冬季北半球における下層寒気の時空間変動の季節的な位相固定

Abstract

The climatological features of temporal and spatial variations of large-scale circulation and lower cold air (LCA) in the winter northern hemisphere are investigated using 9-year mean temperature and geopotential height data, from 1980 to 1988. The large-scale circulation pattern abruptly changes in late December (the 70th pentad) and mid-February (the 9th pentad), and shows a more meandering pattern in the period between these two pentads. We define this period as the climatological 'midwinter' in the northern hemisphere. During midwinter, LCA regions lying around the eastern part of Siberia and the Northwest Territories of Canada exhibit periodical and phase-locked variations with periods of about 25-35 days. The phase-locked migration patterns of three major LCAs in the eastern part of Siberia, Northwest Territories of Canada, and Scandinavian Peninsula in midwinter are investigated using the composite maps of 850 hPa temperature anomaly. The LCA over the Scandinavian Peninsula migrates from the high cyclonic activity area in the North Atlantic to the north side of the Tibetan Plateau. The LCA in Siberia is formed periodically with large temperature variation and migrates to the Central Pacific. The LCA over the North American Continent spreads in the meridional direction. The phaselocking of LCA movement is closely related to the appearances of some natural seasons and singularities in Japan.