Operational C-Band Dual-Polarization Radar QPE for the Subtropical Complex Terrain of Taiwan

Abstract

Complex terrain poses significant challenges to the radar based quantitative precipitation estimation (QPE) because of blockages to the lower tilts of radar observations. The blockages often force the use of higher tilts data to estimate precipitation at the ground and result in errors due to vertical variations of the radar variables. To obtain accurate radar QPEs in the subtropical complex terrain of Taiwan, a vertically corrected composite algorithm (VCCA) was developed for two C-band polarimetric radars. The new algorithm corrects higher tilt radar variables with the vertical profile of reflectivity (VPR) or vertical profile of specific differential phase (VPSDP) and estimates rainfall rate at the ground through an automated combination ofR-ZandR-KDPrelations. The VCCA was assessed with three precipitation cases of different regimes including typhoon, mei-yu, and summer stratiform precipitation events. The results showed that a combination ofR-ZandR-KDPrelations provided more accurate QPEs than each alone becauseR-Zprovides better rainfall estimates for light rains andR-KDPrelation is more suitable for heavy rains. The vertical profile corrections for reflectivity and specific differential phase significantly reduced radar QPE errors caused by inadequate sampling of the orographic enhancement of precipitation near the ground.

A Prototype Quantitative Precipitation Estimation Algorithm for Operational S-Band Polarimetric Radar Utilizing Specific Attenuation and Specific Differential Phase. Part I: Algorithm Description

“…where the coefficients g and L depend on the radar wavelength, temperature, and polarization. Applications of the R(A) relations for C-band and X-band polarimetric radars were also investigated by Wang et al (2014), Giangrande et al (2014), Boodoo et al (2015), and Diederich et al (2015). Although the R(A) relation is less sensitive to the DSD variations than the R(Z), R(Z, Z DR ), and R(K DP ) relations, the impact of the DSD variability on the estimate of A can still be significant.…”

“…Generally, at S band, the R(K DP ) relation is used in a mixture of rain and hail and the R(Z, Z DR ) relation in pure rain (Giangrande and Ryzhkov 2008;Cifelli et al 2011;Chen et al 2017). The R(K DP ) relation is utilized in a wide range of rain intensities at C and X bands complemented by R(Z) in light rain (e.g., Park et al 2005;Figueras i Ventura et al 2012;Vulpiani et al 2012;Yoshikawa et al 2012;Chen and Chandrasekar 2015;Wang et al 2016;Cifelli et al 2018).…”

“…A similar consideration is valid with respect to the temperature provided that the temperature dependence of a is taken into account and the temperature does not vary much along the propagation path in rain. This means that, to the first approximation, it is possible to use a single universal R(A) relation in a given microwave frequency band and ignore the dependencies of the factors g and a on the radar wavelength and temperature (Ryzhkov et al 2014;Wang et al 2014;Diederich et al 2015). A single R(A) relation was proposed for the operational network of the S-band WSR-88D radars in the United States (Ryzhkov et al 2014):…”

“…The temperature impact on the performance of C-band R(A) was investigated by Wang et al (2014), and it was found that 188C temperature variation may cause less than 15% bias on the obtained rainfall rate. It was also found that indistinguishable bias is caused by the temperature variation of 58C if a single R(A) relation is used at X band (Diederich et al 2015).…”

A Case Study for the Application of an Operational Two-Dimensional Real-Time Flooding Forecasting System and Smart Water Level Gauges on Roads in Tainan City, Taiwan

“…The QPESUMS was based on six Doppler radars in Taiwan to estimate the precipitation and other hydrologic parameters, and it has been used to monitor severe weather since 2003. The weather information is updated every 10 min including 1.3-km resolution rainfall intensities covering all Taiwan land area [21,22]. The grid resolution of rainfall data was 1.3 km × 1.3 km, while the interval was 10 min.…”