Intraseasonal variations and singularities of surface pressure patterns over East Asia in the Cold, Warm and Variable Periods during the 20 th Century

Abstract

Surface weather charts have been analyzed nearly for one century on a hemisphere scale. The present study tries to demonstrate characteristics of the occurrence frequency of pressure patterns in the global cold, warm, and recent variable periods, which correspond to or are responsible for anomalies in air temperature and precipitation, and to investigate the intraseasonal variations and singularities of pressure patterns over East Asia. This study defines the period from 1906 to 1920 as a cold period, that from 1936 to 1950 as a warm period, and that from 1971 to 1985 as a recent variable period. According to the classification of pressure pattern types by Yoshino (1968), a calendar of pressure patterns during the periods 1906-1920 and 1936-1940 was originally made on the basis of “Daily Synoptic Series, Historical Weather Maps, Northern Hemisphere Sea Level”. The statistics of this study are also based on the calendars for the periods 1941-1950 (Yoshino and Kai, 1974), 1971-1980 (Yoshino and Yamakawa, 1985) and 1981-1985 (original).
The results of this paper are summarized as follows : The annual frequency of the typical winter type (type W) of west high and east low does not reveal much difference between the cold and warm periods. However, in the warm period, the duration of Type W appearance is shorter, but it occurs more frequently in January than in that of the cold period. The typical summer type (Type S), south high and north low, is most distinguished in August, though it is perceptible from July, in the warm period. The temperate migratory high type (Type H) (excluding highs passing North Japan) is clearly eminent throughout the year in the warm period. Particularly in April, Type H accounts for 43% (13% more than that of the cold period); in October it forms 37% (16% more). In the warm period, singularities of Type H are recorded five times in spring and autumn seasons, respectively. The north high type (Type N), which includes migratory highs in North Japan, southern coastal lows and southern coastal fronts, appears with low frequency in the warm period. The difference in occurrence frequency of Type N between the both periods is large in spring (April, May) and autumn (Sept., Oct.). In the cold period when the onset and end of the Baiu season are quite clear, the frontal zone type, consisting of Types N and L, appears with very high frequency (about 90%) throughout the Baiu season. With regard to the typhoon type (Type T), it tends to appear more frequently in August and September of the cold period ; in October of the warm period. Type T appears less frequently in both the summer and autumn seasons of the recent variable periods. Ratios of anticyclonic singularities to cyclonicones are 43 to 57 in the cold period, 54 to 46 in the warm period and 42 to 58 in the recent variable period. In the last period there are many identical singularities with those in the warm period. Especially from mid-August (Aug. 14-18) to mid-September (Sept. 8-12), a series of common singularities-Types T, S, L, S, L and L-are recognized in this order both in the warm and recent variable periods.