Influences of the Deflection of Stratospheric Polar Vortex on Winter Precipitation of China

Using NCEP/NCAR reanalysis data and monthly precipitation data of 160 stations in China from 1970 to 2010 provided by National Climate Center, the deflection intensity variation of the stratospheric polar vortex, which moves toward the Eurasia, is analyzed and the relationship between the deflection intensity indexes in winter and the precipitation in the corresponding and later period is also studied by means of wavelet analysis, correlation analysis, composite analysis and so on. Results show that there is a dominant interannual oscillation period of about 6—8 years for the deflection intensity indexes. The interannual oscillation period is roughly 8 years from the 1970s to the mid and late 1980s, but it shortens to 6 years from the late 1980s to the early 2000s. Positive phase oscillation occurred mainly in the late 1980s, 1990s and recent years.The deflection of the stratospheric polar vortex, which moves toward the Eurasia in January, has a very important impact on precipitation in the same period and later in February. The same period of significant positive correlation between the deflection intensity index in January and precipitation in January mainly occurs in central China and southwest Xinjiang, but significant negative correlation is also found in central Xinjiang. The later period of significant positive correlation between the deflection intensity index in January and precipitation in February is also mainly located in central China, but extends northwestward, making precipitation in north of central China and south of North China relatively reduced, while precipitation in west of North China and east of Northwest China relatively increased.From the analysis of circulation situation background, it can be summarized that strong Eurasian polar vortex in January may lead to reduced East Asian trough and East Asian winter monsoon. The departure of the southeast wind is remarkable in central and eastern China, which is easy for warm and humid air moving toward the northwest of China. The northerly anomaly is remarkable in north Lake Baikal region, which makes cold air and warm air meet to the north of normal situation. Also, lower humid air transmit upward obviously increases, and significant strong convergence center appears in central China. It is found that there is a significant negative correlation between the index of the Eurasian polar vortex intensity and the index of East Asian winter monsoon in January, which passes the test of 0.05 level.