The Eurasian teleconnection pattern （EU） is an important low-frequency pattern with well-known impacts on climate anomalies in Eurasia. The difference of low-level v-winds in several regions in the Eurasian mid-high latitudes is defined as the EU index （EUIv）. In this study, the relationship between the winter EUIv and precipitation in the following summer over China is investigated. Results show that there is a significant positive （negative） correlation between the winter EUIv and the following summer precipitation over North China （the Yangtze River-Huaihe River basins）. Meanwhile, an interdecadal variability exists in the interannual relationship, and the correlation has become significantly enhanced since the early 1980s. Thus, the proposed EUIv may have implications for the prediction of summer precipitation anomalies over China. In positive winter EUIv years, three cyclonic circulation anomalies are observed--over the Ural Mountains, the Okhotsk Sea, and the subtropical western North Pacific. That is, the Ural blocking and Okhotsk blocking are inactive, zonal circulation prevails in the mid-high latitudes, and the western Pacific subtropical high tends to be weaker and locates to the north of its normal position in the following summer. This leads to above-normal moisture penetrating into the northern part of East China, and significant positive （negative） precipitation anomalies over North China （the Yangtze River-Huaihe River basins）, and vice versa. Further examination shows that the SST anomalies over the Northwest Pacific and subtropical central North Pacific may both contribute to the formation of EUIv-related circulation anomalies over the western North Pacific.
The cold vortex is a major high impact weather system in northeast China during the warm season, its frequent activities also affect the short-term climate throughout eastern China. How to objectively and quantitatively predict the intensity trend of the cold vortex is an urgent and difficult problem for current short-term climate prediction. Based on the dynamical-statistical combining principle, the predicted results of the Beijing Climate Center＇s global atmosphereocean coupled model and rich historical data are used for dynamic-statistical extra-seasonal prediction testing and actual prediction of the summer 500-hPa geopotential height over the cold vortex activity area. The results show that this method can significantly reduce the model＇s prediction error over the cold vortex activity area, and improve the prediction skills. Furthermore, the results of the sensitivity test reveal that the predicted results are highly dependent on the quantity of similar factors and the number of similar years.
In this paper we try to extract stable components in the extended-range forecast for the coming 10–30 days by using empirical orthogonal function （EOF） analysis, similarity coefficient, and some other methods based on the National Center for Environmental Prediction （NCEP）/National Center for Atmospheric Research （NCAR） reanalysis daily data. The comparisons of the coefficient of variance of climatological background field and truth data in winter between 2010 and 2011 are made. The method of extracting stable components and climatological background field can be helpful to increase forecasting skill. The forecasting skill improvement of air temperature is better than geopotential height at 500 hPa. Moreover, this method improves the predictability better in the Pacific Ocean. In China, the forecast in winter in Northeast China is more uncertain than in the other parts.
