【作者】 李艳；

【导师】 王式功； 金荣花；

【作者基本信息】 兰州大学 ， 气象学， 2010， 博士

【摘要】 从上世纪40年代开始,阻塞高压(或简称阻高)便逐渐得到国内外气象科技工作者们的广泛关注,这主要是由于阻塞高压的形成与维持可以引起区域乃至半球范围的大尺度气团动量和热量的强烈经向交换,导致大范围的天气气候异常,造成严重的气象灾害。因此,在全球气候变暖的背景下,对欧亚大陆关键区的阻塞高压进行深入研究,这对于揭示大气环流异常与极端天气气候事件频发之间的内在关系以及进一步提高中期天气预报准确率都具有重要的科学意义和现实意义。基于此,本文首先对现有的阻塞高压指数进行归纳总结,大致划分为四种。选取2008年初南方低温雨雪冰冻灾害期间的阻塞高压为个例,并结合国内外的研究,全面对比分析了这四种阻塞高压定量表征方法的优缺点。此后,在阻塞高压指数对比的基础上,选择能反映阻高动力学和热力学本质并且检索效果较好的阻高指数—PV—θ指数,对欧亚大陆影响我国天气气候较大的三个关键地区(乌拉尔山、贝加尔湖和鄂霍茨克海)阻塞高压进行了统计分析,进一步研究了阻塞高压与热带海洋地区ENSO,中高纬度PNA、NAO以及EA遥相关型等大尺度模态的关系。最后,着重研究了欧亚大陆三个关键地区阻塞高压对于我国冬季灾害性天气气候的影响,主要包括寒潮、低温雨雪冰冻、连阴雨和冬季干旱等。主要结论如下。1、归纳总结现有的客观定量表征阻塞高压的方法,大致可划分为：距平方法、T&M方法、PV-θ法和环流型法四种方法。以2008年初中国南方低温雨雪冰冻灾害期间阻塞高压事件为例,逐一分析了各种客观定量表征的阻塞高压方法的优、缺点,通过对比分析发现每一种方法都有其优缺点。相对而言,距平法和T&M方法简单易行：环流型法和PV-θ方法客观识别能力较强,应用前景较好。不管怎样,每种阻高客观检索方法作为一种可识别的方法都具有其可行性,研究者和业务部门可以针对具体情况选取适合的方法。比较而言,PV-θ阻高指数是对过去单纯利用高度和环流特征构造阻高指数的一种新的突破,其较强的客观识别能力能更好地满足实际应用的需求。2、利用PV-θ阻高指数对1950-2008年欧亚大陆三个关键地区阻高活动特征进行了统计分析。发现,这三个关键地区中乌拉尔山的年均阻塞频次是较高的,贝加尔湖和鄂霍茨克海地区的则相对较低。总体上,在乌拉尔山地区,年均阻塞频次在冬春夏季节较多而在秋季较少：贝加尔湖地区阻塞年均频次在冬夏秋季较多,春季较少；鄂霍茨克海年均阻高频次在冬夏季较多,而春秋季节较少；另外,夏季欧亚大陆地区年均阻塞频次在乌拉尔山和鄂霍茨克海地区有非常明显的双阻特征。在全球变暖的背景下,1950～2008年,乌拉尔山和贝加尔湖地区的阻高次数和天数有明显的线性增加趋势,而鄂霍茨克海地区,阻高活动也都有线性增加趋势,但并不显著。利用Morlet小波对影响我国天气的三个关键区的阻高活动进行了周期性分析,显示近59年来,乌拉尔山阻高活动主要存在2a和4a的显著性周期：贝加尔湖地区的阻高次数周期性主要体现在1970s到1980s存在的4～5年的显著性周期,鄂霍茨克海地区主要是阻高次数在1970s中期-1990s中期存在6-8a的显著性周期。3、ENSO对于欧亚大陆三个关键地区阻高活动有直接或间接影响。在El Nino年冬季,欧亚大陆三个关键地区阻高活动被抑制,而在La Nina年三个地区的阻高活动则得到加强：夏季处于发展时期的La Nina年,ENSO活动对于鄂霍茨克海地区的阻高活动有加强作用,相比较而言,处于发展时期的El Nino、处于衰退时期的El Nino和La Nina年夏季,ENSO活动对于三个关键地区阻高的影响都不显著。4、NAO、EA和PNA型遥相关对于欧亚大陆三个关键地区阻高活动有直接或间接影响。冬(春)季弱NAO有利于乌拉尔山(乌拉尔山和贝加尔湖)阻高形成；夏秋季节NAO对三个关键地区阻高影响较小。冬季强EA不利于三个地区阻塞的形成；在秋季,弱的EA有利于乌拉尔山到贝加尔湖西部地区阻塞高压的形成；春夏季节,EA对于三个关键地区影响不大。弱的PNA在冬季对乌拉尔山和贝加尔湖西部阻塞高压的形成有促进作用；秋季,强的PNA有利于乌拉尔山到贝加尔湖西部地区阻塞高压的形成；PNA在春夏季节对三个关键地区阻塞高压的影响不显著。5、研究欧亚大陆三个关键地区阻塞高压对于我国冬季灾害性天气(包括寒潮、低温雨雪冰冻,连阴雨以及冬季干旱)的影响,主要结论如下：阻塞高压对寒潮天气有重要影响,超过40%的寒潮天气是由阻高过程造成的,阻塞高压长时间维持的稳固形势以及高压北伸带来的北方冷空气对于我国寒潮天气的出现有着非常大的作用。阻塞高压的异常是造成2008年初南方低温雨雪冰冻灾害的重要原因,与1950-2008年的同期相比,2008年1月1日-2月2日期间三个关键地区阻塞高压主要有以下几个方面的异常特征：(1)阻高发生日数上：乌拉尔山和贝加尔湖阻高发生日数显著偏多,而鄂霍茨克海地区阻高日数比平均值略微偏少；(2)阻高强度上：乌拉尔山阻塞高压的强度偏强,贝加尔湖和鄂霍茨克海地区阻塞高压的强度则偏弱；(3)阻高发生位置上：乌拉尔山地区最大PV-θ指数发生位置偏东,而贝加尔湖地区最大PV-θ指数发生位置偏西,这种位置的配置说明此次灾害天气过程期间欧亚大陆关键地区阻塞高压在位置上很集中。对1月10日-2月2日南方连阴雨有作用的阻塞高压主要集中在乌拉尔山和贝加尔湖西部地区,阻高对于连阴雨的作用主要有两个方面,长时间维持使得分裂出的小槽活动偏多造成冷空气活动频繁,以及强大阻塞高压的维持使得冷空气不断南下补给。分析了阻塞高压对我国冬季干旱所起到的作用,发现在处于干旱事件的冬季,乌拉尔山西部地区容易有阻塞高压的产生；而在没有干早事件发生的冬季,贝加尔湖地区容易有阻塞高压的产生。统计发现,关键地区阻高与冬季干旱的发生有一定的对应关系。研究结果同时也说明影响我国冬季干旱因素很复杂,大气、海洋、青藏高原大地形等因素可能会共同影响我国冬季灾害性干旱气候事件的发生。更多还原

【Abstract】 Since 1940s, blocking highs have attracted much attention from meteorologists. Blocking high persists in the westerly in mid-high latitudes as a large-scale circumfluent system, its onset and decay are often accompanied with big circumfluent adjustment, even in the large hemisphere scale, resulting in widely abnormal weather and climate. Thus, under the global warming condition, it is practical and scientific to study blocking high, not even for a cogitation of inherent connection between abnormal general circulation and frequent extreme weather and climate events, but also for a better medium-range weather forecasting. Because of this background, in this paper, most of the existing blocking indices have been classified into four types, and then a comparison and analysis of these four objective methods are studied, by studying the blocking highs associated with the weather disaster in early 2008 over China for instance and combining related international studies. Based on the comparison, as its nature with dynamics and thermodynamics and ability to search blockings, the PV-θblocking index is chosen to study blocking highs in the Eurasia, as well as the relationship between blocking highs in the Eurasia and the ENSO, NAO, EA and PNA.Especially, the influence of the blocking highs in the three key regions of the Eurasia on the winter meteorological disasters is studied in China, including cold waves, the cryogenic freezing rain and snow weather, consecutive rain, and drought.The main results are as follows:(1) Existing blocking indices have been classified into four:the departure method, the T&M method, the PV-θindex, and the circumfluent type method. Using the blocking highs associated with the weather disaster in early 2008 over China for instance, a comparison and analysis of these four objective methods are studied. Results show that every method has its own merits and flaws. Comparatively, the departure method and the T&M method are easy to use and the PV-θindex and the circumfluent type method may have a better ability to define blocking episodes. Totally, every method for identifying blocking provided here can be used feasibly by operational departments and can be chosen to be compatible according to their need. However, the PV-θindex represents a new breakthrough for blocking indices which have previously used only geopotential height and/or the character of circulation. Furthermore, the ability of PV-θindex to quantify the occurrence of blocking could also satisfy the need for applying a consistent definition.(2) The PV-θblocking index is used to search the blocking highs of the Eurasia during 1950-2008. The results are shown as follows:the annual blocking frequency of the Ural is more than in the Baikal and the Okhotsk in the three regions of the Eurasia. The seasonal variations of the blocking highs of the three regions are different from each other. In the Ural, the annual blocking frequency is more in the winter, spring and summer than in the autumn; In the Baikal, the annual blocking frequency is more in autumn, summer and winter and less in spring. In the Okhotsk, the annual blocking frequency is more in summer and winter and less in spring and autumn. In the background of global warming, during 1950～2008, the blocking frequency/days increase linearly and significantly in Ural and Baikal, the trend of the blocking frequency/days in the Okhotsk is also ascending, but not so significant. The period analysis by using Morlet wavelet method shows that in recent 59 years, there are periods of 2a and 4a for the blocking activity in the Ural. The blocking frequency changes with period of 4～5a in the Baikal and 6～8a in the Okhotsk.(3) The blocking highs in the three key regions of the Eurasia are dominated by the ocean-atmosphere variability associated with ENSO directly or indirectly. Blockings in the three key regions are suppressed (enhanced) during the winter of EN (LN) years; in summer, LN during the developing stage can enhance blockings in Okhotsk. Relatively speaking, the influence of ENSO on the blockings in the three key regions is all unapparent during the developing EN year, the decaying EN and LN year. (4) The blocking highs in the three key regions of the Eurasia are related directly or indirectly to the NAO、EA and PNA. NAO in the negative phase could enhance the blockings in the Ural (the Ural and Baikal) in the winter (spring), but have less influence in the summer and autumn; with no significant influence as the NAO, EA in the negative phase could suppress the blockings in the three key regions in the winter, enhance the blockings in the Ural and eastern Baikal with negative phase in the autumn, and have less influence in the spring and summer; PNA could enhance the blockings in the Ural and Baikal with negative phase in the winter, enhance the blockings in the Ural and western Baikal with positive phase in the autumn, and have less influence in the spring and summer.(5) The influence of the blocking highs in the three key regions of the Eurasia on the winter disasters is studied in China, and the results show that, above 40% of the total cold waves were caused by blockings highs in the winter, indicating blocking highs have much influence on the cold waves, mainly by two aspects with the long time persistent steady posture and the cold air as the ridge extending to the north. As a important factors for the disaster with cryogenic freezing rain and snow weather in early 2008, blocking highs in the Eurasia are mainly abnormal in three aspects with more (appreciably less) blocking days in the Ural and Baikal (Okhotsk), stronger (weaker) blockings in the Ural (Baikal and Okhotsk), and concentrated blockings in the Ural and western Baikal, compared to the blocking activity during the same period from 1950 to 2008. Blocking highs in the Ural and western Baikal influenced the consecutive rain of south China during January 10th～February 2nd, mainly by long time persisting to bring more small trough and cold air supplied to the cold waves. The composite analysis shows, blocking highs is enhanced in the west of the Ural (Baikal) in winter with (without) arid disaster, statistical result of blockings in the Ural and Baikal also shows corresponding episodes to the drought in the winter, however result also indicates that the factors influencing the winter drought are very complex, maybe include atmosphere, ocean, Qinghai-Tibet Plateau and so on.更多还原