【作者】 马丽萍；

【导师】 陈联寿；

【作者基本信息】 南京信息工程大学 ， 气象学， 2009， 博士

【摘要】 台风活动与全球气候变暖之间的关系是当前台风＼飓风气候学的研究热点。本文首先主要系统地研究了全球气候变暖对西北太平洋和东太平洋热带气旋（TC）频数的影响。针对若干TC形成的必要条件在响应全球变暖时的产生的气候变化,来寻找引起TC频数气候变化的可能原因,重点放在以下三个热力学及动力学因子气候变化特征,旨在揭示全球变暖的背景下台风活动的长期变化趋势及其可能的热力、动力学机理。其次,利用TC最大潜在强度理论（Maximum Potential Intensity,MPI）研究了20世纪和全球进一步变暖的背景下西北太平洋TC MPI的变化趋势。主要研究结果如下:首先,研究过去60（1949-2008）年热带北太平洋TC生成的主要初始起源地-大尺度ITCZ（Intertropical Convergence Zone）的气候变率,利用NCEP再分析资料的分析研究发现,依照信风辐合类型和地理位置,北太平洋ITCZ清楚地分成三段,即1)位于西北太平洋100-140°E,10-20°N附近的季风辐合带（简称ITCZ-Ⅰ）;2)位于140°E-140。W,5-15°N附近北太平洋中部的ITCZ（简称ITCZ-Ⅱ）;3)位于东太平洋140°W-90°W,10-18°N附近的ITCZ（简称ITCZ-Ⅲ）。研究结果表明,过去60年ITCZ的空间分布和气候变率存在区域特征----其强度呈现出西减东增、位置呈现出西落东抬的气候变率。其次,对TC生成的另一必要条件-垂直切变的气候变率进行了研究,基于NCEP再分析资料,过去60年热带北太平洋的垂直切变（200-850hPa差）空间分布以及气候变率在不同海区存在区域差异,联系区域TC发生频数和垂直切变气候分布的特征,把TC活动关键区的垂直切变分成三个关键区,1)位于西北太平洋100-140°E,5-20°N区域的东风垂直切变减小;位于西北太平洋140-180E,10-25°N范围西风垂直切变增加;位于东太平洋130°W-90°W,7-18°N区域东风切变表现增加趋势。最后,根据NCEP再分析资料研究过去60年热带北太平洋增暖过程,发现原来局限在太平洋西部跨赤道的高海温或称作暖池的28℃以上的闭合区域逐年代向中东太平洋扩展,最后20年热带东西太平洋连接起成一条完整的连续的高海温带。太平洋中部和东部的海面增暖后存在明显的南北向SST梯度。根据本文的分析研究,SST增暖的不均匀性可能是造成北太平洋ITCZ区域差异的原因之一。在模式资料研究方面,利用IPCC（Intergovernmental Panel on Climate Change）WCRP WGCM CMIP3（World Climate Research Programmers’s Coupled ModelIntercomparison Project 3）高分辨率全球耦合多模式资料集（Multi-Model Dataset）研究TC生成的上述三个条件响应气候变暖背景下的气候变率以及变化趋势,其结果与NCEP再分析资料得到的诊断结论基本吻合。观测事实表明,无论是西北太平洋（180°E）还是140°E以西海域,近40年来热带气旋频数在明显减少。本文的研究结果表明,这一海域热带气旋频数减少的原因和西北太平洋热带辐合带ITCZ-Ⅰ强度减弱和向赤道一侧位移（Equatorialward displacement）有关。这一区域风速垂直切变在明显减小和SST增暖的变化趋势对这一海域热带气旋发生频数增多是有利的,但它并不能补偿ITCZ的不利作用而使TC频数增加。分析结果还表明,东北太平洋除了海面温度增暖和西北太平洋是一致的,都是全球增暖的一部分,但东太平洋风速垂直切变在增强,热带气旋发生频数在增加。这样的变化趋势与西北太平洋上的变化趋势恰恰相反,这一海域垂直切变的增加却未能抑制热带气旋的发生。而东北太平洋的热带辐合带即ITCZ-Ⅲ在加强并产生向极位移（Polarward displacement）,这样的变化也与西北太平洋完全相反。特别是ITCZ-Ⅲ强度增加的幅度很大,从1949-2008年其中心平均正相对涡度从开始的0.1^*10^-5s^-1一直增加到最后0.7^*10^-5s^-1,如此强的加强趋势可能是导致这个区域TC频数增加的主要原因之一,即使垂直切变增加也没有抑制TC频数的增加。但不论热带气旋是增多还是在减少,都与ITCZ强度和位移的有利变化一致。研究的结果还表明,西北太平洋热带气旋发生频数的年代际变化还与ENSO冷暖事件的更迭有关。本文分析表明,50年代至70年代末之前,ENSO冷事件发生强而频繁。70年代末以后,ENSO暖事件发生强而频繁,这与IPCC第三次评估报告发表的结果也是一致的。ENSO冷事件占优势的年代,西北太平洋热带气旋发生频数高,反之,ENSO暖事件发生占优势的年代,西北太平洋热带气旋发生频数低。春季MEI指数与西北太平洋热带气旋频数存在很好的反相关关系,特别是4月/5月的相关关系最好,相关系数为-0.5。在研究TC强度响应全球变暖发生的变化趋势时,由于TC强度的历史观测资料的不可靠性,观测事实无法判断TC强度的气候变化趋势。因此本文重点研究在全球气候变暖下,西北太平洋热带气旋的最大潜在强度（Tropical CycloneMaximum Potential Intensity,以下简称TC MPI）的变化趋势。利用IPCC WCRPCMIP3全球耦合多模式资料集,评估全球气候变暖下,TC MPI的变化趋势。多模式集成结果表明:在20世纪气候背景下,最后40年SST和对流层上层气温增暖不显著,西北太平洋热带气旋的最大潜在强度呈现出年代际及多年代际振荡。在20世纪多模式中,没有自然强迫而只有温室气体强迫的模式表现SST增暖更明显的特点,而自然因子强迫和温室气体共同强迫的模式对流层上层和海表面增暖较小,自然强迫因子抑制了对流层上层气温和海面温度的进一步增暖。在CO2浓度每年以1%增长率增加的气候背景下,TC MPI随着SST和对流层上层气温显著增暖而同步增加。同时也发现TC MPI的振幅与对流层上层气温振幅反相关。变暖后的气候背景下最后40年、最后30年、最后20年相比较20世纪最后40年、最后30年、最后20年,西北太平洋TC MPI的持续最大风速增加5-10%。其他科学家的模式研究也认为全球变暖背景下TC MPI增强,这种关联不一定通过SST的升高,而是通过排放的CO2产生的温室效应造成。Hender-Sellers等（见第7章文献5）的估算表明,CO2加倍的情况下,台风的MPI将增加10-20%。更多还原

【Abstract】 The impact of global warming on tropical cyclone（TC） genesis frequency and TC intensity are investigated.We focus mainly on climate variability of the both thermodynamic and dynamic necessary conditions which influence TC formation in response to global warming.We also investigated the relationship between ENSO events interdecadal variability and TC frequency variability under the global warming. Finally,TC intensity variation responding to global warming is discussed in this study.The research results show as follows:Firstly,the intertropical convergence zone（ITCZ） strength interdecadal/multidecadal variability over the tropical NP is investigated based on the NCEP/NCAR reanalysis data.The results from this study show that the NP ITCZ can be divided into three sections according to its wind convergence types and geographical positions,namely the ITCZ section locating at 100-140°E,10-20°N named ITCZ-Ⅰ; the section locating at 140°E -140°W,5-15°N named ITCZ-Ⅱand the one in the eastern NP locating at 140°W-90°W,10-18°N named ITCZ-Ⅲ.ITCZ three sections demonstrate their different long-term variability respectively,namely the ITCZ-Ⅰweakened generally and both ITCZ-Ⅱand ITCZ-Ⅲstrengthened with some fluctuations in July-October（JASO）.Secondly,the zonal wind vertical shear long-term variation over the tropical NP is investigated.The results based on NCEP reanalysis show in the North Pacific,there are three key regions which display different characteristics in terms of TC formation and different wind shear.The results show that the variation of mean vertical shear locating at 100-140°E,5-20°become weakening,it is enhanced within 140-180°E,10-25°N area,and it strengthen in the basin of 130-90°W,7-18°N over the eastern Pacific during 1949-2008.Thirdly,sea surface temperature variation in tropical North Pacific（NP） is investigated based on the NCEP/NCAR reanalysis data It is found that the SST over the tropical Pacific are gradually increased during the past 60 years,suggesting that the warm pool has extended into central Pacific even into the equatorial eastern Pacific during the recent years if the definition of taking 28℃as the critical temperature for the warm pool is adopted.There produced obvious SST gradients in the central Pacific and east Pacific owing to inhomogeneous warming,a possible cause responsible for the heterogeneous variability in the ITCZ strength is suggested via differential SST gradients.We checked climate variability of these three TC formation factors based on coupled multi-model datasets in the World Climate Research Programmers’s Coupled Model Intercomparison Project 3（WCRP CMIP3） of Intergovernmental Panel on Climate Change（IPCC） with the increasing CO2 concentration 1%per year climate scenario.The simulation results are similarly with the results based on the NCEP reanalysis data.The results for concerning the climate variabilities of TC formation conditions have related relationship with TC genesis frequency.Such as,in the past 40 years,sea surface has warmed quickly and mean SST increase about 0.6℃in the WNP（west to 140°E）,while the frequency of TC under the background of global warming is decreases.The researches demonstrate that the following aspects may suppress the tropical cyclone formation and its frequency.（1） Vorticities within ITCZ locating at （10-20°N,100-140°E） is weakening;（2） The ITCZ and subtropical high ridge is shifting gradually equatorwards displacement.Both of the above causes are disadvantageous to tropical cyclone formation and development under the warming sea surface temperature background.However,TC frequency is increasing in the recent 40 years over EP basin,where ITCZ strength is strengthening remarkably and position is shifting polarward displacement which mainly possible causes are responsible for TC increase in this area though the zonal wind vertical shear enhancing at the same period dose not inhibit TC formation.In a summary,wherever,the TC formation is mainly detemined by the ITCZ strength and position,that is,when the ITCZ strength weaken and its position shifting eqautorward displacement,TC formation decrease even if other factors are favorable to TC formation,such as zonal wind vertical shear weakening and SST warming,which is the case in the WNP basin,while the ITCZ strength strengthen and its position equatorwards displacement,TC formation increase even if zonal wind vertical shear reinforce,which is the case in EP region.On the other hand,it is well known that the ENSO events have good relationship with TC genesis frequency.The research results reveal that ENSO events have obvious interdecadal variability during 1950-2007 based on the Multivariate ENSO Index（MEI）, in which cold ENSO events are stronger and more frequent during the beginning of 1950’s up to the late 1970’s,the TC genesis frequency is quite high,and from mid 1970’s up to now the warm ENSO events are and stronger more frequent under the global warming background which is the lower TC genesis frequency unanimously in this period.The spring MEI,especially that in Apr/May,has a good negative correlation with TC annual frequency with the correlation coefficient of-0.5 during 1950-2007.Fainally,as for how does global warming impact on TC intensity.The study reaches conclusions as follows:Firstly,the historical TC intensity observational data could not be used to determine its climate trend owing to the data quality issues with heterogeneity of technique for measuring and fixing the intensity.In this study,the impact of global warming on the theoretical maximum potential intensity（MPI） of tropical cyclones over the WNP is evaluated using the coupled multi-model datasets in the WCRP CMIP3 of IPCC.Our results show that there is no significant increasing trend in TC MPI responding to both SST and upper tropospheric temperature increasing slightly in the WPN for the 20^th century climate background,while considerable interdecadal fluctuations in MPI are found to be associated with the variation in the upper tropospheric temperature.In contrary,a consistent increasing trend in TC MPI is found over the whole basin owing to the increasing CO₂ concentration and SST.It is shown that with the doubled CO₂,the MPI measured in the sustained maximum near surface wind speed is increased by 5-10%in the WNP basin.Considerable fluctuations in MPI are again found and are inversely correlated with the fluctuations in the upper tropospheric temperature.更多还原