Climatology of deep cyclones over Asia and the Northwest Pacific

Summary

A frequency analysis of deep cyclones with central pressure less than or equal to 990 hPa over Asia and the Northwest Pacific in the period 1958–1989 is presented. The most active areas of deep cyclones are: 1) Western Siberia, east of the Ural Mountains; 2) Northeastern China, east of the Mongolia Plateau and, 3) South-west of the Kamchatka Peninsula. The first most active area is related to European cyclones (Schinke, 1993) and starts in the lee of the Ural Mountains; the second is related to cyclones in the lee of Altai-Sayan and the third to East Asian coastal cyclones. After zonal averaging, two frequency maxima of deep cyclones emerged, one between 62.5–67.5° N and the other between 47.5–52.55° N. This is different from the European and North Atlantic regions where only one maximum occurs. The seasonal frequency deep cyclones in Northeastern China reaches maximum in spring and summer while in western Siberia and the Northwest Pacific deep cyclones are more frequent in winter. The annual trend of deep cyclones over the Northwest Pacific shows an increase from the sixties to the eighties while deep cyclones over East Asia decreased during this period. In the 1980's, more deep cyclones occurred over the Northwest Pacific and less deep cyclones over main land Asia which may be associated with the northern hemisphere warming. The monthly number of oceanic deep cyclones in December and January appeared to be positively correlated with the August and September sea surface temperatures over the East Pacific (El Nino regions 1 + 2).