Both the Siberian high and the East Asian trough play crucial roles in the East Asian winter climate system.Changes in the strength and position of the Siberian high can lead to the movement of cold or warm air masses over the East Asian continent,while variations in the East Asian trough can influence circulation patterns in the western Pacific.These combined effects can alter temperature and precipitation distributions in East Asia during the winter,significantly impacting the winter climate.This study defines the Siberian High (SH) index,the East Asian Trough (ET) index,and a Meridional Wind (V index) index between the high and low-pressure systems based on climatological characteristics.The relationships between these indices are explored using power spectrum analysis and linear regressions.The study investigates the significant periods of variability and the impact mechanisms of the Siberian high and East Asian trough on winter temperatures in East Asia.Additionally,a simple linear regression model is constructed using a non-filtering method and cross-validation for extended-range forecasts of intra-seasonal temperatures in southern China during the winter.The main conclusions are as follows:The most significant periods of the SH and ET indices occur on intra-seasonal timescales,accounting for 60％ of the total standard deviation.Power spectrum analysis results show that the energy peaks of the SH and ET indices are concentrated in the 10—50-day period,while the V index is more concentrated in the 10—40-day period.On the intra-seasonal timescales,the correlation coefficients between the SH/ET indices and the V index are 0.69 and -0.73,respectively (through a 99％ confidence test).The reconstructed meridional wind fields related to the SH/ET indices are used to calculate the ratio of the standard deviation compared to the actual meridional wind field.Quantitative results show that the contributions of the intra-seasonal SH and ET indices to the V index are 82.6％ and 42.2％,respectively.Lead-lag regression analysis for the SH,ET,and V indices shows similar regression patterns,with slow eastward propagation of northwest-southeast distributing wave trains in the 500 hPa geopotential height field,consistent configurations of the low-level 850 hPa moisture,near-surface 925 hPa circulations,precipitation,and 2 m temperature fields.The three indices all correspond to a northwest-southeast-oriented low-frequency Rossby wave train in the middle and higher troposphere,which propagates eastward or southeastward.The upper-level circulation fields are well linked to low-level water vapor,precipitation,and surface air temperature fields.When the Siberian high deepens or the East Asian trough develops,northerly winds are enhanced over the key East Asian region,facilitating the transport of dry and cold air from high latitudes in Siberia to East Asia,resulting in dry and cold weather conditions.Based on comprehensive regression results,the V index and the intra-seasonal component of 2 m temperature during winter in southern China are selected as the predictors and predictands.A linear regression model is built for extended-range forecasting,and the forecast performance is evaluated by calculating the time correlation coefficient and standardized root mean square error.Cross-validation and independent forecast experiments indicate that reliable forecasts of the intra-seasonal 2 m temperature in the region with a lead time of 25 days can be achieved.