Response And Interact Between Atmospheric Circulation And Temperature Of Eurasian

In this paper,we analyzed global surface temperature and discovered that global warming that started in the late 20^th century exhibited a significant regional character. The speed of warming in Eurasian continent in middle and high latitudes was faster than that in low latitudes,which caused temperature gradient decreasing between middle and high latitudes,and temperature gradient increasing between mid-high latitudes and polar areas.Based on thermal wind theorem,wind speed decreased in middle latitudes and increased in high latitudes,and the northerly component weakened,cold air from the polar region pushing southward was blocked,so the surface temperature in Eurasian continent in middle and high latitudes increased further.The positive feedback process between atmospheric circulation and temperature in Eurasian continent in middle and high latitudes might be the theoretical mechanism of its accelerated warming,and the contribution of this feedback process to warming in Eurasian continent in middle and high latitudes was 26.8%.In the process of studying the response mechanism of atmospheric circulation to accelerated warming in Eurasian continent in middle and high latitudes,we made the following conclusions:1.During 1901～2002,the global warming exhibited a significant regional character. The increase rate of annual mean temperature in Eurasian continent in middle and high latitudes was 0.15℃/10a,a figure that was greatly in excess of 0.074℃/10a as the global mean,and was obviously higher than that of other areas in the world;It was different in different seasons,the rising of mean temperature in winter was fastest,that in spring was next,and that in autumn was the least one.The study showed that the warming in Eurasian continent in middle and high latitudes became increasingly strong in the last 30 years,ranging from 0.87℃/10a to 0.93℃/10a in the 1970s to 1980s,respectively,and the warming rate even exceed 1.00℃/10a since the 1990s. 2.The EOF analysis of zonal-mean atmospheric circulation revealed that the height fields in different layers all exhibited obvious changing trend in the last 60 years. The geopotential height rose in low latitudes and dropped in high latitudes,and the westerly wind strengthened in middle latitudes.3.The synthetic analysis of sea-level pressure fields,500hPa height fields,500hPa flow fields,200hPa and 500hpa zonal wind fields in winter and spring in typical years showed that the atmospheric circulations in higher-temperature years and lower-temperature years were significantly different in Eurasian continent in middle and high latitudes.In the higher-temperature years,sea-level pressure in Eurasian continent in middle and high latitudes was low,cold high intensity weakened;In 500hPa height fields,the polar vortex deepened,the east-Asian deep trough moved eastwardly and shallowed;In 500hPa flow fields,there was cyclonic difference circulation over the Eurasian continent in middle and high latitudes, which was controlled by abnormal southerly and southwesterly.The westerly in middle and high latitudes was stronger,and the northerly component weakened,so cold air activities reduced;In both 200hPa and 500hPa zonal wind fields,the westerly in middle and high latitudes strengthened obviously,whereas subtropical westerly jet weakened.All the analyses above indicated that zonal circulation dominated in atmospheric circulation in higher-temperature years,zonal wind in middle and high latitudes strengthened,the activities of cold air pushing southward weakened,which leaded for higher temperature in Eurasian continent in middle and high latitudes.4.The zonal index in Eurasian region revealed that it has a strong character of inter-annual variability.It exhibited a decreasing trend fi'om the late 1940s to the early 1960s.In the early 1960s,it rose,and then abruptly in the middle 1970s,and after that,it showed a rising trend.Especially since the late 1970s when global warming started,the linear tendency was 0.35/10a.In winter,the standardized zonal index and the temperature in Eurasian continent in middle and high latitudes were positively correlated,and the linear regression coefficient was 0.89,that is to say,when the zonal index increased by a standard deviation,the temperature in Eurasian continent in middle and high latitudes rose by 0.89℃.In spring,the coefficient was just 0.16,it means that zonal circulation affected the temperature in Eurasian continent in middle and high latitudes less obviously in spring than that in winter.5.In this paper,we also did inter-annual analysis of blocking index in Ural region, and showed that blocking exhibited decreasing trend during the past half century. The blocking index in Ural region and the temperature in Eurasian continent in middle and high latitudes were obviously negatively correlated.The decreasing of blocking index in Ural region made cold air pushing southward in polar region weaken,which thus leaded the temperature in Eurasian continent in middle and high latitudes rise obviously.6.We also did multivariate regression analysis of the contribution of various atmospheric circulation factors to air temperature variation in Eurasian continent in middle and high latitudes.The contribution of zonal index to air temperature variation in Eurasian continent in middle and high latitudes is 25%,and the contribution of fitting of many factors can reach to above 50%,and variance contribution of it to mean air temperature variation in Eurasian continent is 26.8%. In addition,we also construct a theoretical linking mechanism between atmospheric circulation factors and accelerating warming in Eurasian continent in middle and high latitudes.