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 (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 coe‰cient between horizontal and vertical polarization signals (r hv ) and increase in di¤erential 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 r 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 r hv were higher than 0.98 in ST and ECT. The values of Z dr and r hv had wider variations in ICT. The characteristics of the vertical profiles of Z dr and r 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.Corresponding author and current a‰liation: Yukari Shusse, Hydrospheric Atmospheric Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601, Japan. E-mail: shusse@rain.hyarc.nagoya-u.ac.jp 6 2009, Meteorological Society of Japan Near the surface, su‰ciently below the 0 C level, ICT had larger Z dr and lower r hv than ECT in the region with Z hh stronger than 45 dBZ. This indicates that larger raindrops were more dominant in ICT than in ECT at the same Z hh in the intense rainfall regions. This di¤erence of dominant raindrop sizes appears to reflect the difference in precipitation growth processes between ICT and ECT.

Statistical Characteristics of Raindrop Size Distribution in the Meiyu Season Observed in Eastern China

“…Previous studies (e.g., Bringi et al 2006;Shusse et al 2009) have shown that Baiu events show stratiform and convective precipitation. In general, intense (weak) rainfall is generated by convective (stratiform) rain.…”

“…The Meiyu-Baiu front brings heavy rainfall in east China, mainly in the Yangtze-Huaihe River basin, and over the southern part of Japan. In recent years, authors have studied the characteristics of DSDs during the Baiu period in Japan (e.g., Harimaya 2003, 2005;Shusse et al 2009;Oue et al 2010); however, not much is known about the DSDs in the Meiyu season in China, mainly because of the lack of DSD measurements.…”

Reduction of Nonuniform Beam Filling Effects by Vertical Decorrelation: Theory and Simulations

“…The volume scan data were interpolated onto a 1 km × 1 km Cartesian grid (i, j, l) at three altitudes, l = 3, 2, and 1 km. The observations were performed in June 2004 during a frontaltype rain event with embedded and isolated convection (Shusse et al 2009). …”

Raindrop size distribution parameters estimated from polarimetric radar variables in convective cells around Okinawa Island during the Baiu period

“…In the humid environment typical of the rainy season in East Asia (called the Baiu season in Japan, Changma in Korea, and Meiyu in China), convective cells with low echo-top heights of approximately 0°C altitude are commonly observed (Zhang et al, 2006;Shusse et al, 2009). Shinoda et al (2007) reported that convective cells with low echotop (30 dBZ) heights less than 1 km above the environmental 0°C altitude accounted for over 70% of convective cells in East Asia during the Baiu period.…”