Characteristics of Polarimetric Radar Variables in Three Types of Rainfalls in a Baiu Front Event over the East China Sea

Abstract

Characteristics of polarimetric radar variables in three rainfall types in a Baiu front event over the East China Sea observed on 1 June 2004 were studied and compared using a C-band polarimetric radar, the CRL Okinawa bistatic polarimetric radar (COBRA). The selected rainfalls are common types in the Baiu season in this area: (1) stratiform type (ST), (2) isolated convective type (ICT) and (3) embedded convective type (ECT). ST was characterized by an obvious bright band in the field of radar reflectivity (Zhh). ICT and ECT had almost the same 30-dBZ echo-top height of about 5.5 km, and their strong echo region (Zhh > 40 dBZ) did not exceed the 0°C level (4.4 km altitude) even in their mature stages.Around the 0°C level, overall decrease in correlation coefficient between horizontal and vertical polarization signals (ρhv) and increase in differential reflectivity (Zdr) were observed in ST and ECT, which indicated the presence of a layer of mixed-phase precipitation. By contrast, significant decrease in ρhv and increase in Zdr were not found in ICT. At lower levels, Zdr ranged from 0 to 1.5 dB and most of ρhv were higher than 0.98 in ST and ECT. The values of Zdr and ρhv had wider variations in ICT. The characteristics of the vertical profiles of Zdr and ρhv in ECT are consequently more similar to those in ST rather than to those in ICT, although their echo-top heights of 30 dBZ and maximum Zhh near the surface were almost equal.