Interannual-Interdecadal Variation in Large-Scale Atmospheric Circulation and Extremely Wet and Dry Summers in China/Japan during 1951-2000 Part II: Dominant Timescales

[摘要] Based on the results from the SVD analysis in Part I, here we use wavelet and composite analyses to identify the dominant timescales on which the extremely wet and dry summers in China/Japan, influenced by the large-scale regional atmospheric circulation, may have occurred in 1951-2000. An apparent trend is found in the temporal coefficient of SVD1, with a less significant trend in SVD2. Both trends change sign in the late 1970s. Associated with these trends, the 500 hPa continental high over Eurasia is greatly intensified, with increased 850 hPa northerly wind trends between 100°E-120°E. This circulation change is associated with wet trends in the Yangtze River valley, northern Kyushu and the Pacific side of Tohoku, and dry trends in northern and southern China, Kinki and the Nansei Islands of Japan. All three modes display interdecadal variability, but their cycle lengths and intensities change considerably before and after the late 1970s. The quasi-biennial (QB) signal dominates over the ENSO signal on interannual timescales in all three modes, except for SVD3 after the late 1970s. In SVD2, the QB signal is predominant and modulated on bidecadal and longer timescales. The QB's amplitude peaks in the 1990s. During this decade, the extremely wet and dry summers occurred alternately in the two countries are mainly on the QB timescale of SVD2, but also modified by other timescales and other modes. Our results suggest that the timing and the location for an extremely wet/dry summer to occur be largely determined by the interaction and reinforcement among the dominant timescales of the dominant SVD modes. Since the regional large-scale circulation is better predicted at one season lead than summer rainfall, the spatial and temporal relationships found in this work may help explore possible deterministic causes of spatial/temporal covariability in circulation and rainfall, leading to improved regional climate forecast.

[学科分类] 大气科学