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1.
Luo Zhexian 《Acta Meteorologica Sinica》1996,10(1):13-21
By using the linearized barotropic vorticity equation in polar coordinates the stability of perturbations on a large scale circular basic flow is transformed into a generalized eigenvalue problem,yielding the relationship between the growth rate of the amplitude of perturbations and the azimuthal wave number. Then, numerical experiments whose integration time is 60 model hours are performed in terms of a quasi-geostrophic barotropic model in Cartesian coordinates using the perturbation stream function field of unstable mode superimposed on a strong and weak circular basic flows as the initial fields. The experimental results reveal that the amplitudes of the initial perturbations in the model atmosphere grow with time. The amplitude of the perturbations superimposedon the strong circular basic flow grows quicker and forms a spiral-band-like structure. 相似文献
2.
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3.
G.R. Flierl V.D. Larichev J.C. McWilliams G.M. Reznik 《Dynamics of Atmospheres and Oceans》1980,5(1):1-41
We derive exact nonlinear solutions to the inviscid quasigeostrophic two-layer equations. The solutions represent isolated eddies with an amplitude that decays rapidly away from the eddy. They translate steadily either to the east (if there is a barotropic component in the fringes of the eddy) or either to the east or rapidly to the west (if the exterior field has only a baroclinic mode structure). They are strong in the sense that all of the fluid within a finite radius from the center is carried along with the eddy as it translates. The solutions have a characteristic north-south antisymmetry with the nonlinear vortex pair interactions being an essential feature of the dynamics. However, we also show that radially symmetric perturbations of a special form but arbitrary amplitude can be superimposed on the basic solutions; thus the antisymmetric structure may to some extent be masked. We show nondimensional dispersion relationships: atmospheric and oceanic planetary wave phenomena do fall in the range of parameters where theory predicts solitary eddy solutions can exist. 相似文献
4.
CHANGES OF TYPHOON INTENSITY AND ITS POSSIBLE INFLUENCING FACTORS IN AN f-PLANE BAROTROPIC QUASIGEOSTROPHIC MODEL 
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下载免费PDF全文 LUO Zhexian 《Acta Meteorologica Sinica》2004,18(1):73-86
By using an f-plane barotropic quasigeostrophic model with the grid-spacing being 5 km,21 experiments whose integration time is 36 h are performed in this paper in order to investigate interactions between a typhoon vortex and its adjacent mesoscale vortices.Results show that whether the interaction leads to the intensification of the typhoon vortex depends on two kinds of factors:one is the value of the maximum wind speed of the typhoon vortex and the intensity of the shearing of circular basic flow:and the other is the condition of mesoscale vortices in the shearing basic flow,such as the spatial distribution,scale,intensity and structure of mesoscale vortices. There is the nonlinear relation between typhoon intensity and the scale and intensity of initial mesoscale vortices. 相似文献
5.
《Dynamics of Atmospheres and Oceans》1999,29(2-4):335-364
Stochastic wind forcing of ocean gyre circulations is examined using the ideas of generalized linear stability theory applied to the barotropic vorticity equation of a idealized ocean. The barotropic vorticity equation is linearized about a time-evolving basic state flow, and the spatial patterns of stochastic surface wind stress curl that are optimal for increasing the variability of the ocean are computed. The most disruptive pattern of stochastic forcing is found to be insensitive to: measures of variance, the optimization time, the temporal decorrelation time of the stochastic forcing, the time evolution of the basic state flow, the stability of the basic state flow, basin size, gyre symmetry, and the presence of bathymetry. In addition, the most disruptive pattern of wind stress curl is reminiscent of that which would be associated with individual large-scale weather systems in the atmosphere, and changes in the amplitude of the atmospheric teleconnection patterns. The response of a nonlinear model to stochastic forcing described by the optimal patterns is examined, and the dynamics of the response discussed. 相似文献
6.
On stochastic stability of regional ocean models to finite-amplitude perturbations of initial conditions 总被引：1，自引：0，他引：1
We consider error propagation near an unstable equilibrium state (classified as an unstable focus) for spatially uncorrelated and correlated finite-amplitude initial perturbations using short- (up to several weeks) and intermediate (up to 2 months) range forecast ensembles produced by a barotropic regional ocean model. An ensemble of initial perturbations is generated by the Latin Hypercube design strategy, and its optimal size is estimated through the Kullback–Liebler distance (the relative entropy). Although the ocean model is simple, the prediction error (PE) demonstrates non-trivial behavior similar to that existing in 3D ocean circulation models. In particular, in the limit of zero horizontal viscosity, the PE at first decays with time for all scales due to dissipation caused by non-linear bottom friction, and then grows faster than (quasi)-exponentially. Statistics of a prediction time scale (the irreversible predictability time (IPT)) quickly depart from Gaussian (the linear predictability regime) and becomes Weibullian (the non-linear predictability regime) as amplitude of initial perturbations grows. A transition from linear to non-linear predictability is clearly detected by the specific behavior of IPT variance. A new analytical formula for the model predictability horizon is introduced and applied to estimate the limit of predictability for the ocean model. 相似文献
7.
最敏感扰动的演变与夏季乌拉尔地区的持续性异常环流 总被引：1，自引：1，他引：0
通过数值实验对初始扰动不稳定发展建立异常环流型的过程进行了分析。选择了东亚夏季风异常的１９９１年和１９８５年两个典型年份的平均环流作为基流,以共轭敏感性分析得到的最敏感扰动作为初始扰动,分析其在不同的环流背景下的发展情况。结果说明,１９９１年欧亚地区的基流不稳定性较强,且初始扰动结构有利扰动发展,因而通过能量频散在乌拉尔地区激发扰动并强烈发展,建立起阻塞形势。而１９８５年的扰动在乌拉尔地区形成正涡度距平,不利于阻高的建立。从而导致１９９１年和１９８５年夏季乌拉尔地区几乎相反的异常环流。一系列对比实验说明,异常环流型的建立,不仅依靠能量的频散,更依靠扰动通过正压不稳定过程从基流吸收能量而发展。它既有赖于基流自身的不稳定,又取决于初始扰动的结构以及相对于基流的位置。基流选择了具有特定结构的初始扰动型,只要在有利位置上给予扰动,就能够激发出扰动波列,建立强的持续异常环流型。不论初始波列的位相在一定范围内如何改变,扰动总是倾向于在基流的特定不稳定区域发展。 相似文献
8.
利用线性化的两层正压原始方程模型，对有水平和垂直切变基流的圆形涡旋中螺旋波的不稳定作了研究。结果表明，当基流失稳时，涡旋中不稳定扰动的厚度场、速度场在上、下两层都具有明显的螺旋结构，下层的螺旋结构要较上层复杂。基流垂直切变越大则越易失稳。失稳时上、下层扰动的配置接近反位相，故该螺旋波结构相应于斜压模。此时螺旋波上的扰动中心在切向是逆基流传播的，在径向则基本没有传播，而螺旋臂的整体运动缓慢。失稳的螺旋波其散度场要较涡度场明显，物理量的配置也大体符合重力惯性波的情况，故可认为其是重力惯性波的不稳定所致。本模型中该螺旋波的形态与实际热带气旋中的螺旋云(雨)带很相象。 相似文献
9.
Optimal Perturbations Triggering Weather Regime Transitions: Onset of Blocking and Strong Zonal Flow 总被引：1，自引：0，他引：1
In this paper, the approach proposed by Mu and Jiang (2008) to obtain the optimal perturbations for triggering blocking (BL) onset is generalized to seek the optimal perturbations triggering onset of the strong zonal flow (SZF) regime. The BL and SZF regimes are characterized by the same dipole-like anomaly pattern superposed on the climatological flow, but with opposite sign. The results show that this method is also superior at finding the initial optimal perturbations triggering onset of the SZF regime, especially in the medium range. Furthermore, by comparing the two kinds of conditional nonlinear optimal perturbations (CNOPs) trig-gering onset of BL and SZF regimes, we find that in the linear approximation, there is symmetry in the sensitivities for BL and SZF onset, and the perturbations that optimally trigger onset of BL and SZF regimes at times when linear approximation is valid are also characterized by the same spatial pattern but with opposite sign. Whereas when the optimization time is extended to 6 days, the two kinds of CNOPs lose their out-of-phase behavior. The nonlinearity results in an asymmetry between the sensitivity for BL and SZF onset. Additionally, we find that the optimal perturbations have one common property, which is that the second baroclinic mode contributes more to the initial perturbations while the barotropic mode dominates the final structures. 相似文献
10.
The impact of nonlinear stability and instability on the validity of the tangent linear model 总被引：10，自引：0，他引：10
l.Intr0ducti0nTheequationsgoverningthemotionsoftheatmosphereandoceanaren0nlinear0nes.Itisdiffcultandcomplicatedtodealwiththenonlinearproblem.Sothetangentlinearmodel(TLM),whichisobtainedbylinearizingthenonlinearmodelinthevicinityofthebasicflow.iswidelyutilizedinthetheoreticalresearchandpracticalimplementationintheatmosphericandoceanicsciences.First-TLMcanbeusedtoestimatetheev0luti0nofsmallPerturbati0nsinaf0recastmodel.Second,itisadoptedinextendedKalmanfilterinthedataassimilation(Evensen,l99… 相似文献
11.
设计了一个热带赤道β-平面的两层海洋模式,在准长波近似下,应用最大截断模分析赤道波的基本形态,指出无论是正压模或斜压模Kelvin波、Rossby波及基本流所对应的“地形Rossby波”是最基本的波系,在基本流的一定切变条件下,它们之间可以耦合出一类不稳定波。在浅混合层近似和“快波近似”下,正压模和斜压模是可以分离的,因此可以分别分析它们的色散特征,由于它们的特征量不同,在同样波长(扰动的纬向尺度)下,扰动的增长率也不同,通过分析得出在一定参数下,斜压模扰动增长率为正压模的2倍。近似分析表明,混合层中流场的增长要快于温跃层,但温跃层的温度增长要比混合层明显。 相似文献
12.
With the aid of a global barotropic model, the role of the interaction of the synoptic-scale disturbance and the planetary flow in block onset is examined by a 4-dimensional variational approach. A cost function is defined to measure the squared errors of the forecasted stream functions during block onset period (day 4 and day 5 in this study) over a selected blocking domain. The sensitivity of block onset with respect to the initial synoptic-scale disturbance is studied by examining the gradient of the defined cost function with respect to the initial (during the first 24 hours) vorticity forcing, which is evaluated by the adjoint integration. Furthermore, the calculated cost function and gradient are connected with the limited-memory quasi-Newton optimization algorithm for solving the optimal initial vorticity forcing for block onset. For two studied cases of block onset (northern Atlantic and northern Pacific) introducing the optimal initial vorticity forcing, the nonlinear barotropic advection process mostly reconstructs these blocking onset processes. The results show that the formation of blocking can be correctly described by a barotropic nonlinear advection process, in which the wave- (synoptic-scale) flow (planetary-scale) interaction plays a very important role. On an appropriate planetary-scale flow, a certain synoptic-scale disturbance can cause the blocking onset by the interaction between the synoptic scale perturbations and the planetary scale basic flows. The extended forecasts show that the introduction of the optimal initial vorticity forcing can predict the blocking process up to the 7th or 8th day in this simple model case. The experimental results in this study show that the 4-dimensional variational approach has a good potential to be applied to study the dynamics of the medium-range weather processes. This simple model case study is only an initial trial. Applying the framework in this study to a complex model will further our understanding of the mechanism of the atmospheric/oceanic processes and improve their prediction. 相似文献
13.
Charles A. Lin 《Dynamics of Atmospheres and Oceans》1985,9(1):1-16
Baroclinic instability of a zonal flow with latitudinal structure is examined using a nonlinear quasi-geostrophic, two-level β-plane model. An initially small perturbation with the structure of the linearly most unstable mode is allowed to grow to finite amplitude through nonlinear interaction. Because of latitudinal asymmetries of the basic zonal flow, a spectrum of meridional modes is generated in the perturbation. The time evolution of zonal wind and perturbation meridional structures, and their Fourier meridional mode spectra are examined. The radius of deformation is an important meridional scale in both the zonal flow and perturbation. This is especially true during the barotropic decay phase of the baroclinic wave. Time series of energy conversion terms show there is no energy accumulation. 相似文献
14.
Lu Weisong 《Acta Meteorologica Sinica》1989,3(1):90-97
Based on a non-frictional and non-divergent nonlinear barotropic vorticity equation and its solutions oftravelling waves,the criteria for linear and nonlinear barotropic instability are gained respectively at an equilibriumpoint of the equation on a phase plane.The linear and nonlinear analytical solutions to instability waves arealso found.The computational results show that if their amplitudes are equal at the initial time,the amplitudeincrements of nonlinear instable barotropic wave are always less than those of linear instable barotropic wave.The nonlinear effects can slow down the exponential growth of linear instability.The time needed for makingthe amplitude double that of initial time by instabilities,is about 6h for linear instability and about 18h fornonlinear instability,the latter is in agreement with the observations in the real atmosphere. 相似文献
15.
关于西风急流在强迫扰动中作用的数值试验 总被引：3，自引：2，他引：3
本文利用非线性水波方程谱模式模拟了不同基本气流对低纬和中纬地区涡源扰动的强迫响应，进而讨论西风急流在大尺度流场强迫扰动中的作用。试验分析表明，中纬度西风急流对来自低纬的扰动波列有增哟的阻 阻滞的作用，并能影响强迫扰动的波数和路径。在存在西风急流的情况下，基本气流对低纬扰源的响应比对中纬扰源的响应要强得多。 相似文献
16.
LUO Zhexian 《Acta Meteorologica Sinica》2004,18(2):179-194
By using an f-plane barotropic quasi geostrophic model in the rectangular coordinates with a grid spacing of 5 km,ten experiments whose integration time is 36 hours are performed in order to study the interaction between a typhoon vortex and a mesoscale vortex whose initial center position is located at 2 rm northwest to the typhoon center,where rm is the radius of maximum wind of the typhoon vortex. Results show that the interaction can create a pair of smaller scale vortices or lumps,which extend from the outside region of the typhoon to near its center,resulting in the inward propagation of mesoscale vorticity.In this process,the vorticity concentration of the mesoscale vortex may appear.The coexistence of the propagation and the concentration makes the increase of vorticity in the inside region i.e.a more intensive typhoon.Meanwhile,the intensity of the lump with positive vorticity oscillates with time,with the oscillation period being several hours,the distance from the typhoon center to the lump center also has a similar oscillation period,which reduces the oscillation of typhoon intensity.In the case of stronger circular basic flow,the interaction can make the intensification of typhoon more obviously. In addition,in some parametric conditions,the interaction may break down the continuous vorticity zone,exhibiting a cluster of smaller vorticity lumps. 相似文献
17.
Abstract The topographic stability of forced planetary waves in α β‐channel is investigated using a barotropic model. The equilibrium forced waves are the result of the interaction of a constant mean zonal wind over finite‐amplitude surface orography. Small‐amplitude perturbations of the equilibrium flows are considered that have a wavy part with the same zonal wavenumber as the forcing but an arbitrary meridional structure. The mean zonal part of the perturbations is also taken to be arbitrary. This configuration allows us to (1) isolate those instabilities that depend crucially on topography through form drag and (2) investigate non‐topographic effects on topographic instability that arise from the convergence of Reynolds stresses. A numerical stability analysis is then performed wherein the effects of truncation are emphasized. This numerical approach casts doubts about the results obtained from some earlier studies involving various ad hoc assumptions. We find, in particular, that unstable long waves (i.e. waves with the zonal wavelength greater than the meridional wavelength) exist under superresonant conditions. This contradicts some previous results that suggest long waves are unstable only when the flow is subresonant. Further, our model reveals the existence of some interesting travelling instabilities. The latter are shown to depend on both form drag and Reynolds stresses in that these two mechanisms alternate in time in supplying the perturbation with the required energy to maintain the exponential growth. 相似文献
18.
Numerical experiments on forcing dissipation and heating response of dipole (unipole) are carried out using global spectral models with quasi-geostrophic barotropic vorticity equations. For each experiment model integration is run for 90 days on the condition of three-wave quasi-resonance. The results are given as follows: Under the effects of dipole (unipole) forcing source and basic flow intensity, there exist strong interactions among the three planetary waves and quasi-biweekly and intraseasonal oscillation of the three planetary waves. In the meantime, the changes in the intensity of dipole or unipole forcing source and basic flow have different frequency modulation effects on LFO in the middle and higher latitudes. The results of the stream function field of three quasi-resonant waves evolving with time confirm that the low-frequency oscillation exists in extratropical latitude. 相似文献
19.
Stefano Pierini 《Dynamics of Atmospheres and Oceans》1985,9(3):273-280
In the framework of the equivalent barotropic dynamics, we show that the kinetic energy and enstrophy a small scale perturbation superimposed on a large scale solitary wave do not grow in time as long as the perturbation scale remains much less than that of the wave. This property is proved to hold for the equivalent modons of Flierl et al. which therefore turn out to be resistant to small scale perturbations. These conclusions appear to explain the numerical results of McWilliams et al. on non divergent modons. 相似文献
20.
Variations in Wave Energy and Amplitudes along the Energy Dispersion Paths of Nonstationary Barotropic Rossby Waves 总被引：1，自引：1，他引：0
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. 相似文献