Case study of a long-lived cloud cluster

[摘要] A mesoscale cloud cluster was observed around a cyclone from the 7th to the 9th of October in 1983. Its synoptic situation, behavior and structure were studied using the data of satellites, radars, upper air sounding and rainfall amount. The cloud cluster formed in association with a cyclone which was found in the zone of large moisture gradient. It was initiated in the warm sector of the cyclone and then it approached to the warm front. The area of upward motion and convective instability, which were favorable for the development of convection, were localized in the limited region in the warm sector of the cyclone and the cluster was observed near this region. In spite of the east-north-eastward movement of the cyclone, the cloud cluster stayed in the south of central part of Japan for more than 6 hours.Satellite IR data show that the evolution process of the cloud cluster was divided into two stages. In stage I the minimum equivalent blackbody brightness temperature (TBB) of this cloud cluster was less than -70°C. Its shape was oval. The maximum radii of cloud areas whose TBB were below -40°C and -60°C were about 170km and 120km, respectively. In this stage the cloud cluster existed mainly in the warm sector.In stage II the area of TBB lower than -60°C remained small. In contrast the area of TBB lower than -40°C increased again and it was elongated northeastward. Its width and length were 100km and several-hundred kilometers, respectively. The cloud cluster consisted of the southwestern convective clouds, which were aligned northeastward, and the northeastern layer clouds which were composed of upper-level generating cells and middle-level clouds. In this stage the cloud cluster existed across the warm frontal region. Its northeastern part existed in the region which is characterized by warm moist and stable air above the frontal layer and cold moist air under the frontal layer. There was localized area of convective instability above the frontal layer and this area would have been related to the formation of upper-level generating cells.

[学科分类] 大气科学