Abstract:

Using the daily NCEP/NCAR reanalysis data and the temperature data of the National Meteorological Information Center, the typical low-temperature rain and snow events in China from January 26 to February 4, 2018, were analyzed.The results show that before the occurrence of low-temperature rain and snow, the polar vortex begins to shrink to the west and gradually becomes elliptical.Affected by the abnormal enhancement of the polar vortex, the cold air is strengthened to the south.The high-pressure ridge forms about 15 days before the low-temperature rain and snow, and develops into a stable and powerful Siberian high-pressure over the Ural Mountains region, which continuously strengthened and moved eastward over the northern Eurasia continent.Two days before the occurrence of low-temperature rain and snow, two abnormally southerly air streams of 850 hPa wind field cooperate with the abnormal water vapor transport, and the positive anomaly of the geopotential height at 500 hPa of the upper Ural Mountains in the northeast-southwest direction and gradually weakened, resulting in the accumulation of a large amount of cold air in the abnormally strong cold center of Siberia and southward.It provides favorable conditions for the low-temperature rain and snow weather in China.

Key words: Low-temperature rain and snow, Siberian high, Polar vortex