Abstract
Polarimetric radar measurements and products perform as the cornerstones of modern severe weather warning and nowcast systems. Two radar quantitative precipitation estimation (QPE) frameworks, one based on a radar-gauge feedback mechanism and the other based on standard rain drop size distribution (DSD)-derived rainfall retrieval relationships, are both evaluated and investigated through an extreme severe convective rainfall event that occurred on 23 June 2015 in the mountainous region over eastern China, using the first routinely operational C-band polarimetric radar in China. Complex rainstorm characteristics, as indicated by polarimetric radar observables, are also presented to account for the severe rainfall field center located in the gap between gauge stations. Our results show that (i) the improvements of the gauge-feedback-derived radar QPE estimator can be attributed to the attenuation correction technique and dynamically adjusted Z–R relationships, but it greatly relies on the gauge measurement accuracy. (ii) A DSD-derived radar QPE estimator based on the specific differential phase (KDP) performs best among all rainfall estimators, and the interaction between the mesocyclone and the windward slope of the mountainous terrain can account for its apparent overestimation. (iii) The rainstorm is mainly dominated by small-sized and moderate-sized raindrops, with the mean volume diameter being less than 2 mm, but its KDP column (KDP > 3°·km−1) has a liquid water content that is higher than 2.4815 g·m−3, and a high raindrop concentration (Nw) with log10(Nw) exceeding 5.1 mm−1m−3. In addition, small hailstones falling and melting are also found in this event, which further aggregates Nw upon the severe rainfall center in the gap between gauge stations.
Highlights
Compared with the traditional single polarization Doppler weather radars that produce horizontal reflectivity (ZH ), radial velocity (Vr), and spectrum measurements, the polarimetric radar system can provide additional variables, including differential reflectivity (ZDR ), copolar correlation coefficient, differential propagation phase (ΦDP ), and specific differential phase (KDP ) [1], and these polarimetric radar measurements have been demonstrated to be very useful in meteorologicalRemote Sens. 2019, 11, 22; doi:10.3390/rs11010022 www.mdpi.com/journal/remotesensingRemote Sens. 2019, 11, 22 and hydrological applications
The severe rainfall event that occurred during 0800–1000 UTC, 23 June 2015 was mainly caused by a severe convective rainstorm, accompanied by a significant interaction of a mesocyclone with the northwestern mountainous terrain of Hangzhou
The vertical cross-section (VCS) structures of Vr were oriented to the gauge stations, all presenting more severe convective characteristics than that at 0829 UTC, except that orienting to DC
Summary
Compared with the traditional single polarization Doppler weather radars that produce horizontal reflectivity (ZH ), radial velocity (Vr), and spectrum measurements, the polarimetric radar system can provide additional variables, including differential reflectivity (ZDR ), copolar correlation coefficient (ρHV ), differential propagation phase (ΦDP ), and specific differential phase (KDP ) [1], and these polarimetric radar measurements have been demonstrated to be very useful in meteorologicalRemote Sens. 2019, 11, 22; doi:10.3390/rs11010022 www.mdpi.com/journal/remotesensingRemote Sens. 2019, 11, 22 and hydrological applications. All of the operational weather radars in the U.S (i.e., Next-Generation Radar—NEXRAD) and some weather radar sites in Europe have been upgraded with dual-polarization capability. In China, over 200 single-polarization weather radars have been deployed nationwide for severe weather warning and nowcast operations. Most of these radar systems deployed in eastern China are S-band, and those deployed in western China are C-band. A C-band polarimetric radar for the gap-filling of current operational S-band weather radar networks has been deployed and put into routine meteorological operation in Hangzhou, China, since 2015. The efficient and comprehensive utilization of these polarimetric radars for severe weather diagnosis, warning, and decision-making based on the derived numerical products is still a major task of the Chinese
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