On the Mesoscale and Medium-scale Structure of a Cold Front and the Relevant Vertical Circulation

Abstract

 Msoscale and medium-scale structures of the Baiu front are studied for the case of July 8, 1969, on which special observations including aerial and ground-base mesoscale upper air soundings were being operated by the Severe Rainstorms Research Project. Within the region of a synoptic scale cyclone generated on the Baiu frontal zones, a medium-scale structure is found which is further decomposed into mesoscale rain bands in the vicinity of the cold front part of that cyclone. A finer structure is also depicted in a low-level jet stream which often appears in the Baiu season particularly at a time of heavy rainfall.
 Based on wind, temperature and relative humidity field analyses, some dynamical considerations and numerical experiments are made on the generation of the low-level jet stream and relevant vertical circulation.