Abstract
A climatological analysis of cyclogenesis over east Asia and the adjacent northwest Pacific for the period 1958–87 based on the Beijing Meteorological Center' historical surface maps is presented. The most active cyclogenetic areas were: 1) the lee sides of the Altai-Sayan, Stanovoi, and Great Xinganling mountains, and 2) the East China Sea and the Sea of Japan. The former was related to lee cyclogenesis and the latter to coastal cyclogenesis. After zonal average, the primary zone of cyclogenesis emerged between 45° and 50°N, constituted mainly by the Altai-Sayan lee cyclogenesis. The Altai-Sayan lee cyclogenesis occurred in all seasons, with peak frequencies from April to May and from August to September. The secondary zone of cyclogenesis, located at 30°–35°N with half the frequency of the primary zone, was a result of East China Sea cyclogenesis. The coastal cyclogenesis occurred only in the cold season and disappeared in summer and early autumn. The total cyclogenetic events over east Asia reached a minimum in January. By contrast, cyclogenesis is still quite active over North America in January. The trend of east Asia cyclogenesis showed a decline from 1958–77, which was coincident with the finding of Whittaker and Horn in North America. After 1977, no such decline was found.
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