An index of East Asian winter monsoon applied to description the Chinese mainland winter temperature changes

Using the NCEP/NCAR reanalysis data (Version 1) and the observation data of China from January 1951 to February 2007, a new index of East Asian winter monsoon circulation (IEAWM) was defined based on comparison of previous different winter monsoon indices and circulation factors influencing the winter climate over china. Its relationships with winter temperature over China and large-scale circulation were analyzed. Results show that new index represents very well the winter temperature over China and the East Asia winter monsoon (EAWM) system. This index reflects the integrated effect of the circulations over high and low latitudes and the thermal difference between the continent and the ocean. While in the previous studies, most monsoon indices only describe the single monsoon member. The IEAWM is a good indicator of the intensity of the EAWM. Positive values of IEAWM correspond to strong EAWM, stronger than normal Siberian high and East Asian trough, and the strengthening of the meridional shear of 500 hPa zonal wind between high and low latitudes over East Asia, and therefore, the southward cold advection becomes strong and leads to the decrease in surface temperature over China; and vice versa. The obviously interdacal change is found in the IEAWM that it is positive before the mid1980s, but negative since the mid 1980s, in good agreement with the fact of the winter warming in China after 1985.