Two types of precipitation particle distribution in convective cells accompanying a Baiu frontal rainband around Okinawa Island, Japan

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 (ρ_hv) was greater than 0.98 with large Z_h (≥40 dBZ). The DSD showed high number densities of small raindrops with diameters of 12 mm. For the other cell, polarimetric variables indicated the presence of large raindrops; Z _DR greater than 1.5 dB and ρ_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 ρ_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.