measurement conditions (e.g., precipitation-induced attenuation, signal-to-clutter ratio, signal-to-noise ratio, partial beam blocking, and distance) is documented empirically and subsequently parameterized in the algorithm. The result is an increase in the amount of overlapping between the membership functions of the different hydrometeor types. The relative difference between the probability function values of the first and second choice of the hydrometeor classification algorithm is analyzed as a measure of the quality of identification. Semiobjective scores are calculated using an expert-built validation dataset to assess the respective improvements brought by using 'richer' temperature information and by using more realistic membership functions. These scores show a significant improvement in the detection of wet snow. [ABSTRACT FROM AUTHOR]

The effect of wet radome attenuation is estimated on a French operational X-band weather radar deployed in the Maritime Alps of southeastern France. As the radar is deployed in a remote location, the reflectivity factor in the immediate vicinity of the radar is used as a proxy for rain rate at the radar and by extension, to the radome wetting. By means of intercomparison with a neighboring radar that lacks a radome, a wet radome correction is deduced. The correction is reasonably consistent with theoretical expectations and with other evaluations done, for example, via disdrometer. The improvement is evaluated by comparison to a Micro Rain Radar located under the point of comparison, and the impact on quantitative precipitation estimation (QPE) retrievals is positive. The intercomparison of such observations permits a routine means of monitoring radome attenuation. [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]

A method for the daily monitoring of the differential reflectivity bias for polarimetric weather radars is presented. Sun signals detected in polar volume data produced during operational scanning of the radar are used. This method is an extension of that for monitoring the weather radar antenna pointing at low elevations and the radar receiving chain using the sun. This “online” method is ideally suited for routine application in networks of operational radars. The online sun monitoring can be used to check the agreement between horizontal and vertical polarization lobes of the radar antenna, which is a prerequisite for high-quality polarimetric measurements. By performing both online sun monitoring and rain calibration at vertical incidence, the differential receiver bias and differential transmitter bias can be disentangled. Results from the polarimetric radars in Trappes (France) and Bornholm (Denmark), demonstrating the importance of regular monitoring of the differential reflectivity bias, are discussed. It is recommended that the online sun-monitoring method, preferably in combination with rain calibration, is routinely performed on all polarimetric weather radars because accurate calibration is a prerequisite for most polarimetric algorithms. [ABSTRACT FROM AUTHOR]

Radar reflectivity (Zh), differential reflectivity (Zdr), and specific differential phase (Kdp) measured from the operational, polarimetric weather radar located in Trappes, France, were used to examine the effects of radar beam shielding on rainfall estimation. The objective of this study is to investigate the degree of immunity of Kdp-based rainfall estimates to beam shielding for C-band radar data during four typical rain events encountered in Europe. The rain events include two cold frontal rainbands with average rainfall rates of 7 and 17 mm h-1, respectively, and two summertime convective rain events with average rainfall rates of 11 and 22 mm h-1. The large effects of beam shielding on rainfall accumulation were observed for algorithms using Zh and Zdr with differences of up to ∼2 dB (40%) compared to a Kdp-based algorithm over a power loss range of 0–8 dB. This analysis reveals that Zdr and Kdp are not affected by partial beam shielding. Standard reflectivity corrections based on the degree of beam shielding would have overestimated rainfall rates by up to 1.5 dB for less than 40% beam shielding and up to 3 dB for beam shielding less than 75%. The investigation also examined the sensitivity of beam shielding effects on rainfall rate estimation to (i) axis–ratio parameterization and drop size distribution, (ii) methods used to smooth profiles of differential propagation phase (φdp) and estimate Kdp, and (iii) event-to-event variability. Although rainfall estimates were sensitive to drop size distribution and axis–ratio parameterization, differences between Zh- and Kdp-based rainfall rates increased independently from those parameters with amount of shielding. Different approaches to smoothing φdp profiles and estimating Kdp were examined and showed little impact on results. [ABSTRACT FROM AUTHOR]