Long‐term monitoring of French polarimetric radar data quality and evaluation of several polarimetric quantitative precipitation estimators in ideal conditions for operational implementation at C‐band

Abstract

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 dp , (ii) an algorithm based on reflectivity (Z h ) and differential reflectivity (Z dr ), and (iii) algorithms based on specific differential phase (K dp ).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 dr , 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 dr . In that context, QPE algorithms based on K dp , 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 dr . To this end, a hybrid algorithm based on attenuationcorrected Z h for low rain rates and K dp for higher rain rates has been designed and tested Copyright c 2012 Royal Meteorological Society Key Words: polarimetry; polarimetric processing; radar calibration; radar-raingauge comparisons

The New French Operational Polarimetric Radar Rainfall Rate Product

“…It enables identification of the scatterers (Park et al 2009), attenuation correction (Gu et al 2011), and real-time retrieval of the DSD parameters (Brandes et al 2004). Numerous polarimetric QPE algorithms have been proposed at S, C, and X band (see Ryzhkov et al 2005;Bringi et al 2011;Tabary et al 2011;Figueras i Ventura et al 2012a).…”

“…A hybrid reflectivity-rainfall (Z-R) and specific differential phase (K dp )-R algorithm was considered the best choice. The research is described in detail in Figueras i Ventura et al (2012a). This algorithm is implemented in the second version of the operational polarimetric radar rainfall product.…”

“…The installation was followed by a long period of research and development [see Figueras i Ventura et al (2012a) for an overview], which finally resulted in a first version of a polarimetric preprocessing chain introduced into operations in February 2012. This first version basically corrects for precipitationinduced attenuation the radar reflectivity Z h using the differential phase f dp .…”

Estimation of Raindrop Size Distribution and Rainfall Rate from Polarimetric Radar Measurements at Attenuating Frequency Based on the Self-Consistency Principle

“…A typical solution for S-band is a combination of an R(K DP ) for high rainfall rates and an R(Z H , Z DR ) relation for lower rainfall rates (e.g., Ryzhkov et al 2005;Cifelli et al 2011). At C-and X-band, where attenuation is more significant than at S-band (Smyth and Illingworth 1998), R(K DP ) is applied for a larger range of rain intensities and an R(Z H ) relation is usually used for lighter rain with polarimetrically corrected reflectivity (e.g., Park et al 2005a;Figueras i Ventura et al 2012;Vulpiani et al 2012;Yamauchi et al 2012). More recently, Ryzhkov et al (2014) showed that the rainfall rate estimated from the specific attenuation A H is the least sensitive to DSD variations and has some advantages compared with rainfall rates estimated from Z H or Z DR and/or K DP .…”

Coupling X-band dual-polarized mini-radars and hydro-meteorological forecast models: the HYDRORAD project

“…Meteorological services across Europe are using networks of weather surveillance radars, which can advance precipitation monitoring with direct implications on the improvement of real-time forecasting of river floods and flash floods in ungauged basins (Ventura et al, 2012). Precipitation, though, may originate from varying meteorological systems, ranging from cold frontal systems to thunderstorms, and maritime systems, where rainfall estimates based on these classical single polarization radar observations have quantitative limitations.…”