To understand the formation and maintenance mechanism of Mesoscale Convective Systems (MCSs) around the Meiyu/Baiu front, characteristics of Cloud Clusters (CCs) which appeared around the front over China continent and East China Sea during June and July of five years (1998-2002) were investigated by using infrared TBB data of Geostationary Meteorological Satellite (GMS).
Diurnal variation of convective activity is predominant over land during warm season in East Asia. The magnitude of the diurnal variation is known to be different over different geography like a plain, mountains, ocean, etc. However few researchers have investigated the relationship between the appearance characteristics of CC and the geography. In this study, analysis areas containing the eastern part of China and East China Sea, where CC appears frequently along the Meiyu/Baiu front, were classified into four domains: Yangtze River basin, Southeast Mountains, northern part of East China Sea, southern part of East China Sea. Characteristics of CC were investigated for each of the four domains and surrounding areas. An algorithm to detect and identify CC automatically was developed and 2044 CCs were tracked objectively. Following characteristics of CC around the Meiyu/Baiu front in the four domains were clarified.
Over land, diurnal appearance of CC having an afternoon peak was predominant in Yangtze River basin in July, and Southeast Mountains in both June and July. However, it was not predominant in Yangtze River basin in June. CCs in Southeast Mountains had shorter lifetime and smaller maximum area than those in Yangtze River basin on average. Over East China Sea, a lot of CCs appeared around 6 o’clock (local time) in the northern part in both June and July. They had longer lifetime and larger maximum area than those over land. Though CCs in the southern part were smaller and lived shorter, some of them appeared simultaneously nearby each other and developed to a huge cluster. Diurnal variation of surface temperature calculated from an objective analysis data provided by Japan Meteorological Agency was consistent with the diurnal appearance of CC in each domain. These findings would contribute for the improvement of forecasting CCs and associated heavy rainfalls.
By tracking CCs objectively, a generation area of CCs, which develop to meso-alpha low and produce heavy rainfalls, was recognized around the downstream of Yangtze river and the west pat of East China Sea. The relation between characteristics of CC in the Meiyu/Baiu front and structure of rainfall systems is discussed in comparison with Doppler radar analyses on a few intensive field experiments.