海温异常对东亚夏季风影响机理的研究进展

从短期气候预测关注的外强迫信号角度出发,回顾了国内外在海温异常对东亚夏季风和我国汛期降水影响机理方面的主要研究进展,重点评述了热带太平洋ENSO循环、热带印度洋全区一致型海温模态、热带印度洋海温异常偶极子、南印度洋偶极子和北大西洋海温三极子模态的年际变化及其对东亚夏季风年际变率的影响。从研究成果在短期气候预测业务中应用的角度,重点关注海温异常和东亚夏季风年际变率以及我国汛期降水多雨带位置的关系,总结了海温异常作为外强迫信号对我国汛期降水预测的指示意义以及汛期降水预测的难度。最后指出气候预测业务对东亚夏季风影响的机理研究和动力气候模式发展方面的需求。     

1999年与2003年我国北方地区夏季气温异常原因初探

分析了1999年与2003年我国北方地区夏季气温的变化特点和同期大气环流主要特征。结果表明:中国夏季气温变化有明显的年代际特征,这一特征与亚洲上空大气环流的年代际变化紧密相关,表明我国北方地区夏季气温异常一个很重要的原因或许是缘于气候年代际变化。2003年夏季中高纬环流形势呈两槽两脊的配置,与近十几年气候态分布刚好相反,因而从气候年代际变化的特征来看,2003年为预示年代际气候转型的征兆。     

全球海洋大气耦合环流模式中的ENSO特征对气候背景态改变的敏感性

文中利用一个高分辨率全球海-气耦合环流模式设计两组长期积分试验,揭示了在不同气候背景态下热带太平洋年际变化特征及模式ENSO循环控制机理的差异。通过分析海表温度、上层海洋热容量和低层风场异常的年际变化特征及其和赤道中东太平洋海表温度异常的关系,揭示了基于不同气候背景场的ENSO循环的不同演变过程。结果表明:ENSO年际变率特征(包括振幅、频率等)对气候背景态相当敏感,在不同的背景场下ENSO循环的控制模态可以明显不同。试验表明,当热带太平洋东冷西暖的背景热力梯度接近多年气候平均时,模式ENSO循环表现为所谓的“时滞振子”模态控制,而随着东西向背景热力梯度显著减小,ENSO循环则可以表现为驻波模态控制。研究结果为认识年代际背景变化影响年际ENSO循环的机理提供了一种启示。     

土壤湿度年际异常对中国春、夏季气候模拟的影响

基于NCAR大气模式CAM3.1模式,设计了有、无土壤湿度年际异常两组试验对中国区域近40a(1961-2000年)气候进行了模拟。从气候态和年际变率的角度,通过分析两组试验的差值场来探讨土壤湿度年际异常对气候模拟的影响,并初步探讨了影响的可能机制。结果表明:模式模拟的温度和降水对土壤湿度的年际异常非常敏感,土壤湿度的年际变化对中国春夏季气候及其年际变率均有显著影响。当不考虑土壤湿度年际异常时,模式模拟的春夏季平均温度、最高温度、最低温度在我国大范围内降低,春夏季降水在东部大部分地区明显减少,西部增加。而模式模拟的春夏季温度、降水年际变率在中国大部分地区减弱。但当考虑土壤湿度的年际变化,则能在一定程度上提高模式对气候年际变率的模拟能力。在进一步分析表明土壤湿度年际异常时,主要通过改变地表能量通量和环流场,对温度、降水产生影响。当不考虑土壤湿度年际异常时,地表净辐射通量减少,地表温度降低,感热通量减少。感热通量差值场的空间变化和温度差值场的空间变化一致,感热通量对温度有一定影响。而潜热通量差值场的空间变化和降水的差值场的空间变化一致,可见降水受地表潜热通量的影响。土壤湿度年际异常引起的环流场的变化也是导致气候变化的原因之一,地表能量和环流场年际变率的改变对春夏季气候年际变率存在一定影响。     

南太平洋海温异常及其气候影响的研究进展

随着海温观测资料的增多和资料同化技术的发展,南太平洋海温资料质量有了显著提高,这使得南太平洋逐渐成为科学家在研究海气相互作用及影响气候变化的因子时所关注的重点区域。文章系统地介绍了国内外对南太平洋海温（表层和次表层海温）异常变化特征的研究,涉及南太平洋海温异常年际和年代际变化的主要模态及特征,南太平洋海温异常与El Ni?o–Southern Oscillation、南极环状模的关系,以及南太平洋海温异常变化对大气环流和天气气候的影响（包括南太平洋对南美、东亚及中国地区天气气候的影响）等。在回顾已有研究成果的基础上,提出了一些需要深入研究解决的主要问题,以期引起大家对南太平洋海温异常变化研究的关注,促进对南太平洋海温异常及其气候影响的研究和深刻认识。     

北半球冬季极涡异常变化的时空特征

利用NCEP/NCAR再分析月平均高度场资料,计算了1948/1949-2009/2010年北半球冬季500～10 hPa的极涡环流指数,包括面积指数S、强度指数P和中心位置指数(λc,φc).分析了北半球冬季极涡在垂直高度上(共12层)的季、月气候态和异常态变化规律.结果表明:极涡面积和强度在不同高度上的大小变化不同,最大值出现的时间也存在差异,二者相关性不好,为两个相对独立的指数.极涡面积和强度的年代际变化趋势在上下层上也不一样,异常变化规律复杂;极涡中心位置上下层变化规律相同,主要在东半球80°N以北范围变化,在极点附近经度变化大,纬度变化小,纬度指数年代际变化明显,近10 a极涡明显偏南.从整体上看,极涡中心位置从500 hPa到10hPa形态上为逆时针、半径越向上越大的旋转变化.     

近49年来淮河流域降水异常及其环流特征

本文在对淮河流域降水气候特征分析的基础上，侧重研究了淮河流域夏季降水异常的周期性特征、年代际和年际变化特征，以及淮河流域多、少雨年的流场特征。研究发现，淮河流域夏季降水70年代中期以前偏多，70年代中期以后偏少；在周期性特征上有2．3年左右的主要周期和8年左右的次周期；淮河流域夏季降水异常与印度西南季风、东亚副热带季风以及冷空气异常有密切关系。     

西北太平洋台风频数异常年的气候背景分析

利用中国气象局整编的热带气旋资料、NCEP再分析资料和Scripps海温资料,分析了台风季西北太平洋台风频数发生年代际和年际异常时的气候背景特征,并且比较分析了造成台风频数发生年代际和年际异常的影响因子的异同。结果表明:台风频数的年代际变化主要和副热带高压和赤道西太平洋的温跃层海温有非常显著的关系,而年际变化则与副高、季风槽、越赤道气流以及赤道中东太平洋的混合层海温都有着密切的联系。     

关于ENSO本质的进一步研究

基于ENSO是热带太平洋海气相互作用产物的科学观点,一系列的分析研究表明:赤道太平洋次表层海温异常(SOTA)有明显的年际变化(循环),并且与ENSO发生密切相关;ENSO的真正源区在赤道西太平洋暖池,赤道西太平洋暖池正(负)SOTA沿赤道温跃层东传到东太平洋,导致El Nino(La Nina)的爆发;在暖池正(负)SOTA沿赤道温跃层东传的同时,将有负(正)SOTA沿10°N和10°S两个纬度带向西传播,从而构成SOTA的循环;热带太平洋SOTA年际循环的驱动者主要是由异常东亚季风所引起的赤道西太平洋纬向风的异常.进而,可以提出关于ENSO本质的一种新理论,即ENSO实质上主要是由异常东亚季风引起的赤道西太平洋异常纬向风所驱动的热带太平洋次表层海温距平的年际循环.       

陕西省2021年极端秋雨成因分析

利用NCEP/NCAR2.5°×2.5°的逐月再分析资料和NOAA提供的逐月海温资料等从海温异常、大尺度环流异常、水汽输送异常等角度分析了2021年秋季陕西降水异常偏多的原因,结果表明：（1）小波交叉谱分析显示Ni?o3.4区海温距平与陕西秋季降水存在2～4年的共振周期,前期冬季海温与次年秋季降水关系呈正相关的周期共振。（2）受双峰型La Ni?a事件影响,2021年9-11月副热带高压（下文简称“副高”）控制的范围明显偏大,副高脊线位置较气候态偏北1度,西伸脊点较气候态偏西23度,造成主雨带偏西偏北。（3）中低层西北太平洋到我国华北北部的异常反气旋,与孟加拉湾北侧异常的气旋中心,造成气流在我国西北地区东部异常辐合。（4）从水汽收支来看,陕西2021年秋季水汽净流入较气候态偏多66.7%,尤其是东边界的异常水汽输送,还增强了低层冷垫,利于暖湿气流在冷垫上爬升导致陕西降水较常年异常偏多。     

中国东部夏季分区降水对海温异常响应特征的研究

用刘征宇最新发展的广义平衡反馈方法结合经验正交分析和旋转经验正交分析法,研究中国东部6个分区夏季降水异常对各海盆海温异常(SSTA)模态的响应特征,探讨了东北区降水异常对SSTA的响应机制。结果表明:各分区降水异常对SSTA的响应特征有明显差异。东北区降水异常对热带太平洋SSTA的回应显著,当SSTA表现为类似El Niño模时,该区夏季降水增加;江淮区降水异常同时受到中纬度以及热带SSTA的强迫,对热带太平洋SSTA的类似La Niña Modoki模、北大西洋SSTA三极型模等回应显著;西南地区的降水异常主要与中纬度SSTA有密切关联。对流层高度场对热带太平洋SSTA类似El Niño模的直接回应在热带太平洋上空为显著正异常。通过东亚—太平洋型遥相关波列使东北地区上空高度场出现负异常,并在其西侧形成负异常中心,对流层低层为气旋性环流异常。这一环流回应与东北地区夏季降水偏多时的环流特征相近。     

青藏高原OLR的气候特征及其对北半球大气环流的影响

利用１９７４－１９９０年青藏高原地区地－气系统月平均射出长波辐射资料，采用ＥＯＦ方法分析了前３个特征向量场，得到了青藏高原地区地－气系统射出长波辐射的几种异常形式，阐述了它们的天气气候特征，并对不同气候区的持续 及其与北半球大气环流的关系作了研究。     

山东半岛夏季降水异常的环流型及影响因子分析

利用1961—2016年华东地区106个气象观测站的日降水数据和再分析资料,分析引起山东半岛夏季降水异常的大气环流型及其与前期下垫面因子（海温和土壤湿度）的关系,结果发现：1）当孟加拉湾出现西南风异常,日本列岛以南和贝加尔湖西南侧地区分别呈反气旋和气旋式环流异常时,加强了向山东半岛的水汽输送,配合区域大气上升运动异常最终导致山东半岛夏季降水偏多;反之,当孟加拉湾出现西北风异常,日本列岛以南和贝加尔湖西南地区分别呈气旋和反气旋式环流异常时山东半岛降水偏少。2）孟加拉湾和北太平洋中部关键区的对流层整层位势高度与下垫面海温自春季持续至夏季存在显著正相关,当两个地区的整层位势高度均呈正异常时,分别对应夏季孟加拉湾的强西风气流和日本列岛以南的反气旋环流异常。3）区域土壤湿度异常引起的感热和潜热通量异常,可能是引起贝加尔湖关键区位势高度和山东半岛局地对流异常的原因：贝加尔湖西南地区土壤湿度偏大时,其上空对流层位势高度为负异常;山东半岛地区土壤湿度偏大时,其上空对流层大气出现异常上升运动。4）利用关键区春季下垫面因子（海温和土壤湿度）建立山东半岛夏季降水的统计预测模型,留一交叉检验的距平同号率达到75%。这些结果可为山东半岛夏季降水预测提供重要参考。     

夏季北大西洋三极型海温异常与中国西南地区气温年际变化的联系

利用1951—2016年Hadley中心海温资料、NCEP/NCAR再分析资料和全国160站气温资料，研究了夏季北大西洋三极型海温异常与中国气温年际变化的联系及可能机制。结果表明，夏季北大西洋三极型海温异常与同期中国西南地区气温年际变化存在显著的负相关关系。夏季北大西洋“-+-”三极型海温异常激发的北半球中高纬欧亚遥相关波列，引起贝加尔湖地区位势高度升高，产生反气旋性环流异常，并引起东亚地区位势高度降低，产生气旋性环流异常。西南地区在对流层中下层位于贝加尔湖异常反气旋性环流的东部和东亚异常气旋性环流的西部，在两者的共同作用下，受异常偏北气流影响，有利于冷空气南下和堆积。与此同时，对流层高层的东亚副热带西风急流位置偏南，西南地区位于急流南侧的异常上升气流中。此种环流形势配置导致中国西南地区气温降低，反之亦然。     

On Multi-Timescale Variability of Temperature in China in Modulated Annual Cycle Reference Frame

The traditional anomaly (TA) reference frame and its corresponding anomaly for a given data span changes with the extension of data length. In this study, the modulated annual cycle (MAC), instead of the widely used climatological mean annual cycle, is used as an alternative reference frame for computing climate anomalies to study the multi-timescale variability of surface air temperature (SAT) in China based on homogenized daily data from 1952 to 2004. The Ensemble Empirical Mode Decomposition (EEMD) method is used to separate daily SAT into a high frequency component, a MAC component, an interannual component, and a decadal-to-trend component. The results show that the EEMD method can reflect historical events reasonably well, indicating its adaptive and temporally local characteristics. It is shown that MAC is a temporally local reference frame and will not be altered over a particular time span by an extension of data length, thereby making it easier for physical interpretation. In the MAC reference frame, the low frequency component is found more suitable for studying the interannual to longer timescale variability (ILV) than a 13-month window running mean, which does not exclude the annual cycle. It is also better than other traditional versions (annual or summer or winter mean) of ILV, which contains a portion of the annual cycle. The analysis reveals that the variability of the annual cycle could be as large as the magnitude of interannual variability. The possible physical causes of different timescale variability of SAT in China are further discussed.     

The Response of Anomalous Vertically Integrated Moisture Flux Patterns Related to Drought and Flood in Southern China to Sea Surface Temperature Anomaly

With the extreme drought (flood) event in southern China from July to August in 2022 (1999) as the research object, based on the comprehensive diagnosis and composite analysis on the anomalous drought and flood years from July to August in 1961-2022, it is found that there are significant differences in the characteristics of the vertically integrated moisture flux (VIMF) anomaly circulation pattern and the VIMF convergence (VIMFC) anomaly in southern China in drought and flood years, and the VIMFC, a physical quantity, can be regarded as an indicative physical factor for the "strong signal" of drought and flood in southern China. Specifically, in drought years, the VIMF anomaly in southern China is an anticyclonic circulation pattern and the divergence characteristics of the VIMFC are prominent, while those are opposite in flood years. Based on the SST anomaly in the typical draught year of 2022 in southern China and the SST deviation distribution characteristics of abnormal draught and flood years from 1961 to 2022, five SST high impact areas (i.e., the North Pacific Ocean, Northwest Pacific Ocean, Southwest Pacific Ocean, Indian Ocean, and East Pacific Ocean) are selected via the correlation analysis of VIMFC and the global SST in the preceding months (May and June) and in the study period (July and August) in 1961-2022, and their contributions to drought and flood in southern China are quantified. Our study reveals not only the persistent anomalous variation of SST in the Pacific and the Indian Ocean but also its impact on the pattern of moisture transport. Furthermore, it can be discovered from the positive and negative phase fitting of SST that the SST composite flow field in high impact areas can exhibit two types of anomalous moisture transport structures that are opposite to each other, namely an anticyclonic (cyclonic) circulation pattern anomaly in southern China and the coastal areas of east China. These two types of opposite anomalous moisture transport structures can not only drive the formation of drought (flood) in southern China but also exert its influence on the persistent development of the extreme weather.     

北半球月平均环流异常演变的相似韵律现象

本文用严格的统计方法和较长时间序列的观测资料对北半球月平均环流相似性的演变做了比较全面细致的分析。结果表明:两个不同年份的月平均距平场在某个起始月相似后相似性随之变差,但过了约半年左右变得又相似。这就是所谓的长期天气异常演变过程中半年左右的相似韵律现象。     

The modulated annual cycle: an alternative reference frame for climate anomalies

In climate science, an anomaly is the deviation of a quantity from its annual cycle. There are many ways to define annual cycle. Traditionally, this annual cycle is taken to be an exact repeat of itself year after year. This stationary annual cycle may not reflect well the intrinsic nonlinearity of the climate system, especially under external forcing. In this paper, we re-examine the reference frame for anomalies by re-examining the annual cycle. We propose an alternative reference frame for climate anomalies, the modulated annual cycle (MAC) that allows the annual cycle to change from year to year, for defining anomalies. In order for this alternative reference frame to be useful, we need to be able to define the instantaneous annual cycle: we therefore also introduce a new method to extract the MAC from climatic data. In the presence of a MAC, modulated in both amplitude and frequency, we can then define an alternative version of an anomaly, this time with respect to the instantaneous MAC rather than a permanent and unchanging AC. Based on this alternative definition of anomalies, we re-examine some familiar physical processes: in particular SST re-emergence and ENSO phase locking to the annual cycle. We find that the re-emergence mechanism may be alternatively interpreted as an explanation of the change of the annual cycle instead of an explanation of the interannual to interdecadal persistence of SST anomalies. We also find that the ENSO phase locking can largely be attributed to the residual annual cycle (the difference of the MAC and the corresponding traditional annual cycle) contained in the traditional anomaly, and, therefore, can be alternatively interpreted as a part of the annual cycle phase locked to the annual cycle itself. In addition to the examples of reinterpretation of physics of well known climate phenomena, we also present an example of the implications of using a MAC against which to define anomalies. We show that using MAC as a reference framework for anomaly can bypass the difficulty brought by concepts such as “decadal variability of summer (or winter) climate” for understanding the low-frequency variability of the climate system. The concept of an amplitude and frequency modulated annual cycle, a method to extract it, and its implications for the interpretation of physical processes, all may contribute potentially to a more consistent and fruitful way of examining past and future climate variability and change.     

Western Pacific Jet Stream Anomalies at 200 hPa in Winter Associated with Oceanic Surface Heating and Transient Eddy Activity

The relationships between the 200-hPa westerly jet stream anomalies over the East Asian coastal water- western Pacific(WPJS),and the oceanic surface heating and synoptic-scale transient eddy(STE)activity anomalies over the North Pacific in wintertime are examined by using ERA-40 and NCEP/NCAR reanalysis data.The analysis demonstrates that the surface heating and the STE anomalies have different patterns, corresponding to the three WPJS anomalous modes,respectively.In the first WPJS anomalous mode,the WPJS main part shows no robust anomaly.The anomalous westerly wind,occurring over the mid-latitude central-eastern Pacific past the date line is associated with the anomalous heating presenting both in the tropical central-eastern Pacific past the date line and the center of the North Pacific basin.Meanwhile,the STE anomaly appears around the region of the anomalous zonal wind.The fluctuation in jet strength shown in the second WPJS mode is strongly related to the heating anomaly in the Kuroshio Current region and the STE anomaly in the jet exit region.The third mode demonstrates a northward/southward shift of the WPJS,which has a statistical connection with a south-north dipolar pattern of the heating anomaly in the western North Pacific separated at 35°N.Meanwhile,the STE spatial displacement is in conjunction with jet shifts in the same direction.The heating anomaly has a close connection with the atmospheric circulation, and thus changes the mid-latitude baroclinicity,leading to the STE anomaly,which then reinforces the WPJS anomaly via internal atmospheric dynamics.