【作者】 梁苏洁；

【导师】 丁一汇； 赵南；

【作者基本信息】 中国气象科学研究院 ， 气象学， 2014， 博士

【摘要】 IPCC第五次评估报告指出，全球平均气温自1998年以来并没有呈现显著上升（基本趋平），即进入所谓全球变暖趋缓或停顿时期，并且这种变化还有可能持续一段时间。在这一背景下，重新对我国气温及其相关的区域环流的年代际变化特征进行研究是具有科学和实际意义的，有助于深入理解全球气候变化对区域温度和环流影响的过程和机制。本文的研究主要得到下列结论：（1）对中国大陆1960~2013年53个冬季气温的年代际变化特征进行分析和气候跃变检验发现，中国冬季气温在整体变暖的趋势上叠加有年代际波动，可划分为冷期、暖期和停滞期三个时期。并据此对比分析三个阶段内东亚大气环流和东亚冬季风强度的差异，结果表明，伴随着气温的冷-暖-冷变化，东亚冬季风的强度也出现了强-弱-强的变化。并且东亚高空急流、东亚大槽和西伯利亚高压也出现了类似的年代际变化。在上述研究的基础上，将PDO的年代际变化分量作为背景，分析NAM/AO和ENSO不同配置下对中国冬季气温和东亚冬季风环流的影响，结果发现，PDO和ENSO这两种海洋表层温度变率模态与NAM/AO的不同配置，对中国冬季气温和冬季风以及极端低温事件有不同的影响。它们不仅影响中国冬季气温一致型（EOF1）的年代际变化，而且也可以影响到冬季气温南北反相分布型（EOF2）的变化，这从自然原因方面解释了1980s和1990s中国快速变暖与最近十年北方降温趋势较为明显的观测事实。研究也指出当PDO为负位相时，NAM/AO也常出现负位相。（2）本文进一步揭示了NAM/AO直接影响我国冬季气温的两种方式。对此着重分析了NAM/AO指数异常事件中北极冷空气活动的优势路径及其对中国冬季气温的影响途径和方式。研究结果表明，在正NAM/AO指数异常事件中，北极地区近地面冷空气大多被局限在中高纬地区，极区为气旋式运动。极区冷空气较少地影响到我国北方地区，气温偏高。但在指数下降过程中，东欧槽和南支槽加深，这有利于欧洲中高纬冷空气向东侵入中国，同时也利于孟加拉湾水汽向中国华南地区输送，为造成大范围寒潮天气甚至冰冻雨雪天气提供了有利条件。第二种影响方式，是发生在NAM/AO为负指数异常时期，这种情况下极区存在反气旋式运动，同时中纬度地区的经向环流型加强，并且在指数下降阶段出现了强烈影响欧亚大陆的冷空气活动路径，冷空气团可以直接进入我国东北部地区，造成东北地区大范围的寒潮暴雪等剧烈天气，同时可进一步向南传播造成我国东部地区的大范围降温。（3）在上述大尺度环流背景下，本文分析和讨论了不同类型的强区域持续性极端低温事件的发生频率和路径。结果表明，我国的强区域持续性极端低温事件在冷期多发且强度更强，而暖期较少强度减弱，停滞期爆发频率增加。尤其是在NAM/AO负指数时期，东北型极端低温事件的爆发频率和强度增加。（4）本文还用6个CMIP5模式评估和预估了中国冬季气温变化。模拟的结果表明，模式大多基本能模拟出冷暖时期的突变时间，并且中国区域冬季气温一致型（EOF1）增暖的变化趋势模拟较好。模式结果也可以大体反映出南北反向型（EOF2）的时空变化。但在冷暖期的突变时间点以及两个模态的模拟上，BCC-CSM-1.1模式模拟的结果与实际观测相比较其他模式更为符合。在高、中、低三种排放情景下的模式预测结果表明，未来中国区域的冬季气温仍呈现上升趋势，并叠加有年代际变化，其中停滞期大致在2010~2025年期间结束，之后中国冬季气温继续加速上升。更多还原

【Abstract】 The IPCC’s Fifth Assessment Report claims that the global mean surface air temperature hasremained flat for the past15years, termed the global warming hiatus period. And some research resultssuggest that there is a chance that the current observed hiatus could extend for several more years. Undermentioned backgrounds, analyzing the interdecadal changes of the surface air temperature (SAT) overChina mainland anew is a potential scientific value and practical significance. Considering that thewintertime SAT is characterized by the significant interdecadal time scale, the study on which will deepthe present understanding of the global warming and promote the predictability of the future SAT. Theconclusions are derived as follows:(1) Based on the daily air surface temperature data of468meteorological observation stations inthe mainland of China from1960~2013, the spatial and temporal characteristics of winter temperatureare analyzed. Firstly, the linear regression and regime shift detection methods are used to identify thetendency and abrupt point. The result is that the winter temperature shows an interdecadal variabilitysuperimposed on the long-term warming trend, with the cold period in1960/61~1985/86, the warmperiod in1986/87~2005/06and the hiatus period in2006/07~2012/13. To understand the underlyingmechanism for the formation of the three periods, the atmospheric circulation systems are compared byusing the NCEP/NCAR reanalysis data. It is found that the cold/hiatus (warm) period is characterizedby weak (strong) zonal wind in the middle and high latitude of the Northern Hemisphere, strong (weak)East Asian Trough on500hPa geopotential height field, strong (weak) downdraft after the trough, strong (weak) Siberian High and enhanced (weakened) northeast surface wind over Asian continent.These provide favorable circulation conditions for cold (warm) winter in the mainland of China.Furthermore, by influencing the East Asian winter monsoon circulations the Northern HemisphereAnnular Mode (NAM)/Arctic Oscillation (AO) puts an impact on the winter temperature, especially thewinter minimum temperature on the interdecadal timescale.On the other hand, the Pacific Decadal Oscillation (PDO) is positively correlated to the wintertemperature on the interdecadal timescale. Subsequently, the results indicate that with the modulation ofthe interdecadal variability of the PDO the combined effects of the NAM/AO and ENSO not onlyinfluence the first EOF1mode that has an identical signal in whole China, but also influence the secondEOF mode that has a seesaw pattern between southern and northern China. In addition, thesuperimposition of EOF1and EOF2probably causes persistent warming winters in the1980s and1990s and may be responsible for the significant cooling trend during the last seven years in NorthwestChina and Northeast China. The results also point out that the NAM/AO tends to be at negative phaseduring negative phase of the PDO.(2) The paper confirms that the NAM/AO is an important factor affecting winter SAT over China.This is because that on the synoptic time scale the NAM/AO has an influence on the movement of thenear surface cold air in the Arctic, which is very important in the outbreak of the cold wave. The paperfocuses on analyzing the superior trajectory of the near surface cold air in the Arctic during the abnormalNAM/AO index events and how these cold airs can affect the SAT over China. The results show thatduring the positive NAM/AO index event, the near surface air is restricted in the Arctic and high latitudeareas, characterized by cyclonical trajectory. In this case, the Arctic cold air seldom sweeps down overnorth China so that the winter SAT is warmer than normal. During the NAM/AO index descentingphase, the circulation pattern is beneficial to intrusions of the cold air from mid-high latitudes of Europeto southern China and transporting of the water vapor from the Bay of Bengal to South China with the East European Trough and the southern branch trough deepening, which provide favorable atmosphericconditions for the low temperature weather, for example the cold wave or even snow calamity. On thecontrary, during the negative NAM/AO index event, the near surface air flows out the Arctic in theanticyclonical trajectory. At the same time, the meridional circulation pattern is intensified in themid-high latitudes. During the NAM/AO index descenting phase, the cold air can directly affect thenortheast part of China and the Mongolia Cold Wave key area. The latter cooperates with otheratmospheric circulation systems can induce cold waves in the eastern China.(3) However, the NAM/AO is not the single factor that modulating the outbreak of cold wave andother low temperature weather that are subject to many other circulation patterns. The paper analyzesthe different patterns of the strong regional prolonged low temperature events (RPLTE) in China. Theresults show the frequency and intensity of the RPLTE is higher and stronger in the cold period, whilethe frequency and intensity is lower and weaker in the warm period. So far the frequency of the RPLTEis increasing during the hiatus period. In general the NAM/AO index is negative during early andmature stage of the Northeastern type and the Eastern type of the RPLTE, while the relationshipbetween the other types of the RPLTE and the NAM/AO index is uncertain.(4) The simulated capability of6global system modes released by Coupled ModelIntercomparison Project Phase5(CMIP5) is tested for the wintertime SAT over China. The6modelscan reasonably reproduce the evolution of wintertime SAT over China during the1960~2005incapturing the long term trend of warming especially in the North China. Also, the6models can almostcapture the spatiotemporal structures of the second EOF mode that has a seesaw pattern betweensouthern and northern China. The models of BCC-CSM1.1can detect the regime shift in the EOF1corresponding normalized time coefficient of the wintertime SAT over China.6model scenarioprojections of future climate change during2006~2035indicate that the wintertime SAT over Chinawould continue to rise, while the intensities are scenario-dependent. The results indicate that the wintertemperature shows an interdecadal variability superimposed on the long-term warming trend, with thehiatus period ending around2010~2025. After that the wintertime SAT over China will increase warming.更多还原