An optimal index for measuring the effect of East Asian winter monsoon on China winter temperature

Extreme cold events occur frequently in China. The authors define a representative yet simple index to reveal the monthly changes in China winter temperature associated with the East Asian winter monsoon (EAWM), which is represented by both the leading empirical orthogonal function (EOF) mode and the country-mean temperature index of Chinese 160 gauge stations. A combined technique of correlation and multivariate EOF (Corr-MVEOF) analyses is applied to capture the dominant coupled patterns of EAWM circulation system. Based on the atmospheric circulation features captured by the leading Corr-MVEOF mode, a new EAWM index referred to as CNWMI is derived by using a stepwise regression analysis. The CNWMI highlights the importance of (1) the Mongolia-Siberian High (MSH) and its southward expansion and (2) the Asia-wide meridional dipole anomaly of 500 hPa geopotential height. Compared with the 27 existing EAWM indices, the CNWMI not only best represents the leading modes of both EAWM circulation system and China winter temperature, but also reasonably tracks the intraseasonal-to-interdecadal variations of EAWM so that the monthly intensity of EAWM can be monitored conveniently. In particular, the Aleutian low (AL) is not strongly related to the MSH and may not be responsible for the variability of EAWM/MSH. Moreover, the indices that are highly correlated with the temperature over southern East Asia do not show significant relationships with the AL, which is different from the conventional concept that a strong EAWM/MSH is linked to a deepened AL. In contrast, the anomalous Australia-Maritime Continent low is in good agreement with the variation of EAWM/MSH.