Improving Polarimetric C-Band Radar Rainfall Estimation with Two-Dimensional Video Disdrometer Observations in Eastern China

Abstract

In this study, the capability of using a C-band polarimetric Doppler radar and a two-dimensional video disdrometer (2DVD) to estimate monsoon-influenced summer rainfall during the Observation, Prediction and Analysis of Severe Convection of China (OPACC) field campaign in 2014 and 2015 in eastern China is investigated. Three different rainfall R estimators, for reflectivity at horizontal polarization [R(Zh)], for reflectivity at horizontal polarization and differential reflectivity factor [R(Zh, Zdr)], and for specific differential phase [R(KDP)], are derived from 2-yr 2DVD observations of summer precipitation systems. The radar-estimated rainfall is compared to gauge observations from eight rainfall episodes. Results show that the two polarimetric estimators, R(Zh, Zdr) and R(KDP), perform better than the traditional Zh–R relation [i.e., R(Zh)]. The KDP-based estimator [i.e., R(KDP)] produces the best rainfall accumulations. The radar rainfall estimators perform differently across the three organized convective systems (mei-yu rainband, typhoon rainband, and squall line). Estimator R(Zh) overestimates rainfall in the mei-yu rainband and squall line, and R(Zh, Zdr) mitigates the overestimation in the mei-yu rainband but has a large bias in the squall line. QPE from R(KDP) is the most accurate among the three estimators, but it possesses a relatively large bias for the squall line compared to the mei-yu case. The high variability of drop size distribution (DSD) related to the precipitation microphysics in different types of rain is largely responsible for the case-dependent QPE performance using any single radar rainfall estimator. The squall line has a distinct ice-phase process with a large mean size of raindrops, while the mei-yu rainband and typhoon rainband are composed of smaller raindrops. Based on the statistical QPE error in the ZH–ZDR space, a new composite rainfall estimator is constructed by combining R(Zh), R(Zh, Zdr), and R(KDP) and is proven to outperform any single rainfall estimator.

Microphysical Characteristics of Three Convective Events with Intense Rainfall Observed by Polarimetric Radar and Disdrometer in Eastern China

“…Flash floods associated with these extreme precipitation events occur frequently in eastern China, causing severe damage to properties and loss of lives. To improve variables are the same as in Chen et al [22]. Firstly the system biases for the radar reflectivity (Z H ) and differential reflectivity (Z DR ) are calibrated using a metal sphere experiment and the vertically pointing data in light rain, respectively.…”

“…After eliminating the non-meteorological echoes, an enhanced linear programming method [23] is used for the recalculation of the specific differential phase (K DP ). Then the attenuation of Z H (Z DR ) are corrected based on the linear relation between the specific horizontal attenuation A H (the specific differential attenuation A DP ) and K DP [22]. After QC, the radar data in each volume coverage pattern (VCP), consisting 14-elevation Plan Position Indicator (PPI) scans, are interpolated onto constant altitude PPI (CAPPI) in a Cartesian grid using the NCAR REORDER software package with 1.0 km horizontal and 0.5 km vertical grid spacing starting from 0.5 km above ground level (AGL).…”

Analysis of Dual-Polarimetric Radar Variables and Quantitative Precipitation Estimators for Landfall Typhoons and Squall Lines Based on Disdrometer Data in Southern China

“…However, R3(Z H , Z DP ) is underestimated, whereas the other three are overestimated. The performance of R1(Z H ) is the worst because only one variable Z H is used and Z H fluctuated greatly with the DSDs [36,46]. The performance of R2(K DP ) is better than that of R1(Z H ), which can be attributed to the fact that the exponent of K DP is closer to 1 than that of Z H .…”

“…Linlin Wu [26] calculated several rainfall estimators for C-band radar based on 1D laser disdrometer data, R(Z H ), R(Z H , Z DR ), R(K DP ), and R(K DP , Z DR ), in the Jiang-Huai region of China. Gang Chen et al [36] proposed rainfall estimators R(Z H ), R(Z H , Z DR ), and R(K DP ) for a C-band dual-pol radar based on 2D video disdrometer (2DVD) data in eastern China.…”

Current Status and Future Challenges of Weather Radar Polarimetry: Bridging the Gap between Radar Meteorology/Hydrology/Engineering and Numerical Weather Prediction

“…The use of PRD can provide vital real-time information to forecasters, thus helping to improve severe weather detection and warnings, but many of the methods are oftentimes subjective and empirical, and have limitations in realizing the full potential of PRD. In QPE, deterministic power-law relations are used for rain estimation from PRD Chen et al, 2017), which may not be optimal. Also, uncertainties of radar-derived products have not been accurately quantified and provided together with the products.…”