Analysis On Circulation Anomalies During Extreme Freezing Rain And Snow Disasters In Southern China

In the context of the global warming, with extreme weather and climate events increasing frequently, the living environment and quality of life of human are threated by the extreme weather events. Extreme weather and climate tend to have longer continuous, causing serious meteorological disasters. The snow disaster occurred in January 2008 South China, that is, the performance of persistentclimate anomalies.Using Daily meteorological data from 1951 to 2008 on stations of seven provinces in southern China, the intensity standards for freezing wheather is developed,19 cases is Selected. The circulation of 36 extreme freezing rain and snow events of the 19 years in southern China was analyzed using daily NCER/NCAR 2.5°×2.5°daily reanalysis data. Four weather patterns were summarized as follow:ridge emerged in north accompany with groove in south; the Ural type; horizontal groove with southern branch type and higher latitudes vortex type. The results shows:1,Strong cold air from the North and the abundant water vapor from the south branch maintain, while the western Pacific subtropical high ridge line on the strong side is more conducive to the south west trough of water vapor transmission. Horizontal groove with southern. branch type and higher latitudes vortex type continued long and caused frozen rain and snow weather very easily.2,The physical parameter fields of those processes were also analyzed. The result revealed that the convergence center at 850-700hPa became obvious on 1～2 days advanced the vertical speed center, forebode the increase of freezing rain and snow. In the serious freezing disaster year, a warm layer (temperature>0℃) often occurred at 700hPa, and southwest jet provided water vapor and heat for the maintenance of freezing rain. There is a strong vertical shear on the stacked high and low level jet stream, enhanced tropospheric ascending motion. Strong convective situation paly an important role on the development of frzeeing rain and snow weather.3,Strong freezing rain and snow disaster in southern China mostly occurred in the context of La Nina years.Ural blocking continue high pressure and the Western Pacific persistent anomal, India and Burma slots remain strong, combinations of these types of atmospheric circulation anomalies is the direct reason for continued freezing rain and snow disasters in the South.Strong cold air south to invasion the Yangtze River Basin and its southern region, make snow disaster. Thongh winter Monsoon weather have a major impact for the South, is not necessarily hazard.The intensity and direction of Origin winter monsoon make great effects to winter precipitation in the south together.On the basis of the index of East Asian winter monsoon combined with standard of freezing rain and snow years, selected disaster years of weak and strong wind. The average state of the winter based on a total of 50 years from 1948/49 to 2007/08. Analysis of the atmospheric circulation difference between strong and weak winter monsoon years with snow disasters. The results shows:1,Strong (weak) winter monsoon during the winter deepened (weakened) the East Asia trough, temperature anomalyis negative (positive) near the Sea of Japan, and the temperature decreases (increases), the gradient strengthened (weakened) north of 25°in southern China. The north cold air southward in greater degree of convergence in strong winter monsoon year. China's mainland coast from latitude to low latitude areas are controlled by strong northerly winds, the longitude direction of the wind since Bohai Sea to the South China Sea area is very significant. In weak winter monsoon year, the downdraft northward about 5 degrees of latitude with the southerly difference significant. The wind vectors in 5～20°N latitude belt close to the east wind. Anticyclone difference circulation appears near the Philippines.2,The water vapor transport flux from the ground to the 300hPa in weakwinter monsoon years greater than strong years. In the north longitude direction, around South China Sea andIndo Peninsula the wind transported significant. The maximum water vapor flux of the easterly winds on the belt is also greater than strong years in the lower latitudes. It turns to south wind in 700hPa in the weak year while turns 600hPa in the strong year.3,PT index can reflect the freezing rain and snow disaster years southern China. The South China region from the ground to the bottom of the troposphere, PT was positively correlated with the north wind component, but in the middle and lower troposphere has a strong positive correlation southerly component.4,The SST of South Indian Ocean in June was related to the following year in January of PT index. SAM index in April has positive correlation coefficient of 0.5 or above that year in June of the Southern Indian Ocean.The Antarctic Oscillation influence Southern Indian Ocean two months ahead. The sea surface temperature anomaly elevated, snow disaster happen the following year.This article summarizes the the weather patterns and the physical elements in snow disaster years in south China, also the reasons for the occurrence and maintenance of freezing weather. Analysis on the abnormal characteristics of the members of East Asian winter monsoon system. The next step will use the model to explore mechanism in depth to provide a theoretical basis for the snow disaster forecast, decrease the influence of extreme weather events on people's lives.