Improvement of rainfall estimation algorithm using the latest C-band polarimetric radar

摘要

Improvement of quantitative precipitation estimation (QPE) is one of the primary benefits provided by polarization radars. Ministry of Land, Infrastructure and Transportation Japan (MLIT) put Shakadake operational C band polarimetric radar to practical use in 1992. However, large improvement had not been realized because of its initial technical stage. Under these circumstances, this study propose a new algorithm on QPE using the latest C band polarimetric radar for promoting replacement of Japanese operational radars into operational polarimetric Doppler radars. The latest polarimetric radar we used is the COBRA (CRL Okinawa Bistatic polarimetric Radar) developed by National Institute of Information and communications Technology (NICT) in Okinawa, Japan. The radar observation is synchronized with DSD (Drop size Distribution) observations. As results, this study shows Zhh> Zdr and KDP observed by the polarization well fit to Zhh, Zdr and KDP nonparametrically computed from observed DSD, respectively. Also, this study shows "Radar observed Zdr-Dm" relation is consistent with observed DSD. Here, Dm is the mass-weighted mean diameter. Based on these basic investigations, an algorithm for estimating rainfall intensity is developed with two points: ①Mass-weighted diameter Dm was introduced into rainfall estimators R(ZHH) and R(Kdp), as R(ZHH, Dm) and R(KDp, Dm); ②Dm was used also in the selection of R(Zhh, Dm) or R(Kdp, Dm). As a result, it was found that the estimate accuracy was improved well.