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.

During the rainy season over the East China Sea, convective rainfalls often show melting layer (ML) characteristics in polarimetric radar variables. In this research, the appearance ratio of the ML (the ratio of rainfall area accompanied by polarimetric ML signatures) and the variation in height of the level of the ML signature maximum (MLSM level; defined by the level of the r hv minimum in the ML) in a convective rainfall region in a rainfall system over the East China Sea observed on 2 June 2006 were studied using C-band polarimetric radar (COBRA). For this analysis, a method of rainfall type classification that evaluates the presence of an ML in addition to providing conventional convective-stratiform classification using rangeheight indicator (RHI) observation data was developed. This rainfall type classification includes two steps: conventional convective-stratiform separation using the horizontal distribution of Z h at 2-km altitude, and ML detection using the vertical profile of r hv at each horizontal grid point. Using a combination of these two classifications, the following four rainfall types were identified: 1) convective rainfall with an ML, 2) convective rainfall with no ML, 3) stratiform rainfall with an ML, and 4) stratiform rainfall with no ML. An ML was detected in 53.9% of the convective region in the rainfall system. Using the same definition, an ML was detected in 83.1% of the stratiform region. The ML in the convective region showed a marked decrease in r hv coincident with an increase in Z DR around the ambient 08C level, as did that in the stratiform region. Melting aggregated snow was the likely cause of the ML signature in the convective region. The average height of the MLSM level in the convective region was 4.64 km, which is 0.46 km higher than that in the stratiform region (4.18 km) and 0.27 km higher than the ambient 08C level (4.37 km).

[1] Polarimetric radar variables and ground-based raindrop size distributions (DSDs) of two convective cells in a Baiu frontal rainband over the Okinawa region were analyzed to clarify the precipitation particle distributions in convective cells with low echo top heights. One cell existed in the stratiform rain zone, and the other was in the convective rain zone of the rainband. Both cells had echo top (30 dBZ) heights of approximately 5.5 km above sea level, with large radar reflectivity (Z h ) greater than 50 dBZ in each core. For the cell in the stratiform rain zone, polarimetric variables indicated that small raindrops predominated; differential reflectivity (Z DR ) was smaller than 1.5 dB, and the correlation coefficient (r hv ) was greater than 0.98 with large Z h (!40 dBZ). The DSD showed high number densities of small raindrops with diameters of 1-2 mm. For the other cell, polarimetric variables indicated the presence of large raindrops; Z DR greater than 1.5 dB and r hv smaller than 0.98 predominated in large Z h (!40 dBZ). The DSD for this cell showed lower number densities of raindrops with diameters of 1-2 mm and higher number densities of raindrops exceeding 3 mm. The significance of these distributions was confirmed by the Z DR and r hv for 25 cells in the stratiform rain zone and for 28 cells in the convective rain zone. It is notable that different precipitation particle distributions in convective cells were found in the stratiform and convective rain zones of a Baiu frontal rainband with common characteristics of low echo top heights and large Z h .Citation: Oue, M., H. Uyeda, and Y. Shusse (2010), Two types of precipitation particle distribution in convective cells accompanying a Baiu frontal rainband around Okinawa Island, Japan,

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Dimension characteristics in precipitation properties of cumulonimbus clouds are basic parameters in understanding the vertical transport of water vapor in the atmosphere. In this study, the dimension characteristics and precipitation efficiency of cumulonimbus clouds observed in the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME) Huaihe River Basin Experiment (HUBEX) are studied using data from X-band Doppler radars and upper-air soundings. The maximum echo area (EAmax) of the cumulonimbus clouds ranged from 0.5 to 470 km2, and the maximum echo top (ETmax) ranged from 2 to 19 km. The total number of cells (TNC) within the cumulonimbus clouds over their lifetime was from 1 to 25. The ETmax, TNC, area time integral (ATI), and total rainfall amount (Rtot) strongly correlate with the EAmax of the cumulonimbus clouds. The cell-averaged ATI (ATIcell = ATI/TNC), maximum rainfall intensity (RImax), and cell-averaged rainfall amount (Rcell = Rtot/TNC) increase when the EAmax is smaller than 100 km2. On the other hand, they are almost constant when the EAmax is larger than 100 km2. The rain productivity of small clouds (<100 km2 in EAmax) increases not only by the increase of the TNC but also by the intensification of cells, while that of large cumulonimbus clouds (>100 km2 in EAmax) increases by the increase of the TNC rather than by the intensification of cells. In the present study, precipitation efficiency (ɛp) is defined as the ratio of the total rainfall amount (Rtot) to the total water vapor amount ingested into the cloud through the cloud base (Vtot). The ɛp was calculated for six clouds whose vertical velocity data at the cloud-base level were deduced by dual-Doppler analysis throughout their lifetime. The ɛp ranged from 0.03% to 9.31% and exhibited a strong positive correlation with the EAmax. This indicates that more than 90% of the water vapor that enters the clouds through the cloud base is consumed to moisten the atmosphere and less than 10% is converted to precipitation and returned to the ground. The cumulonimbus clouds in the region far south from the mei-yu front over the eastern Asian continent efficiently transport water vertically and humidify the upper troposphere.