【作者】 宗海锋；

【导师】 张庆云； 陈烈庭；

【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】 本文根据中国730站旬降水资料和NCEP/NCAR日平均和月平均再分析资料,美国国家海洋大气局扩展重建月平均海表温度资料。采用SVD、相关分析、合成分析、线性回归分析以及扩展SVD(ESVD)等方法分析了梅雨期降水与前期冬季海温、同期大气环流之间的关系,重点探讨了冬季ENSO导致梅雨期东亚-太平洋(EAP)遥相关型的形成过程,以及ENSO引起的全球和局地大气环流和海温异常在梅雨期EAP遥相关型形成中的作用,并用IAP-9L-AGCM大气环流模式进行了数值模拟试验。主要结论如下:1)梅雨期降水与前期冬季海温的SVD分析表明,长江流域梅雨期降水不仅与赤道中东太平洋海温密切相关,而且还与ENSO锁定的赤道印度洋、黑潮区、暖池区、亲潮区等海区的海温有密切联系。长江流域梅雨期降水异常是对ENSO盛期整体海温异常型长时间响应的结果。2)梅雨期降水与同期500hPa位势高度场的SVD分析表明,长江流域梅雨期降水与东亚-太平洋地区由西太平洋副热带高压、梅雨槽和鄂霍次克海高压所构成的EAP遥相关型密切相关,是EAP遥相关型的直接表现。并强调了这3个环流系统作为一个整体对长江流域梅雨期降水异常作用的重要性。3)冬季海温场与12～6月500hPa位势高度场的ESVD分析发现,从12月到次年6月500hPa高度层上在热带地区整个印度洋-太平洋范围高度始终偏高,西太平洋副热带高压一直偏强,而中高纬度地区的环流也有相当的持续性和一定的变化规律。到了4～5月东亚-西太平洋地区从低纬到高纬正、负、正的相关分布型基本形成。因此指出与长江流域梅雨期降水密切相关的EAP遥相关型是对ENSO盛期海温型响应的结果。4)揭示了联系冬季ENSO和梅雨期EAP遥相关型的3个主要关键过程:(a)西北太平洋低纬地区反气旋异常环流的形成和维持,使初夏副热带高压偏南加强。(b)东亚大槽持续偏弱,冷空气活动路径偏北偏东,有利于西北太平洋海温呈亲潮海区冷,黑潮海区暖的海温距平分布。这一分布对EAP遥相关型的形成有极重要的作用。(c)PNA遥相关型的持续发展,使极区位势高度明显增加,为鄂霍次克海高压的形成提供了有利的背景条件。5)SVD和ESVD分析结果中时间系数的演变表明:ENSO盛期海温型、长江流域梅雨期降水以及EAP遥相关型3者之间,不仅年际变化关系密切,而且在1970年代末都出现了由负值期向正值期的突变现象。6)El Nino年和La Nina年全球冬季1000～500hPa厚度标准化距平分析表明:El Nino盛期不仅印度洋和太平洋上空对流层低层平均温度偏高,而且是全球热带地区对流层低层的平均温度都偏高,幅度达1.0～1.5标准差。而南、北半球中高纬大部分地区气温偏低,幅度达-0.5～-1.0标准差。La Nina盛期的情况相似,但符号完全相反。这进一步证实了ENSO影响的全球性。由于热带地区的1000～500hPa厚度距平与南、北半球中高纬地区存在反号的关系。El Nino位相,南、北半球的经向温度梯度增强,有利于全球纬向环流的发展,La Nina位相,有利于经向环流的发展。7)1961～2000年北半球(Inorth)、南半球(Isouth)和全球(Iglobal)500hPa环流指数的分析发现,它们的演变与Nino3区SST的非常一致,相关系数Inorth为0.82、Isouth为0.90、Iglobal为0.82,均超过99.9%的信度水平。说明无论是南、北半球或全球范围的500hPa环流指数都存在周期为3~5年的循环变化。8)这一ENSO强迫引起的3~5年的环流指数循环与大气内部的动力学所引发的几周的高、低指数循环不同,是全球性的,并具有一定的流型。就亚太地区而言,在El Nino位相,东亚大槽减弱,热带西太平洋为反气旋性异常环流控制;东太平洋-北美地区PNA遥相关型发展。在La Nina位相情况相反。因此,El Nino强迫引起的环流型为梅雨期EAP遥相关型的形成提供了非常重要的背景条件。9)ENSO衰减期大气环流和海温异常持续性的分析表明:El Nino衰减年和La Nina衰减年大气环流和海温的持续性都比非ENSO年要大的多。由此指出ENSO海温异常型及由ENSO海温异常型导致大气环流异常型之间存在强的耦合关系,使得海温及大气环流随时间演变极为缓慢。进而导致在ENSO衰减年大气环流及海温有很强的持续性。而一般年份海温和大气环流的持续性差。10)ENSO衰减期西北太平洋地区局地海气相互作用分析发现,局地海气相互耦合相互影响,导致从El Nino衰减年冬季直到初夏暖池区、黑潮区、亲潮区维持着负、正、负海温距平分布型,而这种负、正、负的海温距平分布型通过局地海气相互作用最终导致了初夏东亚地区EAP流型的形成。11)数值试验结果成功的模拟出了ENSO衰减年EAP遥相关型以及PNA型的出现,此外数值模拟成功的模拟出了El Nino衰减年和La Nina年衰减年初夏我国东部地区的降水的异常分布,进一步证实了初夏EAP遥相关型出现和长江流域梅雨期降水异常是东亚地区大气环流对ENSO异常海温型遥强迫长期响应的结果。12)在文章最后我们提出了一个关于ENSO影响梅雨期降水的可能机制。更多还原

【Abstract】 The relations between the Meiyu rainfall (MYR) and pre-winter sea surface temperature (SST) and relations between MYR and circulation during the Meiyu period are studied by using singular value decomposition (SVD), extend singular value decomposition (ESVD), correlation, composition and linear regression methods with 730 China stations ten-days mean rainfall, NCEP/NCAR daily and monthly mean reanalysis data, extended reconstruct sea surface temperature (ERSST). The formation processes of EAP during the Meiyu period caused by ENSO are discussed. And the actions of global and regional circulation anomalies aroused by ENSO are studied too. In the end we carried some numerical experiments to model the formation of EAP teleconnection by using IAP 9L AGCM. Main conclusions are as follows:1) The SVD results of the MYR and pre-winter SST show: the MYR over the Yangtze River reaches not only has tight relation to the middle and east equatorial Pacific SST, but to other regions SST locked with ENSO such as equatorial Indian Ocean, warm pool, Kuroshio extent, oyashio extent et al.. The MYR anomalies are results long corresponding to the abnormal SST patterns during the ENSO mature phase.2) The SVD results of the MYR and homochronous circulation show: the MYR has tight relation to the EAP teleconnection formed by west pacific subtropical high, the Meiyu trough and the Okhotsk high. It is the three circulation systems work wholly that leads to the MYR anomalies.3) The ESVD results of the prewinter SST and December to June Geopotential height at 500 hPa level show: from December to June the height is above normal over the tropical Indian Ocean and Pacific, which resulting in the west subtropical high stronger than normal. And the atmosphere circulation over middle and high latitude also has considerable continuities, and transforms in some manners. During April and May the correlation pattern: positive in low latitude, negative in middle latitude and positive in high latitude correlation has come into being by and large over the eastern Asia and west pacific. These results furtherly confirm that the EAP teleconnection which has tight relation to the MYR over the Yangtze River is the results corresponding to the abnormal SST patterns during the ENSO mature phase too. 4) Via the ESVD anaylisis, we put forward that there are three key processes linking prewinter ENSO to the EAP teleconnection during the Meiyu Period. These key processed are as follows:(a) The anti cyclone’s forming and maintaining leads to the west Pacific subtropical high more southward and stronger than normal.(b)The East Asia trough keeps continually weaker than normal, which favors the cold air moving path more eastward and northward. Such circulation benefits Oyashio SST lower and Kuroshio SST higher. And such SST anomalies distribution over the west Pacific is very important to the formation of EAP teleconnection during the Meiyu period. (c)The continual development of PNA teleconnection causes the height to increase over Arctic regions, which offers a favored background for the formation of Okhotsk high.5) The evolvement of time series in SVD and ESVD results show that the MYR, EAP teleconnection and SST anomalies Pattern in prewinter are not only consistent in interannual scale, but in interdecadal scales. They all experience a change from negative period to positive period in the end of 1970’s.6) The analysis of the anomalies of global winter 1000-500hPa thickness for El Nino and La Nina year respectively shows that during the El Nino mature phase, the mean temperature increases in low troposphere over the global tropical regions, not just located over Indian Ocean and Pacific, increasing amplitude about 1.0~1.5 standardized deviations. At the same time the temperature decreases in the middle and high latitude regions of both hemispheres, decreasing amplitude about -0.5~1.0 standardized deviations, the 1000-500 hPa thickness anomalies over the tropical regions are opposite to the anomalies over middle and high latitude in sign. Results for La Nina are similar to El Nino, but the sign is in reverse to El Nino. This further confirms that the global influence of ENSO. For El Nino phase the longitudinal gradient of Temperature’s is enlarged, which is favorable for the zonal circulation development. On the contrary, the situation is favorable for longitudinal circulation development in La Nina phase.7) The evolvement of 500 hPa circulation indexes for global, north hemisphere and south hemisphere from 1961-2000 shows that they are all consistent with SST over Nino3 area. The correlation coefficients between these indexes and Nino3 SST are 0.82(Global), 0.90 (South hemisphere) and 0.82 (North hemisphere), all above the 99.9% confident level. It shows that all 500 hPa circulation indexes (Global, South hemisphere and North hemisphere) vary in a cycle about 3~5 years.8) The 3~5 years circulation index cycle forced by ENSO is different with the high and low index cycle in period about some weeks caused by the internal dynamics of the atmosphere. Because the 3~5 years circulation index cycle represents certain circulation styles at the same time. As for the Asia-Pacific region, the East Asia is weaker, an anticyclone hovers over the West tropical Pacific, and the PNA teleconnection develops over East Pacific-North America in El Nino phase; and opposite in La Nina phase. So the circulation forced by El Nino offers a very important background for the formation of EAP teleconnection during the Meiyu period.9) The analysis of continuities of circulation and SST during ENSO decaying year shows that the continuities of circulation and SST are greater in ENSO decaying years than in normal years. Further studies show that the greater continuities of circulation and SST are due to the stronger coupling relations between circulation and SST in ENSO decaying years, which slows down the evolvement speed of circulation and SST , leading to stronger continuities of circulation and SST in ENSO decaying years than in normal year.10) The study about regional air-sea action over north west Pacific shows that the coupling and influencing on each other between air and sea, leads to SST lower over warmpool, higher over Kuroshio and lower over Oyashio, presenting a anomalies feature that negative over warmpool, positive over Kuroshio and negative over Oyashio from winter to early summer in El Nino decaying year. This SST anomalies distribution forming and continuing over West Pacific leads to the formation of EAP teleconnection in early summer.11) The numerical experiment succeed in modeling the formation of EAP teleconnection and PNA teleconnection in early summer, and the numerical experiment also succeed in modeling the precipitation anomlies over east China in early summer of ENSO decaying year. These results furtherly prove that the EAP teleconnection and precipitation anomlies ove the Yangtze River valleys are response of atmosphere circulation over East Asia to ENSO SST anomlies remote forcing in long time period.12) A possible mechanism about the influence of ENSO on the MYR is brought forward in the end of this paper.更多还原