SEMINAR SERIES and COLLOQUIA

Convective clouds like thunderstorms as an isolated entity bring strong rainfall in 30 minutes~1 hour and often occur in large groups and complexes, referred to as Mesoscale Convective Systems (MCSs). MCSs are generally much larger than each cloud and sometimes last for a long time through self-multiplication, which result in heavy rainfall in local area, and of considerable scientific interest and practical importance. When the generating mechanisms of MCSs are considered, one important source of air motions in clouds is the flow of air over hills and mountains. Around the Japanese Islands, rainfall affected by terrain occurs frequently. However, the mechanisms of the orographic precipitation have not been sufficiently clarified because time and space resolutions of operational observation have not been fine enough to investigate the MCSs. In this presentation, the generating and developing mechanisms of band-shaped MCS are discussed using data of Phased array wind profiler, X-band Doppler radar and upper air soundings of special observation campaign in Japan. It is suggested that the clouds organizing the rainband are formed by the triggering of the mountains and move to leeward side by background wind, and formed the band-shaped precipitation from the data analysis. Even low mountains with ~500 m height are capable of forming an organized precipitation under the environmental fields with very moist and convectively unstable atmosphere, and strong wind in the lower troposphere.

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