Five-year Cycles of Summer Weather in Northern Japan after 1980s

Abstract

　Summer weather in northern Japan since the 1980s appears to exhibit a distinct five-year cycle, with the pressure difference between Wakkanai and Sendai (PDWS) as an index of this climatic variability. The temporal variation in the June-August mean PDWS in the period 1982 to 2001 progresses through four cycles, each with conspicuous similarities such as a peak PDWS in the second year of each cycle. The temperature also progresses in similar five-year cycles, varying inversely to the trend in the PDWS. The correlations between the seasonal variations in the PDWS and sea-surface temperature indicate that in the summer following an El Niño event, the PDWS tends to become positive and a cool summer ensues. The progression of the difference in sea-surface temperature between the South China Sea and east of the Philippines exhibits similar temporal variations to the PDWS, and may play an important role in the sudden change from cool summer to hot summer in northern Japan.