夏季のアジア・西太平洋の偏西風帯にみられる季節内変動について

Abstract

From the analysis of intraseasonal variations on the subtropical westerly over the Asiatic Continent and the Pacific Ocean in summer season using ECMWF objective analysis data during 1980 to 1985, it is confirmed that standing westerly wave activities are seen in many years.From EOF (Empirical Orthogonal Function) analysis and lagged correlation analysis, some aspects of the westerly wave activities are shown. Many spatial patterns of EOF components exhibit southward propagation. Northward or east-westward propagations are scarcely seen. This result is consistent with standing features of the westerly wave activities.Lagged correlations between the westerly wave activities and tropical systems, tropical convection and Indian monsoon activities, are calculated. In many cases, significant correlation coefficients are not seen. However, the EOF-1, which shows negative geopotential height correlation between east coast of the Asiatic Continent and the Pacific Ocean east of Japan, has significant lagged correlations with the convective activities around northern peripheral of the ITCZ over the tropical western Pacific Ocean.Furthermore, the EOF-2 has significant correlations with the Indian monsoon activities. It shows that the subtropical westerly east of Asia continent are acceralated several days after active phase of the Indian monsoon activities.