资源环境科技发展态势分析平台

Past results [Thompson and Wallace in Geophys Res Lett 25(9):1297-1300, 1998; Science 293(5527):85-89, 2001; Wallace and Thompson in J Clim 15(14):1987-1991, 2002a] indicate that over the Eurasian continent, North America, and East Asia, wintertime surface temperatures tend to be warmer (colder) on high-index (low-index) Northern Hemisphere annular mode (NAM). However, a linear correlation is neither necessary nor sufficient to establish causality between them. Here, we apply a recently developed method, convergent cross mapping (CCM), to examine the causal connections between NAM and wintertime surface air temperature (SAT) over Northeast Asia. Our analysis indicates that both NAM and SAT exhibit nonlinear dynamical structure and that NAM information is encoded in the SAT data but not the other way around. This indicates a causality between them in the direction NAMSAT. This result opens the possibility to use the NAM index as the external driving factor to forecast winter SAT over Northeast Asia.