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

抄録

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 (Z_hh). ICT and ECT had almost the same 30-dBZ echo-top height of about 5.5 km, and their strong echo region (Z_hh > 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 (ρ_hv) and increase in differential reflectivity (Z_dr) were observed in ST and ECT, which indicated the presence of a layer of mixed-phase precipitation. By contrast, significant decrease in ρ_hv and increase in Z_dr were not found in ICT. At lower levels, Z_dr ranged from 0 to 1.5 dB and most of ρ_hv were higher than 0.98 in ST and ECT. The values of Z_dr and ρ_hv had wider variations in ICT. The characteristics of the vertical profiles of Z_dr and ρ_hv 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 Z_hh near the surface were almost equal.