Interdecadal Spatial-Temporal Change Trend of East Asian Winter Monsoon in the Last 40 Years
近40年来东亚冬季风的年代际时空变化趋势

The spatial-temporal characteristics of the interdecadal change(IC) of East Asian winter monsoon(EAWM),represented by sea level pressure(SLP),and surface air temperature(SAT) in winter during the period of 1961-2000 and their relationship are studied based on NCEP/NCAR reanalysis data and using some statistic methods,such as running mean,correlation analysis and empirical orthogonal function-singular value decomposition(EOF-SVD) compositive analysis.The basic clue of EOF-SVD compositive analysis is(1) decomposing SLP and SAT in winter by EOF respectively to gain their principal spatial structure,i.e.,the first eigenvectors,and temporal change trends,denoted by the corresponding time coefficients(TC),as well as the relationship of their spatial-temporal changes;(2) using SVD of SLP and SAT in winter to investigate their spatial remote correlations if the close relation is found in step 1.Results suggest that using the EOF of SLP to investigate the variety of EAWM is reasonable and superior to EAWM index defined by regional mean,because it can attain the spatial structure of SLP,which simultaneously includes the information of the intensity and southward extending of EAWM.According to the EOF results,it is found that on interannual scale,EAWM exhibits an overall weakening trend in the past 40 years.By means of EOF-SVD compositive analysis on interdecadal scale,the results show that the first eigenvector of interdecadal component(FEIC) of SLP in winter displays a spatial structure with "negative in north and positive in south" over East Asia and positive anomalies over the sea.A turning from negative to positive happens to the TC of the first eigenvector in the late 1970s,reflecting the interdecadal weakening of intensity and southward extending of EAWM.The FEIC of SAT in winter exhibits a spatial distribution with distinctive warming over middle-high latitude land and little change over low latitude land and sea.A turning from negative to positive for the TC also occurs in the early 1980s,suggesting an interdecadal decreasing trend of sea-land thermal difference(SLTD) in middle-high latitudes and an interdecadal increasing trend of SLTD in low latitudes.The spatial-temporal changes of the above two meteorological elements are in accordance,indicating the close correlation between the interdecadal spatial-temporal changes of EAWM and SAT in winter.The results of SVD indicate that the interdecadal corresponding relationship between SLP and SAT in winter over land is more significant than that over sea,suggesting the IC of EAWM may be associated with the regional response of the climate in East Asia to the heterogeneous spatial structure of global warming.