夏季欧亚中高纬环流持续异常事件的Rossby波传播特征

利用西风波导结构以及波作用通量, 探讨了夏季欧亚一类中高纬持续异常环流所对应的Rossby波的能量频散特征。中高纬度对流层上层存在结构较为复杂的弱波导, Rossby波能量频散过程基本上与该弱波导结构一致。Rossby波传播特征在不同时期以及两种环流型 （E型和C型) 之间存在显著差异: (1) 在梅雨前期, 与E型环流对应, Rossby波从南欧气旋式异常环流中心传播到乌拉尔山正高度异常中心, 并且波作用通量在乌拉尔山西侧辐合, 形成该地区正高度异常环流。乌拉尔山持续异常中心东侧重新激发出Rossby波, 并传播至贝加尔湖和鄂霍次克海地区, 维持对应的异常环流。与C型异常环流对应, Rossby波活动非常活跃。该型三个活动中心呈现高纬－中纬－高纬的分布特征, 这与波导结构密切相关。 (2) 在梅雨期, Rossby波的传播对两类持续异常环流的作用更加明显, 其传播路径基本上在处于极区和偏向中纬度一侧的两个“波障碍区”之间的带状西风波导区中。Rossby波从乌拉尔山活动中心向东传播, 最终形成贝加尔湖和鄂霍次克海地区的持续异常环流。在C型维持过程中则还存在另一种强迫因子。在C型中, Rossby波从乌拉尔山活动中心向中纬度传播, 并在亚洲急流中向东传播至东亚地区。 (3) 在后汛期, 在欧亚大陆上纬向“波障碍区”的增加使得Rossby波活动减弱。E型异常环流型的鄂霍次克海活动中心向东扩展到北太平洋, 但来自上游的Rossby波传播只作用于该活动中心的西北侧部分。C型中Rossby波的传播在乌拉尔山活动中心地区变弱。在夏季各个时期, E和C型持续异常环流对应着不同位相的EAP (或PJ) 型, 但并没有Rossby波从中纬度向北传播至鄂霍次克海地区的现象。     

Variations in Wave Energy and Amplitudes along the Energy Dispersion Paths of Nonstationary Barotropic Rossby Waves

The variations in the wave energy and the amplitude along the energy dispersion paths of the barotropic Rossby waves in zonally symmetric basic flow are studied by solving the wave energy equation,which expresses that the wave energy variability is determined by the divergence of the group velocity and the energy budget from the basic flow.The results suggest that both the wave energy and the amplitude of a leading wave increase significantly in the propagating region that is located south of the jet axis and enclosed by a southern critical line and a northern turning latitude.The leading wave gains the barotropic energy from the basic flow by eddy activities.The amplitude continuously climbs up a peak at the turning latitude due to increasing wave energy and enlarging horizontal scale(shrinking total wavenumber).Both the wave energy and the amplitude eventually decrease when the trailing wave continuously approaches southward to the critical line.The trailing wave decays and its energy is continuously absorbed by the basic flow.Furthermore,both the wave energy and the amplitude oscillate with a limited range in the propagating region that is located near the jet axis and enclosed by two turning latitudes.Both the leading and trailing waves neither develop nor decay significantly.The jet works as a waveguide to allow the waves to propagate a long distance.     

大气动力学中三种Rossby波作用通量的特征差异和适用性比较

大气动力学诊断Rossby波的传播时,通常用波作用通量来表示。常用的三种波作用通量分别为Plumb波作用通量,T-N波作用通量和局地E-P通量。本文详细讨论了这三种方法的特征差异,并结合2016年1月的一次寒潮事件,比较了三种方法在该事件中的适用性。结果表明:1)Plumb波作用通量的纬向分量较大而经向分量较小,适用于振幅较小的纬向均匀的西风带Rossby长波的诊断。2)T-N波作用通量是对Plumb波作用通量的改进,经向分量得以增强,能更好地描述纬向非均匀气流中的较大振幅的西风带Rossby长波扰动。T-N波作用通量计算时,背景场取多年平均的当月气候场较合适,能更好地反映当前季节内的Rossby波传播异常。3)局地E-P通量可以诊断一段时间内天气尺度瞬变波对背景场(定常波)总的调控作用,但无法直接反映Rossby长波的逐时演变(T-N波或Plumb波作用通量则可以)。     

正压大气中的代数Rossby孤立波

本文研究了基本气流具有线性弱切变的非线性Rossby波,得到了一个非线性发展方程为Kubota方程,在一定的条件下,可变为Benjamin-Ono方程,并指出当代数Rossby孤立波的振幅越大时,代数Rossby孤立波的传播速度越小,基流切变越强,代数Rossby孤立波越慢,同时我们还指出在代数Rossby孤立波的振幅满足一定的条件下,代数Rossby孤立波才随纬度的增高(β减小)而减慢。并且代数Rossby孤立波的结构与大气中的偶极子阻塞是一致的。     

大地形对Rossby波波射线的影响

本文利用Ｒｕｎｇｅ－Ｋｕｔｔａ方法计算了大地形对定常、非定常低频Ｒｏｓｓｂｙ波波射线的影响，计算结果显示，地形对Ｒｏｓｓｂｙ波波射线有重要影响。对位于地形上游的波源，定常波波射线在传播过程中，遇到地形时，会绕过地形偏向高纬度传播并加密波射线，地形起阻挡屏障作用；波源位于地形中心时，东西走向的地形使波射线发生分支现象，南北走向地形没有这种现象产生。文中还计算了地形存在下，周期为５０ｄ的低频Ｒｏｓｓｂｙ波波射线。结果显示，地形对低频波波射线的影响似乎更复杂。     

Stationary Rossby wave propagation in a shear flow along a reflective boundary

Summary This study investigates the impact of lateral boundary conditions on the propagation and dispersion of locally excited Rossby waves in a zonally periodic, barotropic, quasigeostrophic channel model on the β-plane. We use basic flows with either a linear meridional shear or a jet-like profile. On the southern boundary of the channel we impose either a rigid wall or a radiation condition, whereas the northern sidewall is permeable for Rossby waves. We compare the numerical solutions found for a reflecting southern boundary in a weakly dissipative flow to the solutions obtained from a WKB-analysis for the corresponding unforced nondissipative situation. Furthermore, we compare the generalized Eliassen-Palm flux vectors to the ray paths of Rossby wave packets, obtained from WKB ray tracing. In particular, we focus our investigation on the two-dimensional structure of trapped modal waves and wavetrains in a simple linear numerical model. Summarizing our results, we find that along the reflective wall, trapped modal wave structures as well as reflected wavetrains occur with characteristics (e.g., wavenumbers, turning latitudes) similar to the ones computed using asymptotic methods. In a linear sheared flow wave packets are trapped for all zonal wave numbers in contrast to a jet-like mean flow which has a selective effect on the waves; i.e., a turning latitudes phenomenon between the coast and the flow maximum occurs for short waves, while long waves can propagate freely across the zonal mean flow. This comes out clearly when studying the stream lines of the Eliassen-Palm flux vectors of the numerical model simulations. Furthermore, due to the reflected wave activity, the dispersion of Rossby waves is influenced by the southern boundary condition not only in the vicinity of the border but also in regions away from the boundary. These results appear to be important on the one hand for the existence of trapped Rossby waves in large-scale oceanic shear flows along a zonally oriented coast. And, on the other hand for large-scale boundary waves in conceptional atmospheric channel models which can lead to unwanted resonance effects. Received July 18, 2000/Revised June 9, 2001     

全球扰动的结构、演变及其球面Rossby波包表示

利用按谱函数展开的方法,计算和分析了正压球面Rossby波的连续谱和离散谱的波包结构、演变和传播特征,发现无论是结构、演变还是传播,连续谱波包和离散谱波包都很不相同.连续谱波包的传播速度不仅大小而且方向都随纬度变化;离散谱波包的传播速度只有大小随纬度变化,其方向在任何纬度上都是向西的.连续谱的波包和离散谱的波包在初始时刻虽然都表现为子午圈上不规则的波动,但随着时间的增加,二者的变化规律不同,连续谱的波包具有局部特征,主要表现在两个半球的中高纬地区,且随时间振幅迅速衰减;而离散谱的波包具有全球性质.将二者与整个扰动波包进行比较,发现:在中高纬度地区,连续谱波包的结构与扰动波包的结构相似,而在赤道地区,离散谱的波包与扰动波包相似.     

旋转正压大气中的Rossby波射线

本文将缓变介质中波动的传播理论应用于Rossby波。在基流和不同走向地形假设下，计算了Rossby波射线路径及沿射线波数的变化。结果表明大尺度地形对Rossby波射线有显著影响。     

Atmospheric circulation associated with extreme generalized frosts persistence in central-southern South America

Generalized frosts (GF) in central-southern South America have a strong impact due to their spatial extension, and they are especially important when they become persistent. This paper aims at identifying the atmospheric circulation features that determine the extreme GF persistence, i.e. very persistent and without persistence, and the differences between them, during the 1961–1990 winters. Since the GF without persistence group outnumbers the other one, two subgroups are composed with events selected from winters with maximum and minimum frequency of GF occurrence, respectively. Additionally, the individual event of July 1988 within the very persistent GF group is analyzed due to its exceptional persistence. GF persistence is mainly conditioned by two large-scale dynamic factors. One is the Rossby wave train propagation across the Pacific Ocean, and the other one is the location with respect to the continent and the magnitude of the confluence in the jet entrance region in subtropical latitudes. A predominantly meridional Rossby wave train propagation with a confluence region to the west of the continent prior to the event favors GF with intermediate (null) persistence depending on the greater (lesser) jet acceleration. This is conditioned by the magnitude of the confluence, which, in turn, depends on the disposition of the wave train propagation pattern. Instead, an essentially zonal propagation with a confluence region to the east of the continent favors the GF persistence for several days, yet if there is no confluence the event does not persist. The greatest persistence of an event combines the confluence/diffluence of the jet entrance/exit region, which depends on the disposition with respect to the continent of the zonally propagating Rossby wave trains.     

South Indian Ocean Rossby Waves

ABSTRACT

South Indian Ocean Rossby waves (SIO-RW) are identified in the Global Ocean Data Assimilation System (GODAS) 1.5–7?yr filtered sea surface height (SSH) time series. There is a persistent three-year oscillation in the 5°–15°S latitude band from 55° to 85°E. Field correlations show little coupling at 90°E, but as the SIO-RW undulates westward at approximately 0.19?m?s^?1 across the mid-basin, a northwest–southeast axis of warm sea surface temperatures (SSTs) and deep convection forms. Many teleconnections in earlier work are confirmed: interannual pulses of zonal wind in the eastern basin trigger the SIO-RW via anticyclonic wind stress curl. New insights derive from an understanding of links with the upper troposphere. As the SIO-RWs move westward with the onset of an El Niño in the Pacific, increased convection over the north Indian Ocean corresponds to reduced evaporation and SST warming. Mid-tropospheric heating T′?>?2°C over the northwest Indian Ocean accelerates the southern sub-tropical jet to greater than 10?m?s^?1 over the southeast Indian Ocean, reinforcing the anticyclonic vorticity. The downstream acceleration of the jet generates upper-level divergence and moist convection over the western basin, anchoring an atmospheric Rossby wave in a northwest–southeast alignment underpinned by differential propagation of the SIO-RW. As the ocean Rossby wave reaches Africa, the coupling fades and transitions. What distinguishes Indian Ocean from Pacific Ocean Rossby waves are their southern latitude and higher frequency. The tropical mid-tropospheric heating that accelerates the southern sub-tropical jet shifts westward in tandem with the SIO-RW.     

急流与定常强迫Rossby波包和大气中的遥相关

本文利用波包概念和WKB方法,给出在一定地形和基流背景条件下Roosby波包的整体特性,并得到波包的发展方程和条件。应用波包发展条件于西南和东南急流的背景流场,提出波包断裂和波传播波道分叉的概念,即:根拐Rossby波包在急流区所处的位置和定常波包所须满足的条件,其槽(脊)线要变形,产生弯曲、断裂直至分离,波传播波道从而也发生分叉,产生两个波包和两支波道。对于西南风急流,一个波包向高纬传播,并可上升到平流层;另一个向低纬传播,但不如前者传得远,升得高。应用西南风急流中Rossby波包演变和波道分叉的这种特性,可以解释Wallace等提出的PNA型和EU型两种遥相关,从而为这两种类型的遥相关提供了一种物理机制。     

Three-dimensional dynamic features of two arctic oscillation types

We investigated the differences between stratospheric (S-type) and tropospheric (T-type) Arctic Oscillation (AO) events on the intraseasonal time scale, in terms of their influences on surface air temperature (SAT) over the Northern Hemisphere and the dynamic features associated with their spatial structures. S-type AO events showed a stratosphere-troposphere coupled structure, while T-type events exhibited a stratosphere-troposphere uncoupled structure. The annular SAT anomalies over the Northern Hemisphere were found to be associated with S-type AO events, whereas such an annular feature was substantially destructed in T-type AO events. The different horizontal structures in the troposphere of the two types could mainly be attributed to transient eddy feedback forcing. As for the vertically uncoupled structure of Ttype events, the underlying dynamical features that differentiate them from S-type events lie in the vertical propagation of zonally confined Rossby waves. In T-type events, the zonally confined Rossby wave packets can emanate from the significant height anomalies over Northeast Asia, where one vertical waveguide exists, and then propagate upward into the stratosphere. In contrast, such a vertical propagation was not evident for S-type events. The stratospheric anomalies associated with the upward injection of the zonally confined Rossby waves from the troposphere in T-type events can further induce the anomalous vertical propagation of planetary waves (PWs) through the interference between the climatological-mean PWs and anomalous PWs, leading to the final stratosphere-troposphere uncoupled structure of T-type events.     

Vortex Rossby Waves in Asymmetric Basic Flow of Typhoons

Wave ray theory is employed to study features of propagation pathways(rays) of vortex Rossby waves in typhoons with asymmetric basic flow, where the tangential asymmetric basic flow is constructed by superimposing the wavenumber-1 perturbation flow on the symmetric basic flow, and the radial basic flow is derived from the non-divergence equation. Results show that, in a certain distance, the influences of the asymmetry in the basic flow on group velocities and slopes of rays of vortex Rossby waves are mainly concentrated near the radius of maximum wind(RMW), whereas it decreases outside the RMW. The distributions of radial and tangential group velocities of the vortex Rossby waves in the asymmetric basic flow are closely related to the azimuth location of the maximum speed of the asymmetric basic flow, and the importance of radial and tangential basic flow on the group velocities would change with radius. In addition, the stronger asymmetry in the basic flow always corresponds to faster outward energy propagation of vortex Rossby waves. In short, the group velocities, and thereby the wave energy propagation and vortex Rossby wave ray slope in typhoons, would be changed by the asymmetry of the basic flow.     

Teleconnection patterns and Rossby wave propagation associated to generalized frosts over southern South America

Based on previous observational studies of the mean atmospheric circulation leading to generalized frosts (GF) in central Southern South America, it is possible to establish a hypothesis that specific large scale patterns are associated to the frequency of occurrence of these events through the propagation of Rossby waves remotely excited. This hypothesis is tested here through a teleconnection analysis for austral winters which present an extreme frequency of occurrence of GF in southeastern South America, particularly over the Wet Pampa area in Argentina. Rossby wave propagation regions are identified for two basic states given by the composition of winters with maximum and minimum frequency of GF occurrence, during the 1961–1990 period. The stationary wavenumber K _s indicates the regions where the Rossby wave propagation is permitted and those where it will be inhibited (K _s = 0), highlighting the importance of the jets as waveguides. Nevertheless, differences exist between both basic states analyzed. These differences indicate that the locations for wave generation and its later evolution are conditioned by the basic state. Results are validated through a baroclinic model, which simulates the Rossby wave patterns responsible for the teleconnection. Numerical experiments confirm that the principal wave activity takes place inside the subtropical and polar jets. In particular, for the basic state with maximum frequency of GF occurrence, the wave trains propagating inside the subtropical and polar waveguides merge just before entering the continent, as shown by the observations prior to the occurrence of GF events. This configuration favors the development of an intense south wind anomaly with large meridional extension which results in the intensification of anticyclonic circulation in southern South America. A conceptual model is presented to summarise all these results.     

地形强迫对大气长波调整的可能影响

地形作为大气的外部强迫,其动力和热力作用对波动结构演变及极端天气出现都有不能忽视的作用。本文通过数值求解考虑地形强迫的β平面正压准地转位势涡度方程,探讨了地形强迫作用对大气长波调整的可能影响,结果表明:同非线性作用和纬向非均匀基流作用一样,无基流情形下具有纬向差异的地形分布影响了大气长波结构的演变,也能强迫出大气长波调整现象。大气长波调整依赖于地形的高度和地形分布,地形越高,长波越容易出现波数的调整;地形波数越大,即地形结构复杂,越不易出现波数变化。大气长波调整还与纬度有关,纬度越高,β越小,地形强迫作用越突出,长波调整容易出现;反之,低纬度以β效应为主的线性波动不易出现波数调整。大气长波调整对波动初始波动的振幅不敏感,但依赖于波动的初始结构。此外,有基流作用时,地形强迫还是诱发定常波的重要因素,且定常波流场结构依赖于地形高度分布,与波动初始结构无关。     

北大西洋涛动对新疆夏季降水异常的影响

利用1961~2003年NCEP/NCAR再分析和新疆75个气象站月降水资料,分析新疆夏季降水与沿西亚副热带西风急流Rossby波和北大西洋涛动（NAO）的关系,研究表明,夏季斯堪的纳维亚半岛-中欧—西亚和中亚的准静止波传播是联系NAO与沿西亚副热带西风急流波活动和新疆夏季降水变化的纽带。通过波作用量的动力学诊断分析,讨论了夏季NAO正、负位相异常年准静止波传播特征和差异,夏季NAO强弱活动影响斯堪的纳维亚半岛EP通量散度强度和位置异常,该区EP通量散度强度和位置异常导致强辐散中心在中高纬向东传播的准静止波和沿副热带西风急流准静止波活动变化,从而影响新疆夏季降水。     

旋转正压大气中的Rossby孤立波和偶极子阻塞

大气中的阻塞动力学一直是大气动力学中所要解决的重要问题之一,随着数学的发展,阻塞动力学的研究也取得了较大的进展。大气中的阻塞可以分为两类:一类是单个非偶极子阻塞(只存在高压或低压),另一类是偶极子阻塞(高压的南侧存在闭合的低压)。关于偶极子阻塞的动力学研究是在80年代以后才进行的。为了解释大气中所出现的偶极子阻塞,Mcwilliams(1980)提出了Equivalent     

南海夏季风爆发的动力过程研究

利用1958—1997年的NCEP/NCAR再分析资料,以南海季风爆发日为临界日期,计算了40年合成的季风爆发前月平均带状基流;在该基流上,计算了球面正压涡度方程中Rossby波的稳定性;并用谱函数展开法定义和计算了发展型波包的演变。结果显示：南海夏季风爆发前气候平均场上有球面Rossby波的正压不稳定,该不稳定主要由南半球的西风急流所激发,且不稳定扰动的最大振幅均出现在南半球西风急流以南。球面Rossby波发展型波包的最大振幅随时间会由两个半球的中高纬度向低纬扩展,虽然不能越过赤道,却激发了热带地区的积云对流,积云对流的爆发并向季风区传播,加速了大气环流的调整,其结果造成了南海夏季风的爆发。可见,南海夏季风的爆发虽是局地现象,但其爆发原因却是全球性的。     

青藏高原热力作用下的非绝热Rossby波

从含非绝热项的准地转运动方程组出发，分析了青藏高原大尺度热力作用下非绝热Rossby波的一些性质，从理论上证明当背景西风气流为正压时，冬季高原冷却作用有利于Rossby波的经向传播，夏季高原大尺度热力作用不利于波动的经向传播。非绝热Rossby波的频率方程说明冬季高原的热力作用是中纬季节内振荡的重要激发机制。同时，在背景西风气流为纯斜压条件下，求解了高原热力作用下非绝热Rossby波的频率，并由频率方程说明冬季高原热力作用有利于波动向不稳定方向发展，而夏季高原的大尺度热力作用对波动稳定性的影响存在临界值。