Variabilities of the Stratospheric Polar Vortex and the Influenceon the Weather of China during the Boreal Winter

NCEP reanalysis datasets are used to analyze planetary wave activity in the Northern Hemisphere that occurs during the stratospheric abnormal processes and associated characteristics of weather variations over China based on selected strong and weak polar vortices according to the Northern Hemispheric annular mode (NAM) index. The analysis reveals that a downward wave coupling event occurs prior to the strong polar vortex events. During this period, the planetary wavenumber1 is reflected to the troposphere, the polar wave guide weakens, and the low-latitude wave guide strengthens. Meanwhile, the E-P flux vector in the middle-high latitudes spreads from the stratosphere to the troposphere. Following the strong polar vortex events, the polar wave guide strengthens, and the low-latitude wave guide weakens to some extent. The upward wave coupling event that occurs prior to the weak polar vortex events strengthens the polar wave guide. Following the events, the planetary wave-1 and the polar wave guide both weaken, and in accordance, the weather of China changes dramatically. Prior to the stratospheric vortex intensification events, temperatures in most parts of China are cooler than normal. The southern region of China is wetter, whereas northwestern Xinjiang and western Yunnan Province are drier. Following the events, the East Asian winter monsoon becomes stronger, and the cold air spills southward. The precipitable water vapor in southern China decreases and the northwestern region of Xinjiang remains dry, whereas most parts of Yunnan become wetter. In contrast, prior to the stratospheric vortex weakening events, the East Asian winter monsoon is significantly strengthened, the temperature of China is colder than normal, and precipitable water vapor clearly decreases. Following these events, temperatures in China increase sharply, and precipitation in central and eastern China and in northwestern Xinjiang increases significantly.