Interdecadal changes in winter surface air temperature over East Asia and their possible causes

Using ensemble empirical mode decomposition (EEMD) for detecting the interdecadal changes in the East Asian winter monsoon (EAWM), this study identifies that the intensity of the EAWM experienced remarkable transition around mid-1980s and late 2000s: a strong period (P1, 1960-1986), a weak period (P2, 1987-2007), and a strong period (P3, 2008-2015). A distinctive cold (warm) surface temperature anomaly is found over the Eurasian continent including East Asia, and cold (warm) sea surface temperature (SST) anomalies are present over the North Pacific (NP) during P1 (P2). In contrast with P1, the EAWM is characterized by a large temperature difference between Eurasian continent and NP, and a negative Pacific Decadal Oscillation (PDO)-like SST anomaly pattern is found over the NP during P3. During three periods, the Siberian high (SH) plays an important role in deciding the intensity of the EAWM. In addition, the EAWM exists under the influence of an enhanced atmospheric circulation associated with a positive North Pacific Oscillation (NPO) and a negative PDO during P2 and P3, respectively. Accordingly, to recognize the relative importance of each combined effect which it differs for times, the combined effect of SH and NPO (SH and PDO) variability on the weakening (strengthening) EAWM is explored during P1 and P2 (P2 and P3). Consequently, while the atmospheric variabilities of SH and NPO bring about the weakening of EAWM after the mid-1980s, the SST variability related to PDO with the SH variabilty is involved in the strengthening of EAWM in recent decade.