Structure and mechanism of meso-scale low and heavy rainfall along the Baiu front

2004年5月21日至6月11日，我们利用多普勒雷达在宫古群岛和冲绳进行了一次密集观测，观测到了与沿沿着白鸥锋面的中尺度低压相关的暴雨。在观测过程中观测到许多不同类型的降水系统。利用雷达资料研究了降水系统的结构和过程。特别是对2003年6月7-8日在宫古地区观测到的中尺度低压和相关降水进行了详细的研究。利用CReSS（Cloud Resolving Storm Simulator）云分辨模式，对中尺度低压、白乌锋、次天气低压和降水进行了模拟试验。利用CReSS模式成功地模拟出了白乌锋面沿着副天气低压内部中尺度低压的发展过程。利用地球模拟器对这次中尺度低压进行了高分辨率模拟。结果表明，中尺度低压是白浪锋面多尺度结构的一种，积雨云对中尺度低压的发展起着重要作用。2004年7月12-13日，新泻县和福岛县发生了一次强降水过程。资料分析表明，暴雨发生在沿着白乌锋形成的一个中低压的东南部。利用CReSS模式对这次暴雨过程和白乌锋面中尺度低压进行了数值模拟试验。对模拟结果的详细分析表明，这次暴雨是在中尺度低压南侧的高湿区发展形成雨带并维持较长时间所致。

During the period from 21 May 2004 to 11 June 2004, we performed an intensive observation in the Miyako Islands and Okinawa Island using Doppler radars to observe heavy rainfall associated with a meso-scale low along the Baiu front. Many different types of precipitation systems were observed during the observation. Using the data of the radars, we investigated structures and processes of the precipitation systems. In particular, a detailed study was performed about the meso-scale low and associated precipitation observed on 7-8 June 2003 in the Miyako area. We found a characteristic wind structure with the precipitation system.Using the cloud-resolving model named CReSS (Cloud Resolving Storm Simulator), we performed a simulation experiment of the meso-scale low, the Baiu front, sub-synoptic low and associated precipitation. The development of meso-scale low within the sub-synoptic low along the Baiu front was successfully simulated by the CReSS model. Using the Earth simulator, a high -resolution simulation of the meso-scale low was performed. The result showed that the meso-scale low is one of the class of the multi-scale structure of the Baiu front and that cumulonimbus clouds are essentially important for the development of the meso-scale low.A heavy rainfall event occurred in Niigata and Fukushima prefectures on 12-13 July 2004. A data analysis indicates that the heavy rain occurred to the southeast of a meso-low formed along the Baiu front. Using the CReSS model, we performed a simulation experiment of the heavy rainfall and the Baiu frontal meso-scale low. An detailed analysis of the simulated result showed that a rainband developed within a highly humid region to the south of the meso-scale low and the maintenance for long time resulted in the heavy rainfall.