China Freezing Rain Genesis Potential Index And The Decadal Variation Of Freezing Rain

By using the GTS surface and upper-air observations over China and 52-year Freezing Rain (ZR) daily observations from National Meteorological Information Center, the features of meteorological elements during ZR events in China and its decadal variation is analyzed, from the two aspects of the short-term and long-term forecasts. The results are as follows.The surface temperature, surface depression of dew point temperature and temperature in the upper air are the basic characteristics of meteorological elements for ZR. It is found that during ZR, the surface temperature is usually -7.3～0.9℃; The surface depression of dew point temperature is 0～3.9℃. The temperature fluctuates in the lower troposphere and then decreases with elevation. Based on that, a freezing rain genesis potential index (FRGPI) is defined to indicate the possibility of freezing rain occurrence. The accuracy is tested. The result illustrates that the accuracy rate of each station is above 90% and the process of freezing rain events can be indicated well. The accuracy can be much higher if combine FRGPI with precipitation, which is benefit for freezing rain disaster prevention and mitigation. By using reanalysis and forecast data, a further development and application of Freezing Rain Genesis Potential Index is given. The ZR processes can be detected with higher precision and the freezing rain can be forecasted 10 days before.By analyzing the total number of yearly ZR occurrences, it is found that ZR has significant decadal variations. The amplitude of ZR variation during 1962-1979 was larger than that of 1980-1996. There was a remarkable decadal regime shift around 1997. According to the background atmospheric circulation during ZR, it is found that the 500hPa Geopotential Height anomaly of Ural Mountains is high, the area from Lake Baikal to Northern China is low and China east and south costal district is high, which showed a ’+-+’ pattern. The background atmospheric circulation changed a lot after 1997, which is mainly an out-of-phase seesaw pattern between the south and the north. The pattern is also notable in the background atmospheric circulation in winter during the year with more ZR.The relationship between sea surface temperature (SST) or sea ice concentration (SIC) and ZR is also been discussed. It can be found that ZR was mainly influenced by the sea ice of Barents Sea and Kara Sea during 1962-1979, by SST of North Atlantic Ocean and the area near Kamchatka Peninsula during 1980-1996 and by sea ice of Pacific Arctic and SST near Kamchatka Peninsula during 1997-2013. Combining with the atmospheric circulation, the mechanism of how the SST and sea ice influence the ZR occurrences is studied. ECHAM5 model is used to study the relationship between the Pacific Arctic sea ice and China Freezing Rain, it is found that the decrease of the Pacific Arctic sea ice do cause the increase of China Freezing Rain disasters.