We newly define here Winter Monsoon Index (WMI) as the ormalized anomalies of the winter SLP difference between the two eastern centers of action of the EU1 pattern. Our sign convention of the index results from that of the SLP difference, that is, the SLP at the center of the East Sea minus the SLP west of Lake Baikal, Siberia, namely: SLP difference=SLP (40N, 135E) - SLP (45N, 95E).

The correlation coefficient between WMI and Korean winter air temperature from these high-pass (<20 years) filtered time series is 0.62. This already high correlation increases further up to 0.82 when data more recent than 1967 are used. For comparison, the correlation coefficients for unfiltered original time series are slightly lower: 0.57 for full data and 0.78 for partial data posterior to 1967. All these coefficients are significant at a confidence level of 95% or more. It is the first time such a good relationship has been obtained between a weather parameter and an atmosphere circulation index over the Korean Peninsula.

The Korean winter air temperature is under strong control of the winter monsoon, especially for the 2-4 year interannual variability having a predominant quasi-biennial periodicity of 2.3 years.