Possible Causes of Circulation Anomalies Associated with Subsequent Snowstorms over the North of Xinjiang during Winter 2009
2009年冬季新疆北部持续性暴雪的环流特征及其成因分析

The anomalies of moisture flux and atmospheric circulations linked to the subsequent snowstorms occurring in Altay area of Xinjiang during winter 2009 are discussed on the basis of station-observed and NCAR/NCEP reanalyzed data sets, and the possible causes associated with ENSO and Arctic Oscillation (AO) are addressed in the framework of historical analog analysis. Results suggest the enhanced anomalous cold trough in the west of Lake Baikal is a critical circulation system, and its maintenance resulted in the west cold surge moving southward, meeting the southwest warm and wet air coming from the Caspian Sea in North Xinjiang, and caused the successive snowstorms. Correlation analysis suggests that the enhanced anomalous cold trough over the west of Lake Baikal is closely related to the weakened AO index. In negative AO index phase, the 500-hPa geopotential height around Lake Baikal decreases, a meridional circulation anomalies pattern prevails in the Northern Hemisphere, which maintained the Ural blocking high and gave rise to the southward moving clod surge along the west of Lake Baikal, and results in the successive cold waves and snowstorms in the north of Xinjiang. Analysis suggests that during the El Ni o year, the enhanced western North Pacific subtropical high results in the southeast moisture flux, but the northward component could not arrive in North Xinjiang, therefore the El Ni o event possibly has little benefit to the successive snowstorms in this area.