【作者】 季明霞；

【导师】 黄建平；

【作者基本信息】 兰州大学 ， 气象学， 2009， 博士

【摘要】 本文通过对全球地表气温的分析,发现上世纪末开始的全球变暖表现出了很强的区域性。欧亚中高纬度地区增温速度明显比低纬度地区增温快,造成中高纬之间温度梯度减小,中高纬度与极地间温度梯度增加。根据热成风原理,中纬度风速减小,高纬度风速增加,极地南下冷空气受到阻挡,从而造成欧亚中高纬度大陆地表气温进一步升高。大气环流与欧亚中高纬度大陆气温之间的正反馈过程可能是欧亚中高纬度大陆加速增温的理论机制,这一反馈过程对欧亚中高纬度大陆增温的贡献为26.8%。在探索东亚大气环流对欧亚中高纬度大陆加速增温的响应机制的过程中,得到以下主要结论:1、近百年来,全球变暖表现出了很强的区域性特征。欧亚中高纬度大陆区域年平均气温增温速率为0.15℃/10a,远大全球平均增温速率(0.074℃/10a),也明显高于全球的其他地区;从季节增温情况来看,冬季增温最快,春季次之,秋季最小。而且研究表明近30年来欧亚中高纬度大陆增温速率明显加快,70年代以来增温速率为0.87℃/10a,80年代以来增温速率增加到0.93℃/10a,而90年代以来增温速率超过1.00℃/10a。2、对北半球纬圈平均的大气环流进行EOF分析,表明近60年各层高度场均表现出了明显的变化趋势,低纬位势高度上升,高纬位势高度下降,中纬度西风加强。3、通过对冬春两个季节气温典型年份的海平面气压场、500hPa高度场、500hPa流场、200hPa及500hPa纬向风场的合成分析发现,气温偏高年与气温偏低年的大气环流在欧亚中高纬度大陆表现出了显著差异。气温偏高年,欧亚中高纬度大陆海平面气压偏低,冷高压强度减弱;500hPa高度场上极涡加深,东亚大槽东移且变浅,大气环流经向度减弱;500hPa流场上,欧亚中高纬度大陆上空为气旋式差值环流,其受异常的南风或者西南风控制,中高纬度西风较常年偏强,北风分量减弱,冷空气活动较少;200hPa及500hPa纬向风场上,都表现出中高纬度西风显著增强,而副热带的西风急流则减弱。以上分析表明,温度偏高年,大气环流以纬向环流为主,中高纬度纬向风加强,南下的冷空气活动减弱,造成了中高纬度欧亚大陆的温度偏高。4、通过对欧亚区域西风环流指数的计算发现,该指数具有很强的年代际变化特征,40年代末至60年代初为下降趋势,60年代初上升,70年代中期,突然下降,此后一直呈现波动中上升的趋势,尤其自70年代末全球变暖以来,西风指数的线性趋势为0.35/10a。冬季,标准化的西风指数与欧亚中高纬度大陆气温之间为显著的正相关,其线性回归系数为0.89,也就是说当西风指数增加一个标准差时,欧亚中高纬度大陆区域平均气温偏高0.89℃。春季的回归系数仅为0.16,说明春季欧亚中高纬度大陆气温受西风环流影响不如冬季显著。5、本文还对乌拉尔山区域的阻塞高压指数进行了年代际分析,发现半个多世纪以来阻塞高压呈现下降的趋势。乌拉尔山地区的阻塞高压指数与欧亚中高纬度大陆气温之间负相关显著。多年来乌拉尔山阻塞高压的减少使得极地南下冷空气减弱,造成欧亚中纬度大陆的气温升高显著。6、文中最后将各个大气环流因子对欧亚中高纬度大陆气温变化的贡献进行了多元回归。其中,西风指数单个因子对欧亚中高纬度大陆气温变化的方差贡献为25%,多个大气环流因子对欧亚中高纬度大陆气温变化总的方差贡献最高可达50%以上,对欧亚大陆的气温变化的区域平均方差贡献率为26.8%。另外,还构建了大气环流因子与欧亚中高纬度大陆加速增温之间的理论联系机制。更多还原

【Abstract】 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.更多还原