We observed a meso-gamma-scale convective system in July 2007 using a 443-MHz wind profiler radar (WPR) with a radio acoustic sounding system (RASS) at the Nucl. Ogimi observatory in Okinawa, Japan. We analyzed the virtual temperature, T-v, the Brunt-Vaisala frequency squared, N-2, and three components of wind velocity profiles from the WPR-RASS data. We also employed a non-hydrostatic meso-scale (NHM) numerical model. Although the island of Okinawa was covered with a Pacific high-pressure system from 21-26 July, the atmospheric condition was convectively unstable below about 5 km. A number of convective clouds generally appeared from 11:00-18:00 in local time (i.e., Japan Standard Time; JST) with a typical horizontal scale of 10 km and temporal scale of 40-60 min. We focused on the convective system that passed over the Ogimi radar site on 23rd and 25th July. Just before rain occurred on these days, a low N-2 region extended upward to 2.0 km, and this characteristics is also commonly seen around a convective cloud in the NHM model. The cloud water content from the NHM model indicated that the cloud top height correlates with the low N-2 structure. Before the convective system was generated, N-2 decreased below an altitude of about 1 km, because air with low T-v intruded at 1-3 km, and the surface temperature increased due to solar radiation. The sea-breeze from both the east and west coasts of Okinawa collided to force the convergence below 1 km. Thus, the synergetic effects of the low static stability and convergence seemed to trigger the generation of a convective system, which eventually grew to 11 km over the radar site. (C) 2010 Elsevier Ltd. All rights reserved.
