热带海温异常影响夏季环流的机制研究

利用正压涡度方程模式对赤道东太平洋和赤道西太平洋暖池区海温异常影响夏季大气环流的机制进行了研究,结果表明:太平洋海温异常会对大气环流产生明显的影响,我国上空环流受其直接影响较小,大气对赤道东太平洋海温升高的响应比对西太平洋暖池海温降低响应明显.西太平洋暖池海温降低和赤道东太平洋海温升高都使极涡明显减弱,对中低纬度大气高度场的影响相反.赤道东太平洋海温升高,中低纬度地区槽脊活动表现不明显,而西太平洋暖池海温降低,会使大气高度场产生明显的槽脊扰动.西太平洋暖池海温降低和赤道东太平洋海温升高,会使涡度场、经向风形成沿驻波波列传播的扰动场.西太平洋暖池海温降低和赤道东太平洋海温升高同时发生时,经向风场使北半球所有的地方都产生了扰动(两条波列路径仍然清楚),沿纬圈和经向都呈有规律的正负相间的分布,扰动表现为驻波特征.     

赤道东太平洋海温正异常对西太平洋副高影响的数值模拟研究

利用LASG九层大气环流谱模式及IAP两层大气环流模式，模拟研究了不同持续时间的赤道东太平洋海表温度正异常(海表温度异常的持续时间分别为1月份，1～2月份，1～4月份及1～8月份，其他月份为气候SST)对西太平洋副高的影响。结果表明，尽管海表温度异常的持续时间不同，但其引起的西太平洋副高的异常演变及其分布却十分相似；同时，季风区的异常降水(进而异常潜热释放)随时间的演变及其分布也存在一定的相似性(对应于不同持续时间的赤道东太平洋的海表温度正异常，5月份印度洋至西太平洋地区都表现出赤道辐合带北移偏晚的特征)；季风区降水的这种变化同西太平副高的异常是一致的，从而揭示出这两种现象有可能存在着某种联系。结果还表明，导致这种大气响应场对赤道东太平洋海表温度异常持续时间不敏感的一个重要原因是大气内部过程的影响:中纬大气的内部Rossby波源维持了热带地区激发的扰动在中高纬的存在，同时大气内部Rossby波源对赤道太平洋地区的海表温度异常持续时间表现出不敏感性，正是由于这种不敏感性才导致了响应场对赤道太平洋地区海表温度异常持续时间的不敏感性。模拟结果还表明，在夏季赤道东太平洋存在海表温度正异常的情况，尽管大气内部动力过程的作用十分重要，但夏季赤道东太平洋海表温度正异常对夏季西太平洋副高的影响却明显存在，因此，基于赤道太平洋地区海表温度异常的夏季西太平洋副高的可预报性受到赤道东太平洋海表温度正异常及大气内部动力过程的双重影响。模式的依赖性研究表明，模拟结果具有一定的普遍性。     

ENSO事件中次表层海温距平在10°N附近向西传播的机理

在最大温度距平的极值曲面上,对观测资料的分析表明,在这个曲面上的次表层海温距平,一般从西太平洋暖池附近沿赤道向东传播,然后在东太平洋95°W附近向两极传播,并在10°N附近(北半球比南半球清楚)向西传播,再在140°E暖池海域传向赤道,形成一个信号传播的回路。文章试图研究东太平洋次表层海温距平信号在10°N附近向西传播的可能机制。低空850 hPa风场的资料分析表明,当ENSO处在暖(冷)位相时,东太平洋沿岸附近将出现经向风,首先在经向风的吹引下,将产生沿岸的Kelvin波,进而在经向风的辐散(辐合)作用下,通过沿岸的上升(下沉)流在各个纬度激发出向西的Rossby波,但理论表明在与观测接近的周期性经向风作用下由Kelvin波产生的沿岸上升(下沉)流在10°N附近最大,因此在那个纬度附近Rossby波的振幅最大,更易将距平意义下的冷(暖)水传向西太平洋。     

长江中下游旱涝的环流型与赤道东太平洋海温遥相关波列特征

根据长江中下游地区夏季旱涝年前期冬、春季北太平洋海温分布特征进行分析研究 ,提出了影响区域性旱涝的海温“强信号”概念 ;探讨了北半球大气环流结构对赤道东太平洋海温异常响应问题 ,并研究了东太平洋海温与北半球夏、春季高度偏差场季尺度相关偏差场波列结构相关特征。研究结果表明 ,赤道东太平洋海温异常可能通过低纬walker环流引起赤道西太平洋区域性大气异常运动 ,从而产生遥响应环流型 ,形成类似PNA遥相关“大圆波列”。此类遥响应特征在西太平洋区域表现出与副热带高压、西风槽、阻塞高压等相关的系统的准定常经向波列。研究结果还表明此类经向波列结构描述了中高纬地区系统对低纬异常海温遥响应的动力学特征。应用 1997～ 1998年冬季实际海温资料 ,并在赤道中东太平洋地区引入实际海温异常的敏感性试验 ,较成功地模拟了 1998年夏季长江流域洪涝的降水分布特征。文中从统计、动力分析和数值模拟综合分析方法揭示出由前期东太平洋海温异常引起的大气环流变异 ,构成中国长江流域旱涝的物理图像及其动力学模型。     

El Nino事件发生和消亡中热带太平洋纬向风应力的动力作用 II.模式结果分析

为了分析ElNio事件发生和消亡中热带太平洋纬向风应力的动力作用，建立一个类似于Zebiak的简单热带海洋数值模式，在观测到的风应力异常的强迫下，模拟赤道太平洋地区1971年1月至1998年8月海表温度异常的变化。结果表明，模式对观测的Nio3区海表温度异常(SSTA)有很好的模拟能力。模拟和观测Nio3区SSTA之间的相关系数可达0.90。模式对ElNio事件期间赤道太平洋海表温度异常随时间变化也有较好的模拟能力。为了分析ElNio期间SSTA的空间分布及其随时间变化的动力学机制，还对19861989年ENSO循环期间赤道太平洋地区观测的SSTA的传播特征及其形成机制进行了分析。模式较好地模拟出了观测到的赤道太平洋地区SSTA的传播特征，即从1986年底至1987年4月，SSTA具有向东传播的特征，从1987年6月至1988年2月具有向西传播的特征。动力学分析的结果表明，赤道中西太平洋地区的纬向风应力异常对ElNio事件的发生和消亡具有重要作用。赤道中西太平洋地区的西风异常可强迫出东传的Kelvin波，这个东传的Kelvin波对正SSTA的东传起主要作用，当这个东传的Kelvin波到达东边界，由于东边界的反射作用，在东边界产生西传的Rossby波，这个西传的Rossby波对赤道中东太平洋地区正SSTA的西传起主要作用。东传Kelvin波和反射的Rossby波对ElNio期间赤道东太平洋正SSTA二次峰值的形成具有重要作用。     

一次El Niño背景下副高异常事件的基本特征

分析了 2019年一次El Ni?o事件发展的基本特征,并探讨了该次事件背景下副高偏强偏南的原因.研究发现:赤道中东太平洋纬向流反馈偏弱和西太平洋海域区域性的东风异常,都对该次事件表现出向中部型转变的趋势有一定程度的贡献.西太平洋海域上层大气的强烈下沉运动以及对流层低层存在的异常反气旋环流在一定程度上促进了副高的发展,在该次El Ni?o事件发展期间,导致西太平洋副高向南增强,位置偏南;Hadley环流下沉支的异常进一步加强了西太平洋副高的强度.2018年期间,从东太平洋海域西传的冷性Rossby波到达西太平洋海域且维持,产生异常Rossby波响应,同时2019年5月,MJO来到印度洋海域第8位相,西太平洋海域为反气旋性环流异常,二者共同影响,有利于热带西太平洋及我国南海地区出现异常的反气旋环流,进一步促进西太平洋副高加强西伸、强度偏强、位置偏南.     

赤道西太平洋海面增暖对早春北极平流层极涡的调控

平流层极涡异常对冬春季极端天气和极地臭氧亏损有重要指示意义。在1979～2020年ERA5再分析资料中,早春北极平流层极涡年际变率与热带太平洋海温第二模态（主要空间型为赤道西太平洋海温异常）有关。通过CAM5数值模拟,进一步揭示了赤道西太平洋海温异常影响平流层极涡的途径：冬春季赤道西太平洋增暖时,在暖海温区深对流降水加强,异常的潜热加热通过Matsuno-Gill响应在其西北侧激发了Rossby波（对流层上层的高压异常）。该Rossby波沿大圆路径在北太平洋调整了北半球最强的槽脊系统的强度和位置,从而使得经向风1波分量的振幅减小,经向风3波和温度3波分量的位相差增大。两者分别减弱了下平流层的1波和3波的波作用通量上传,更少的涡动热量通量向极输送促进了春季北极平流层极涡增强。     

热带太平洋西风异常对ENSO事件发生的作用

本文从观测资料对80年代两次ENSO事件产生过程中，热带太平洋西风异常及其对赤道中、东太平洋表层海温增暖的作用进行了分析和比较。分析结果表明:在这两次ENSO事件的产生过程中，赤道西太平洋上空均有较大的西风异常，并且它由赤道西太平洋向赤道中、东太平洋传播，随着西风异常从西向东传播，赤道中、东太平洋的表层相继增温。分析还表明，1982／1983年ENSO事件发生过程中，热带太平洋西风异常的强度要比1986／1987年热带太平洋西风异常强得多，这使得1982／1983 ENSO事件的强度比1986／1987_ENSO事件强得多。为了说明热带西太平洋西风异常对赤道中、东太平洋ENSO事件发生的作用，本文还利用IAP太平洋环流模式对西风异常在ENSO事件产生过程中的作用进行了数值模拟。模拟的结果说明了热带太平洋的西风异常对赤道太平洋暖水的向东传播和赤道中、东太平洋的增温起了很重要作用，这与观测事实分析一致。     

论热带纬圈半地转运动的建立

文中在赤道β平面上 ,在滤掉低频 Rossby波的情况下 ,研究了纬圈半地转运动的建立。指出 ,只有当运动的纬圈尺度很大时 ,非地转风分量才能随着重力惯性波的频散而消失 ,从而建立起纬圈半地转平衡。应用位势涡度不变式 ,给出了纬圈半地转适应后物理场的解。同时指出 ,Kelvin波 (对赤道对称情况 )和混合波的 Rossby波波段 (对赤道反对称情况 )将不参与适应运动 ,它们属于发展运动中的角色。     

厄尔尼诺和拉尼娜事件循环演变过程的资料分析研究

利用1955-2000年热带、副热带太平洋地区次表层温度距平资料,构造了温度距平极值深度分布曲面图,它很接近20°温度面的深度分布,因此有理由认为这一深度曲面很接近热带温跃层的深度面。在温度距平极值深度曲面上,分析了20世纪60年代后期以来所有El　Nino/La Nina事件正/负海温距平信号的分布和传播“轨迹”,发现如果以暖池次表层作为起点,则一般来说,暖水或冷水先是沿赤道极值深度面向东、向上传播或运动,到达赤道东太平洋海盆边界附近后,在那里停留几个月,然后转北运动,在北纬10度左右再折向西运动到西太平洋转向南返回到暖池,即在赤道北侧形成闭合回路。温度距平运动一圈需时2-4年。如果暖（冷）水的温度距平都很强,就会在2-4年的时间上出现两次相邻的El　Nino（La Nina）事件,但可能是由于大气或海洋环境条件不合适,温度距平的强度在运动过程中有时会减弱,就不能形成El　Nino（La Nina）事件,但暖（冷）水运动的“轨迹”仍可辨认。由于暖、冷水绕环路的运动交替出现,El Nino（La　Nina）爆发前,在赤道西太平洋出现正（负）距平信号的同时,在东太平洋北纬10度左右会有负（正）距平信号出现,并且当正（负）距平信号向东传播时,负（正）距平信号向西传播,在赤道上表现为2-4年间隔的El Nino（La Nina）交     

Rossby wave propagation into the tropics in two GFDL general circulation models

During the northern winter the eastern Pacific is characterized by upper level westerly flow extending from the equator into the midlatitudes of both hemispheres. Theoretical and simple modeling studies suggest that such a region should favor the penetration of Rossby waves into the tropics from higher latitudes. Observational results by Kiladis and Weickmann using 200 mb data indicate that Rossby waves do indeed propagate freely into the tropical eastern Pacific during the northern winter from the Asian jet exit region. They also confirmed that cross-equatorial dispersion of energy from the Northern into the Southern Hemisphere occurs frequently. The present study examines these interactions in climatological runs of two GFDL GCMs. The northern wintertime mean states of these models are characterized by a rather realistically simulated upper level westerly regime in the tropical Pacific. Despite the relative weakness of the Asian jet and wave activity with respect to observations, propagation of Rossby waves into the tropics is present in both models, and these waves are strongly positively tilted as seen in the observations. A momentum budget of the zonal wind and E vector diagnostics over the tropical Pacific indicate that these transients are an important component of the momentum balance of the equatorial westerlies in both the observations and in the models.This paper was presented at the Second International Conference on Modelling of Global Climate Variability, held in Hamburg 7–11 September 1992 under the auspices of the Max Planck Institute for Meteorology. Guest Editor for these papers is L. Dümenil     

Meridional Wind Stress Anomalies over the Tropical Pacific and the Onset of El Ni?o Part Ⅱ: Dynamical Analysis

The data analyses in the first part of this study have shown that the sea surface temperature anomalies (SSTA) in the eastern equatorial Pacific are significantly correlated with the preceding anomalous convergence of the meridional wind stress near the equator. In order to understand the dynamical role of the convergent meridional wind stress anomalies in the El Nino occurring, an ideal wind stress which converges about the equator is set up based on the observations revealed in the first part. A simple dynamical model of tropical ocean is used to study the response of the tropical ocean to the convergent meridional wind stress. The results show that the convergent wind stress in the eastern equatorial Pacific is favorable for the occurrence of El Nino. When the convergent wind stress exerts on the tropical ocean, the westward propagating Rossby wave is excited, which, on the one hand, makes the mixed layer near the equator become thicker. On the other hand, the westward oceanic currents associated with the Rossby wave appear in the vicinity of the equator. The oceanic currents can drive the upper layer sea water to transfer to the west, which is favorable for the sea water to pile up in the western equatorial Pacific and to accumulate energy for the upcoming warm event.     

On the Mechanism of the Locking of the El Nino Event Onset Phase to Boreal Spring

The mechanism of the locking of the E1 Nino event onset phase to boreal spring （from April to June） in an intermediate coupled ocean-atmosphere model is investigated. The results show that the seasonal variation of the zonal wind anomaly over the equatorial Pacific associated with the seasonal variation of the ITCZ is the mechanism of the locking in the model. From January to March of the E1 Nino year, the western wind anomaly over the western equatorial Pacific can excite the downwelling Kelvin wave that propagates eastward to the eastern and middle Pacific by April to June. From April to December of the year before the E1 Nifio year, the eastern wind anomaly over the equatorial Pacific forces the downwelling Rossby waves that modulate the ENSO cycle. The modulation and the reflection at the western boundary modulate the time of the transition from the cool to the warm phase to September of the year before the E1 Nifio year and cause the strongest downwelling Kelvin wave from the reflected Rossby waves at the western boundary to arrive in the middle and eastern equatorial Pacific by April to June of the E1 Nino year. The superposition of these two kinds of downwelling Kelvin waves causes the El Nino event to tend to occur from April to June.     

热带太平洋经向风应力异常与El Nio的发生——(Ⅱ)动力学分析(英文)

第一部分（Ｚｈａｎｇ ｅｔ ａｌ，２００１）的资料分析表明，Ｅｌ Ｎｉｏ事件发生之前在赤道中东太平洋存在着显著的异常经向风应力辐合、为了分析这种超前的辐合经向风应力距平在其后的ＥｌＮｉｏ事件发生中的动力作用，本文利用简单热带海洋动力学模式，从动力学上研究了热带海洋对关于赤道辐合的理想经向风应力强迫的响应，指出赤道东太平洋出现在Ｅｌ Ｎｉｏ事件之前的辐合经向风应力异常有利于Ｅｌ　Ｎｉｏ事件的发生。辐合的经向风应力强迫作用于热带海洋，会激发出西传的Ｒｏｓｓｂｙ波，使得赤道附近的海洋混合层变厚。由于耗散的影响，最大的增厚区位于强迫区域。当这个强迫作用于赤道东太平洋时，这将有利于以 Ｎｌ　Ｎｉｏ事件发生；另一方面，Ｒｏｓｓｂｙ波响应在赤道及其附近使得表层海水向西流动，中东太平洋表层水的不断向西输送有利于表层水在西太平洋堆积，为后来暖事件的发生累积能量。     

On the Mechanism of the Locking of the El Nio Event Onset Phase to Boreal Spring

1. Introduction The observed facts show that the ENSO cycle has obvious phase-locking and oscillates irregularly (An and Wang, 2001; Kaplan et al., 1998). Based on Zibiak and Cane's (1987) model (hereafter, the Z-C model) and simple, coupled ocean-atmosph…     

Annual ENSO simulated in a coupled ocean–atmosphere model

Using an output from 200-year integration of the Scale Interaction Experiment of EU project-F1 model (SINTEX-F1), the annual ENSO reproduced in the coupled general circulation model is investigated, suggesting the importance of reproducing an annual cycle in realistically simulating ENSO events. Although many features of the annual ENSO are reproduced, the northward expansion of sea surface temperature anomaly (SSTA) in the eastern tropical Pacific stays south of the equator. It is suggested that this model bias is due to the excitation of the too strong Rossby waves in the southeastern tropical Pacific, which reflect at the western boundary and intrude into the eastern equatorial Pacific. The zonal wind stress anomaly along the equator also plays an important role in generating the equatorial Kelvin waves. The amplitude of SSTA for the annual ENSO mode is reproduced, but its variance is only 20% of the observation; this is again due to the lack of northward migration of seasonal SSTA in the equatorial region and weaker coastal Kelvin waves along South America. Remedies for the model bias are discussed.     

Resonance of baroclinic waves in the tropical oceans: The Indian Ocean and the far western Pacific

The Indian Ocean has a particularity, its width is close to half the wavelength of a Rossby wave of biannual frequency, this coincidence having been capitalized on by several authors to give the observations a physical basis. The purpose of this article is to show that this is not the case since the resonance of tropical baroclinic waves occurs in all three oceans. This is because the westward-propagating Rossby wave is retroflexed at the western boundary to form off-equatorial Rossby waves dragged by countercurrents before receding and turning back as a Kelvin wave. Thus a quasi-stationary baroclinic wave is formed, whose mean period is tuned to the forcing period. Two independent basin modes resonantly forced are highlighted – 1) a nearly symmetric zonal 1/2-yr period Quasi-Stationary Wave (QSW) that is resonantly forced by the biannual monsoon. It is formed from first baroclinic mode equatorial-trapped Rossby and Kelvin waves and off-equatorial Rossby waves at the western antinode. This QSW controls the Equatorial Counter Current at the node. The Indian Ocean Dipole (IOD) results from a subharmonic mode locking resulting from the coupling of this QSW and the 2nd, 3rd and 4th baroclinic modes - 2) a 1-yr period QSW formed from an off-equatorial baroclinic Rossby wave, which is induced from the southernmost current of the Indonesian Throughflow through the Timor passage, propagating in the southern and northern hemispheres: the drivers are south-easterlies in the southern hemisphere and monsoon wind in the northern hemisphere.