Rainfall estimation from C-band polarimetric radar in Okinawa, Japan: Comparisons with 2D-video disdrometer and 400 MHz wind profiler

This paper presents an inter-comparison of rainfall parameters (median volume diameter and rain rate) using C-band polarimetric radar, a 2D-video disdrometer and a 400 MHz profiler for the Baiu front event of 8-9 June 2005 in Okinawa, Japan. These instruments are part of the Okinawa Sub-Tropical Environment Remote Sensing Center, operated by the National Institute of Information and Communications Technology (NICT). The 2D-video disdrometer is used to derive the mean axis ratio of raindrops versus drop diameter, as well as the drop size distribution for the Baiu event. The data are then used to simulate various relations between polarimetric scattering parameters such as: specific attenuation (A(h)), and specific differential attenuation (Ad(dp)), versus specific differential phase (K-dp) which are required to correct the measured reflectivity at horizontal polarization (Z(h)), and the differential reflectivity (Z(dr)) for rain attenuation. The 2D-video disdrometer data are also used to arrive at retrieval formulas for median volume diameter (D-0) from radar Zd(dr), and rain rate from radar K-dp. The intense Baiu event of 8-9 June 2005 was composed of heavy convective rain cells embedded in large areas of stratiform rain. The inter-comparison of D-0 and rain rate (R) between instruments was conducted for 12 hours (03:00-07:00, 11:00-19:00 UTC on 8th June 2004). The C-band radar retrievals were found to be in excellent agreement with the 2D-video disdrometer for the entire period. The 400 MHz profiler retrievals of D-0 and R were in good agreement with 2D-video disdrometer during the more steady rain periods, with more scatter observed during the heavier convective rain periods. These inter-comparisons demonstrate the accuracy of C-band polarimetric radar to retrieve important rainfall parameters, as well as the accurate correction for rain attenuation using differential propagation phase.