【作者】 潘婕；

【导师】 陶诗言； 纪立人；

【作者基本信息】 中国科学院研究生院（大气物理研究所） ， 气象学， 2007， 博士

【摘要】 本文定义了一个适于描写夏季欧亚中高纬环流基本特征的流型指数,对夏季欧亚中高纬持续异常流型进行了界定,利用合成、相关、EOF、小波分析等方法,研究了这类典型持续异常流型的气候特征,了解其年际、年代际变化,分析其影响因子的特征和关键区,并用广义E-P通量(T-N通量)分析方法从Rossby波能量频散的角度研究欧亚中高纬持续流型的维持机理;在诊断分析的基础上,用数值试验检验此类典型持续异常环流与其影响因子的关联,寻求和确定有指示意义的前兆信号,探讨此类环流由春入夏的演变规律及其在月尺度上的可预报性。全文主要结论如下:1.本文在前人工作基础上定义了一个夏季欧亚中高纬500hPa流型指数,用以界定夏季欧亚中高纬E、C型两类典型持续环流,具有代表性、合理性和明确的天气学意义。2.流型指数实际分布频数与正态分布理论概率的差值呈现双峰特征,均值附近偏少,表征E、C型环流发生频数的相对高值则偏多。3.气候平均的夏季欧亚逐日环流型呈现明显的季内阶段性特征,经历着与西太副高北跳、我国夏季雨带北移类似的阶段性变化,集合数值模拟也再现了这种特征。相关与合成分析也显示,E、C持续流型与我国夏季降水异常存在密切关系。4.对于E、C型过程,其海温分布存在差异,在北大西洋和北太平洋尤为显著。集合数值模拟结果肯定了北大西洋是产生SSTA影响的一个关键区,它对于E(C)型持续环流的形成维持起主导作用,这类海温分布型的出现可能有先期信号的指示意义。对E、C型过程加热场的相关、合成分析也在上述两大洋区域得到相似的分布形势,可见两大洋的影响不可忽略。另外对前期北极海冰覆盖率的合成分析表明,E、C型过程的前期海冰覆盖率也有明显差异,尤其在白令海峡、鄂霍次克海、巴伦支海和格陵兰海,C型比E型覆盖率明显偏多。5.Rossby波频散是E、C型过程形成和维持的重要机制。构成夏季欧亚中高纬异常环流型的几个成员(或活动中心)的形成和维持是相互联系的,表征Rossby波传播的波作用通量,往往由一个活动中心指向下游另一个中心,通过波能量的频散,链接几个中心的发展和维持。Rossby波传播特征在不同时期以及E、C型之间存在显著差异,Rossby波能量的频散过程基本上与各阶段背景流决定的弱波导结构一致。6.数值模拟结果证实了E(C)型过程的前春海温异常分布型的物理意义,肯定了它们是形成、维持E(C)型的重要因子。北大西洋SSTA在其中起主导作用,而北太平洋SSTA的影响不足以成为E(C)型形成的直接主导因子。对于2周-月尺度的模拟和预报来说,初始场的作用同样是重要的。7.以月平均环流指数作为预报对象,在数值模拟个例中,具有高可预报性的个例所占比例不多,反映了中高纬度环流的预报具有更大的不确定性。但是,多数预报集合仍是具有指导意义的,其中一些个例的SSTA外强迫可给出显著信号,如北大西洋区域出现典型E(C)型海温异常情况下,此时月平均环流具有较高的潜在可预报性。强E、C型初始场的作用也能使预报集合结果偏向环流的正、负异常态(E、C型),因此同样具有参考价值。8.1959～2000年夏季欧亚中高纬环流有明显的年代际变化,1980年前后流型指数均值发生了年代际突变。冬季NAO指数和夏季流型指数在年代际尺度上关系甚为密切,它们的年际相关也存在着年代际变化。合成分析表明,NAO高指数与E型过程对应的春季SSTA分布形势极为相似。与E、C型环流对应的海温、极冰异常的分布特征和关键区,在中期-月及年代际不同时间尺度上也表现出了一致性。上述结果印证了下垫面强迫在夏季欧亚中高纬持续流型的形成和维持中的作用。更多还原

【Abstract】 Based on the NCEP/NCAR reanalysis data and so on, the persistent anomaly of summertime circulation over mid-high latitude of Eurasia is investigated. We define an index‘I’representing the primary character of the summertime circulation over Eurasian mid-high latitude, and identify the persistent anomaly of summertime circulation over mid-high latitude of Eurasia. With method of composite, correlation, EOF, wavelet, and so on, the climatic feature of these typical persistent anomalies of circulation are discussed, their annual and decadal variation are analyzed, and the character and key area of the influencing factors are explored. The maintenance mechanism of these persistent anomalies is addressed in terms of a wave-activity flux and the westerly waveguide structure. Based on the diagnoses, we verify the connection existing between these persistent anomalies and the factor influencing them, seek the precursory signal for these anomalies, and reveal the evolution and the predictability at monthly time-scale of these circulations. The main result are as follows:1. An index‘I’to describe Eurasian mid-high latitudes circulation in summer is proposed, with it two kinds of typical persistent circulation patterns, i.e. type E and C, can be well identified. The index proves representative, rational and bears clear synoptic significance.2. The deviation of the observed frequence of‘I’from the normal distribution of probability shows a bimodal feature, i.e., the prior is smaller than the latter about the mean value and larger at the big absolute value which features the relative high frequency of occurrence for type E and C.3. Based on the daily circulation in summer, index averaged for 1959-2000 presents an obvious intraseasonal variation in stages in resemblance to the northward advance of the subtropical high over the West Pacific and summertime rain belt in China. Evidence shows that there is close relation between these anomalies of circulations and summertime rainfall anomalies in China.4. There is clear contrast between the SSTA of type E and C, especially over the North Atlantic and the North Pacific. The distribution of heat field corresponding to type E and C is similar to SSTA over above oceans. So, the influence on type E(C) of the two oceans can not be ignored. The Arctic sea ice in winter prior to type E(C) have obvious contrast too.5. For these typical anomalies of circulation, the Rossby wave dispersion is primary maintainance mechnism. The wave activity flux usually point from a centre of action to the next. The development and maiteance of these centres are linked by Rossby wave energy dispersion. The characteristics of Rossby wave propagation, however, is significantly different between type E and C and in the different periods of summertime.6. Numerical simulation confirm the physical meaning of the distribution of SSTA in spring corresponding to type E and C. The North Atlantic is a key area where SSTA plays a primary role for the formation and maintenance of type E and C, while the influence of North Pacific SSTA has no direct positive contribution to type E and C. For the simulation and forecast in the time scale of two weeks-month, the role of initial states are important too.7. Investigation of potential predictability in terms of the monthly average circulation index shows only a small portion of the cases studied are highly predictable, which reflects the prediction being subject to more uncertainties for mid-high latitudes circulation. However, the greater portion of emsemble forecast remain with some indicative meaning. For those cases where SSTA can give the significant signal, such as the typical SSTA over the North Atlantic corresponding to type E(C), there would be higher potential predictability.8. From 1959 to 2000, the summertime circulation over Eurasian mid-high latitude experienced obvious interdecadal variation that there presented a shift of the average index around 1980. The NAO index(in winter) and the circulation pattern index(in summer) show a similar trend for interannual and interdecadal variation. Highly statistic significant positive correlativity exist between the two index in interdecadal time-scale.更多还原