An Analyzing Study of the Anomalous Activity of Blocking High over the Ural Mountains in January 2008

Some studies have indicated that the continued activity of blocking high over the Ural Mountains plays an important role in the occurrence of the freezing rain and snow storm in South China during January 2008. To understand the anomalous activity of blocking high over the Ural Mountains further, this study will analyze the possible causes for this phenomenon from the aspects of the tropospheric Arctic Oscillation (AO), the stratospheric polar vortex, and the sea surface temperature anomalies, using the daily NCEP/NCAR reanalysis data and the Hadley center HadISST1 data. The analyses results show that the Ural blocking high in January is significantly related to the AO and the stratospheric polar vortex during 1958－2007. However, the situation for 2008 does not fit in with such close relationship in the past 50 years, and the relation is opposite to that in the past 50 years. It means that the Ural blocking high in January 2008 is not closely related to the AO and the stratospheric polar vortex in the 2007－2008 winter. Further analyses indicate that the Ural blocking high is closely related to the positive sea surface temperature anomalies (SSTA) in the North Atlantic, particularly in the subtropical North Atlantic area, but not to the La Niña in the Pacific. The positive SSTA in the North Atlantic (especially in the subtropical North Atlantic) may act as one of the major external forcings for the anomaly of Ural blocking high.