正压准地转模式中大地形作用下的低频波

利用包含大地形和常速纬向基本气流的正压准地转位涡度方程,研究了大地形对低频波激发的作用,结果表明,起作用的地形因子主要是地形的最大高度和地形坡度。地形最大高度的作用主要是使Rossby波趋向低频,而地形坡度的作用主要是对Rossby波的稳定性起决定作用,同时适当的地形坡度也可导致低频波的形成。而常速纬向基流在总体上的作用是使波动变得趋向低频,且西风基流更有利于低频（30～60天）波的形成。从纬向波数上看,纬向3波以上的波动更容易出现低频（30～60天）。     

INFLUENCES OF TOPOGRAPHY ON BAROCLINIC SOLITARY ROSSBY WAVES IN A MULTILEVEL MODEL

The KdV equation with topography included in an N-level model is derived. It is shown that if the topography ex-ists. the KdV equation may describe the solitary Rossby waves in the case of basic current without vertical shear, and itis no necessary to introduce the MKdV equation. The results of calculations show that the change of horizontal shearpattern of basic flow may cause an important change of the streamline pattern of the solitary waves with the oddmeridional wavenumber m, and has no effect for the even meridional wavenumber m. The vertical shear increases thesteepness of the barotropic solitary modes, and it has a complicated effect on the baroclinic modes. The influences oftopographic slope on the solitary waves are very great. The southern and northern slopes of topography may cause dif-ferent solitary wave patterns, with the effect of northern slope greater. The effect of Froude number on the solitarywaves is generally to steepen the solitary waves, however, the effect also depends on the meridional wavenumber m andthe modes of solitary wave.     

近共振地形强迫Rossby孤立波

利用扰动展开和时空伸长变换导得了包括地形强迫的非齐次ＫｄＶ方程，讨论了近共振地形强迫Ｒｏｓｓｂｙｙ孤立波的产生，及其与自由孤立波的相互作用，得到了一些有意义的结果，显示出地形对扰动具有明显的增幅作用，在某种程度上可以解释局地地形在阻塞高压形成中的作用。     

Some evidence of organized flow over natural waves

Measurements of the flow characteristics at 2 m over unobstructed wave surfaces on Lake Michigan were made using an anemometer-bivane as a velocity sensor. During one 40-min period of measurement, significant energy concentration was observed at the frequency of dominant surface waves in the vertical and cross wind spectra. Cross spectra between the surface elevation and vertical motions in the flow indicate that the surface lags the vertical motions by about 55 ° at the frequency of dominant waves.     

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.     

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。     

地形对长波和超长波不稳定发展的影响

图3.2.1—3.2.5表示了地形对长波和超长波移动和发展影响的一般规律。如以地形脊对东移西风冷槽的影响为例,当地形相当涡度和扰动涡度的振辐比a_m/a_(20)较小时,在它越过地形脊时,首先流场槽减弱而温度槽加强,减弱的流场槽以较快的速度移动,而温度槽则相对减慢,越过地形脊后,流场槽又重新增强。 我们根据地形的影响,初步讨论了一锢囚气旋在向风坡填塞,在背风坡又重新产生的物理过程。超长波的斜压不稳定的不能发展,是由于温度场东进和流场西退造成的。根据地形脊对超长波脊移动的影响,可以推测,在两个地形超长波脊之间的地区,最有利于超长波脊的不稳定发展。阻塞脊出现频数的地理分布的观测结果和理论推测有很好的一致性。     

青藏高原东北侧干旱的数值试验

用谱方法（Ｔ４２）求解半球球面无辐散正压涡度方程,采用实际的干旱环流资料,分别在有地形和无地形的情况下,求出其对应的干旱环流型的强迫场,模拟了在强迫场的作用下干旱环流的形成、维持情况及在强迫场消失后干旱环流型的崩溃情况。结果表明：（１）强迫场在干旱环流型的形成、维持及崩溃过程中起重要作用;（２）青藏高原的存在使其东北侧干旱形成和崩溃均加快。     

INTERACTION OF TOPOGRAPHY WITH SOLITARY ROSSBY WAVES IN A NEAR-RESONANT FLOW

An inhomogeneous KdV equation including topographic forcing is derived by usingperturbation expansions and stretching transforms of time and space.The generation of forcedsolitary Rossby waves by topography in a near-resonant flow and their interactions with freesolitary waves are discussed,and some interesting results are obtained.The numerical resultsshow that the topography has obvious effect on enhancing the amplitude of disturbances,and itmay explain to some degree the formation of blocking by localized topography.     

Kinetic equations and stationary energy spectra of weakly nonlinear internal gravity waves

An ensemble of random-phase internal gravity waves is considered in the dynamical framework of the Euler–Boussinesq equations. For flows with zero mean potential vorticity, a kinetic equation for the mean spectral energy density of the waves is obtained under hypothesis of Gaussian statistics with zero correlation length. Stationary scaling solutions of this equation are found for almost vertically propagating waves. The resulting spectra are anisotropic in vertical and horizontal wave numbers. For flows with small but non-zero mean potential vorticity, under the same statistical hypothesis applied to the wave part of the flow, it is shown that the vortex part and the wave part decouple. The vortex part obeys a limiting slow dynamics equation exhibiting vertical collapse and layering which may contaminate the wave-part spectra. Relation of these results to the in situ atmospheric measurements and previous work on oceanic gravity waves is discussed.     

On the transient adjustment of a mid-latitude abyssal ocean basin with realistic geometry: the constant depth limit

The early stages in the adjustment of a mid-latitude abyssal basin with realistic geometry are studied using an inverted one and one-half layer model of the Eastern Mediterranean Sea as a natural test basin. The model is forced with a localized sidewall mass source and a compensating distributed mass sink. A flat bottom basin is investigated for comparison with existing theories on abyssal gyral spin-up, and as a precursor to a study with realistic topography. As in existing theories, the early adjustment is dominated by sub-inertial Kelvin and Rossby waves. Obstacles and the varying coastal geometry do not impede the passage of the Kelvin wave, though the circuit time of the main Kelvin wave signal is reduced by an aggregate 6% for the abyssal Eastern Mediterranean basin. The scattering of the Kelvin wave due to small-scale variations in the coastline is also shown not to be significant to the adjustment. The relatively short period of time needed to reach a statistical steady state is attributed to western boundary current formation in response to local Kelvin wave dynamics. Upon cessation of the sidewall forcing, sub-inertial motion controls the spin-down adjustment with basin-scale Rossby waves becoming the most pronounced feature of the flow. Two dynamical issues of particular interest emerge in these simulations: the retardation of Kelvin wave propagation around the abyssal basin and the roles of detrainment and sidewall forcing in the interior vorticity balance. An idealized simulation using an elliptical basin is used to illustrate that the mechanism for Kelvin wave retardation is a geometrically induced dispersion due to large-scale variations in the coastline. A dynamical analysis of the interior circulation shows that detrainment alone does not develop a Sverdrup response. Both the localized sidewall injection and the detrainment are needed to describe the interior dynamics, with both poleward and equatorward flows developing during the adjustment.     

旋转大气中地形对涡旋自组织影响的初步研究

用一个带有地形项的β平面准地转正压涡度方程,进行2组积分时间长度为48h的试验,分析旋转大气中地形对多涡自组织的影响。地球旋转作用的引入主要会引起以下的差别：无旋转大气中,多涡自组织的特征是准终态涡将初始多涡全部吸收或全部组织起来;旋转大气中,多涡自组织的特征是准终态涡将初始多涡部分吸收或部分组织起来,差别较明显。中尺度地形对准终态涡位置的影响不同。无旋转大气中,中尺度地形对准终态涡位置的影响较小,有无地形的两个准终态涡中心之间的距离约100km;旋转大气中,中尺度地形对准终态涡位置的影响较大,有无地形的两个准终态涡中心之间的距离约200km,两者相差一倍左右。     

Rossby波的能量、能量通量与Lagrange函数

利用正压涡度方程计算波动能量通量时,它的形式将不同于直接利用运动方程所求得的通量,这是一个于六十年代初所提出的问题。在本文中,对此问题进行再次分析与研究。结果表明,如果将运动方程进行改写,使其包含了与涡度方程相等的条件,对于波动而言,就整个波动范围求平均且假定波动振幅为常数,则可得到相同的表示式。于文中,还利用此改写的运动方程,导得了波动位能的表示式,这为进一步研究非线性Rossby波提供了一个物理基础。     

ENERGY,ENERGY FLUX AND LAGRANGIAN OF ROSSBY WAVE

The energy flux derived from the barotropic vorticity equation differs from that obtained directly from the momentum equation.We re-study this problem raised in the early 1960s.The results show that if the momentum equation is rewritten in such a way that it contains the same conditions as that for the barotropic vorticity equation,then the same form of average energy flux can be obtained for the waves with constant amplitudes.With this new momentum equation,the potential energy of Rossby wave is derived and Lagrangian of nonlinear barotropic vorticity equation can be approximately found with this potential energy.This provides a physical basis for studying the dynamics of nonlinear Rossby wave with the approach of calculus of variation.     

用线性化全球原始方程谱模式研究地形强迫行星波垂直传播特征

本文用线性化全球原始方程谱模式来研究地形强迫行星波的垂直传播过程及演变特征.模式的积分结果表明:行星波的能量沿两支波导进行传播,在波从对流层向平流层传播中,极地波导起着主要作用.由于重力波破碎的阻尼作用,地形强迫的行星波无论它的波作用量或振幅都呈现振荡状态.     

Forced Rossby wave packets in barotropic shear flows with critical layers

In this paper, we investigate the meridional propagation of a forced Rossby wave packet towards a critical layer in a zonal shear flow by solving the linearized barotropic vorticity equation. The forcing is applied north of the critical layer. Two approaches are employed for solving this problem. First, an analytic solution valid for large time is derived, using Fourier and Laplace transform techniques and asymptotic approximations. This solution exhibits the modification due to the wave packet of the solution obtained by Warn and Warn (1976) [Warn, T., Warn H., 1976. On the development of a Rossby wave critical level. J. Atmos. Sci., 33, 2021–2024.] in the monochromatic case. A numerical investigation is then carried out using a finite difference scheme and a time-dependent radiation condition. It is found that the forced wave packet is absorbed at the critical layer and the total momentum transferred to the mean flow as a result of the absorption is observed to be proportional to the length scale of the wave packet. We also consider the case of a north–south mean flow with a longitudinally propagating wave packet forced to the east or west of the critical layer. The monochromatic version of this problem has been used before (Geisler, J.E., Dickinson, R.E., 1975. Critical level absorption of barotropic Rossby waves in a north–south flow. J. Geophys. Res., 80, 3805–3811.) to examine the interaction of western boundary currents and oceanic Rossby waves.     

热带风暴中波动特征的研究进展和问题

在分析热带风暴眼壁和螺旋雨带中尺度波动特征最新研究的基础上，指出这些研究所忽略的问题，其中包括重力惯性波和涡旋Rossby波波解存在的前提条件和约束、理论分析与观测研究存在的差异等。提出一种基于准平衡动力条件下，热带风暴内中尺度扰动涡散运动共存时，区别于标准模混合的不可分的混合涡旋Rossby-重力惯性波，并讨论了位涡守恒条件下这一类不可分混合波的可能成波机制。利用高分辨率的模式大气资料，采用非对称波分量的分解方法分析了Bonnie飓风中的中尺度波动特征，结果表明，热带风暴中1波型扰动既具有涡旋波性质，但也存在散度扰动的变化，而2波型扰动则体现了明显的不可分混合波的特性。     

台风麦莎的正压特征波动结构及其稳定性

利用中尺度WRF模式对2005年8月西北太平洋台风麦莎（Matsa）进行了精细的数值模拟。使用模式输出资料,对正压浅水方程组进行了数值差分计算,分析它在最大强度时刻的正压特征波动结构和稳定性。结果表明,台风麦莎内部包含有沿逆时针方向传播的重力惯性外波和涡旋Ross-by波,两种波动的结构和稳定性存在显著性差异。前者主要存在于台风外围,增长率随波长的减小而增加,台风外围的波动相速度为48．9～68．5m／s;后者主要位于距离台风中心200km内,表现为3波最不稳定,半径100km处相速度约为5m／s。此外,重力惯性外波的扰动风场与高度场基本相垂直,扰动散涡比值大于3倍,甚至达到10＾3倍,运动以辐合、辐散为主;涡旋Rossby波的扰动风场基本平行于高度场,扰动散涡比值为10＾-1～10＾-2,涡旋运动是其主要运动,与内螺旋雨带沿着切向圆周方向的传播具有密切关系。