Correction of Radar Reflectivity and Differential Reflectivity for Rain Attenuation at X Band. Part II: Evaluation and Application

Abstract

In this paper, the attenuation-correction methodology presented in Part I is applied to radar measurements observed by the multiparameter radar at the X-band wavelength (MP-X) of the National Research Institute for Earth Science and Disaster Prevention (NIED), and is evaluated by comparison with scattering simulations using ground-based disdrometer data. Further, effects of attenuation on the estimation of rainfall amounts and drop size distribution parameters are also investigated. The joint variability of the corrected reflectivity and differential reflectivity show good agreement with scattering simulations. In addition, specific attenuation and differential attenuation, which are derived in the correction procedure, show good agreement with scattering simulations. In addition, a composite rainfall-rate algorithm is proposed and evaluated by comparison with eight gauges. The radar-rainfall estimates from the uncorrected (or observed) ZH produce severe underestimation, even at short ranges from the radar and for stratiform rain events. On the contrary, the reflectivity-based rainfall estimates from the attenuation-corrected ZH does not show such severe underestimation and does show better agreement with rain gauge measurements. More accurate rainfall amounts can be obtained from a simple composite algorithm based on specific differential phase KDP, with the R(ZH_cor) estimates being used for low rainfall rates (KDP ≤ 0.3° km−1 or ZH_cor ≤ 35 dBZ). This improvement in accuracy of rainfall estimation based on KDP is a result of the insensitivity of the rainfall algorithm to natural variations of drop size distributions (DSDs). The ZH, ZDR, and KDP data are also used to infer the parameters (median volume diameter D0 and normalized intercept parameter Nw) of a normalized gamma DSD. The retrieval of D0 and Nw from the corrected radar data show good agreement with those from disdrometer data in terms of the respective relative frequency histograms. The results of this study demonstrate that high-quality hydrometeorological information on rain events such as rainfall amounts and DSDs can be derived from X-band polarimetric radars.

Behavior and Structure of Convective Clouds Developing around a Mountainous Area Observed by Stereo Photogrammetry and Ka-Band and X-Band Radars: Case Study of Northern Kanto, Japan

“…For analysis of the X-band radar data, we converted the reflectivity and Doppler velocity obtained from each radar into 1 × 1 × 0.25 km of Constant Altitude PPI (CAPPI) by Cressman interpolation (Cressman 1959). For reflectivity, only the X-band radar located at Moka was used because attenuation correction was conducted using polarimetric parameters by the method of Park et al (2005). For calculation of wind vectors, the three-dimensional variational method used by Shimizu and Maesaka (2007) was applied.…”

Quantitative Precipitation Estimation and Hydrological Modeling in Japan

“…To minimize errors in rainfall estimates, JMA constantly updates data using limited Automated Meteorological Data Acquisition System (AMeDAS) gauge stations (Sugiura, 2013). The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) established an X-band polarimetric radar network (XRAIN), which uses an operational data processing system developed by the National Research Institute for Earth Science and Disaster Prevention (NIED; Maki et al, 2005;Park et al, 2005;Maesaka et al, 2011). XRAIN is composed of X-band MP (multi-parameter) radars, and has spatial and temporal resolutions of 250-m and 1-min, respectively.…”

“…The proven effectiveness of these systems in tracking typhoons instigated the deployment of the operational weather radar network in Japan. Since that time, ongoing weather radar observation research for QPE has been conducted throughout Japan, and much progress has been made in this field (Iwanami et al, 2001;Iwanami et al, 2003;Maki et al, 2005;Park et al, 2005;Maesaka et al, 2011;Kim and Maki, 2012;P.C. et al, 2013;P.C.…”

Localized Heavy Rainfall Near Zoshigaya, Tokyo, Japan on 5 August 2008 Observed by X-band Polarimetric Radar - Preliminary Analysis -

“…The application of the differential propagation phase as a powerful measure of rainfall has led to strong interest in polarimetric radar because differential phase measurement has a weaker dependence on variable drop size, rainfall attenuation, beam blockage, hail presence and errors associated with the calibration of radar hardware (e.g., Matrosov et al 1999;Chandrasekar et al 2002;Matrosov et al 2002;Anagnostou et al 2004;Maki et al 2005b;Matrosov et al 2005;Park et al 2005;Maki et al 2006). Radar that operates at relatively short wavelengths, such as X-band (3 cm wavelength) radar, is the most useful in dedicated hydrological applications because it is possible to achieve fine spatial resolution, is easy to set up in urban or mountainous areas, and is less expensive than S-and C-band wavelength radar.…”

“…The rain rate is calculated using the composite method, as proposed by Park et al (2005). This approach is based on R-KDP and R-Z relationships, where R, KDP, and Z are the rain rate, specific differential phase, and reflectivity factor, respectively.…”