Interdecadal Variation Of Extreme Low Temperature And Snowstorm In Northern China In Recent 50 Years And Possible Causes

Based on daily air temperature data and daily precipitation data from "Daily Surface Climate Variables of China" and gridded database from 1961 to 2011,the interdecadal variation in the relationship between North Atlantic Oscillation(NAO)and extreme low temperature,and the interdecadal variation of the snowstorm in Northern China and possible causes are analyzed based on correlation analysis,regression analysis and other statistical methods.The main conclusions are as follows:(1)The feature of interdecadal variation in cold days(nights)in Northern China is obvious in recent 50 years.Cold days(nights)are more frequent before the middle 1980s compared to that after the middle 1980s.And the relationship between NAO and cold days(nights)have remarkable interdecadal variation.Before the middle 1980s,NAO anomalies have a significant effect on cold days(nights)in Northeast China(NEC)in late winter,but the effect becomes weak after the middle 1980s.It is found that the interdecadal variation in the relationship between NAO and cold days(nights)in NEC in January is largely attributed to the NAO-related atmospheric circulation anomalies under the different interdecadal backgrounds.The weather systems such as cold vortex caused by the NAO-related atmospheric circulation anomalies can maintain over a large area from Lake Baikal to NEC,leading to lower than normal temperature and more frequent cold days(nights)in NEC during the period of 1969-1988 when there is significant correlation between NAO and cold days(nights)in NEC.The opposite is true during the period of 1989-2009.(2)The snowstorm in Northern China shows an increasing trend and also an obvious interdecadal variation in recent 50 years.It is less frequent before the middle 1980s,begins to increase after the middle 1980s,and occurs more frequently during the period of 2002-2011.The high frequency of snowstorm is mainly located in NEC,and its spatial distribution shows an increasing trend from Northwest to Southeast,and the interdecadal variation of snowstorm in NEC is also obvious.Snowstorm in NEC is less frequent during the period of 1964-1988,but becomes more during the period of 2002-2011.The atmospheric circulation characteristics of the interdecadal variation of snowstorm in NEC are analyzed.It is found that there is less water vapor transported to the NEC during the period of 1964-1988,but more water vapor transported from the Northwest Pacific Ocean to the NEC in the last 10 years(2002-011).Meanwhile,the polar cold air southward as well as the warm moisture of the Pacific Ocean northward ultimately contributes to form the convergence frontogenesis in NEC,providing the dynamic conditions for the frequent occurrence of snowstorm,and leading to the interdecadal increase of snowstorm in NEC.Furthermore,it is found that the interdecadal variation of snowstorm in NEC is closely related to NAO.(3)The autumn Arctic sea ice shows a significant interdecadal variation in recent 50 years,with more sea ice during the period of 1964-1988,but less during the period of 2002-011.And there is a good correlation between the interdecadal decrease of Arctic sea ice and the interdecadal increase of snowstorm in NEC.Moreover,the atmospheric circulation anomalies mainly show as the weakening of zonal westerly winds and the negative phase of the NAO caused by the reduction of Arctic sea ice,leading to the increase of meridional winds,and to the benefit of the polar cold air southward invasion,and the interdecadal variation of extreme low temperature in Northern China.The frontogenesis induced by polar cold air and the warm moisture results in the interdecadal variation of snowstorm in Northern China.We hold that the decline of early autumn Arctic sea ice has played a critical role in the increase of snowstorm in Northern China,especially the interdecadal increase of snowstorm in NEC.