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1.
The relationship between the quasi-stationary planetary waves forced by topography and heat sourceduring the Northern Hemisphere winter is investigated by means of a quasi-geostrophic,34-level,sphericalcoordinate model with the Rayleigh friction,the Newtonian cooling and the horizontal eddy thermal diffu-sion.The calculated results show that when the basic flow is the westerly in the tropical stratosphere,theamplitude of quasi-stationary planetary wave for zonal wavenumber 2 at middle and high latitudes is largerduring the Northern Hemispheric winter;while when the basic flow is the easterly,it is smaller.This is inagreement with the observed results.The calculated results also show that influence of the basic flow in the tropical troposphere on the quasi-stationary planetary waves is larger than that of the basic flow in the tropical stratosphere on the quasi-stationary planetary waves.  相似文献   

2.
Time-mean global general circulation data are employed to analyze the temporal and spatial variations ofthe meridional gradient of zonal mean potential vorticity,the critical wavenumber n_s for horizontal wave-propagation,and the critical wavenumber K_c for vertical wave-propagation.Thereby the kinematic charac-teristics in the propagation of atmospheric stationary waves and their annual variations are studied.Resultsshow that in the troposphere n_s and K_c usually decrease with the increase of either latitude or altitude.Synoptic and near-resonant Rossby waves could be trapped during their upward and meridional propagations.These characteristics possess prominent annual variations,especially in the Northern Hemisphere.It is foundthat the spatial and temporal variations of these kinematic characteristics are in good agreement with those ofthe atmospheric wave patterns.  相似文献   

3.
A zonal-vertical two-dimensional equatorial model is used to study the possibility that the long period oscillation of the zonal mean flow occurring in the lower equatorial stratosphere (QBO) is caused by local thermal ac-tivities at the tropical tropopause. The model successfully reproduces QBO-like oscillations of the zonal mean flow, suggesting that the local heating or cooling at the tropical tropopause is probably the main reason of QBO’s genera-tion. The analysis of the dependence of the oscillation on the wave fencing indicates that the oscillation is not sensible to the forcing scale. The model can reproduce QBO-like oscillations with any forcing scale if the fencing period and amplitude take appropriate values, proving that the internal gravity waves generated by local thermal source take much important roles in QBO.  相似文献   

4.
The distribution of troughs and ridges of geopotential height,the teleconnection patterns and the propagation pat-terns of stationary waves are the main features of the January mean geopotential height field at 500hPa.Data analysesand numerical experiments indicate that these three characteristics are associated to one another and closely related tothe mechanical forcing of the Rocky Mountains and Tibetan Plateau.There exists a prominent negative correlation inthe intensity variation between the American trough and the Asian trough at high and middle latitudes.Such negativecorrelation,in connection with the interannual variation of the intensity of the jets in front of the two troughs,leads tothe existence of similar teleconnection patterns in North America and East Asia.On the other hand,the different propa-gation behaviour of quasi-stationary waves downstream of the two main mountains results in a fundamental differencein the distribution of correlation chains in North America and East Asia.  相似文献   

5.
Using 1958-2002 NCEPNCAR reanalysis data, we investigate stationary and transient planetary wave propagation and its role in wave-mean flow interaction which influences the state of the polar vortex (PV) in the stratosphere in Northern Hemisphere (NH) winter. This is done by analyzing the Eliassen-Palm (E-P) flux and its divergence. We find that the stationary and transient waves propagate upward and equatorward in NH winter, with stronger upward propagation of stationary waves from the troposphere to the stratosphere, and stronger equatorward propagation of transient waves from mid-latitudes to the subtropics in the troposphere. Stationary waves exhibit more upward propagation in the polar stratosphere during the weak polar vortex regime (WVR) than during the strong polar vortex regime (SVR). On the other hand, transient waves have more upward propagation during SVR than during WVR in the subpolar stratosphere, with a domain of low frequency waves. With different paths of upward propagation, both stationary and transient waves contribute to the maintenance of the observed stratospheric PV regimes in NH winter.  相似文献   

6.
A nonlinear steady-state baroclinic primitive-equation numerical model of atmospheric forced stationarywaves is used to investigate the tropics-extratropics interactions.Newtonian cooling,Rayleigh friction andbiharmonic horizontal diffusion are included in the model.The Eliassen-Palm (EP) cross-section and three-dimensional wave activity flux,which was derived by Plumb (1985) for linear quasi-geostrophic stationarywaves on a zonal flow,are used as diagnostics for the vertical and horizontal propagation of the waves.Results of the numerical experiments and diagnostics analyses suggest that the extratropical influenceon the tropical large-scale motion is important.The mid-latitude orographic forcing,especially of the Qing-hai-Xizang Plateau,and the extratropical thermal forcing make substantial contribution to the main-tenance of the cyclonic circulation over the eastern tropical and subtropical Pacific as well as the inversecirculation over the western Pacific in the upper troposphere.In addition,the longitudinal variation ofdiabatic heating in tropics has a significant influence on the wintertime stationary waves at higher latitudes.  相似文献   

7.
Orographic effects on monthly-and seasonal-scale low frequency oscillation are investiged in terms of a five-level global spectral model with a triangle truncation at wavenumber 10 that contains relatively full physical parameterization, followed by analysis and comparison of the lowpass filtered data separately obtained from models with and without orography. Results show that remarkable seasonal characteristics are displayed in the orographic forcing-generated low frequency wavetrain on monthly and seasonal scales. It is found that the Northern Hemisphere summer orography-produced tropical heating acts as source of the low-frequency wavetrain for both hemispheres. Besides, the simulations indicate that the orographic wavetrain perturbation can give rise to the anomaly in the equatorial zonal flow, whose transient forcing will cause a new wavetrain in the Southern Hemisphere, thus completing the cross-equatorial propagation of the northern wave in interhemispheric action.  相似文献   

8.
An analysis is made of the effects of topography on the summer atmospheric energetics of the Northern Hemisphere in a low-resolution global spectral model. The numerical model is a global, spectral, primitive equation model with five equally spaced sigma levels in the vertical and triangular truncation at wavenumber 10 in the horizontal. The model includes comparatively full physical processes.Each term of the energy budget equations is calculated in four specific latitudinal belts (81.11°S-11.53°S; 11.53°S-11.53°N; 11.53°N-46.24°N; 46.24癗-81.ll癗) from a five-year simulation with mountains and a one-year simulation without mountains, respectively. Differences between them are compared and statistically tested. The results show that synoptical scale waves transport available potential energy and kinetic energy to long waves and increase conversion from available potential energy of the zonal flow to eddy's and from the eddy kinetic energy to the zonal kinetic energy in region 3 (11.53°N-46.24°N  相似文献   

9.
In a general baroclinic atmosphere,when the basic state includes meridional circulation,the sta-tionary waves might not only pass through the equatorial easterlies,but also strengthen significantly.The orographic forcing in the Northern Hemisphere mid-latitude might cause marked responses in thelow latitude atmosphere.This suggests that the meridional circulation plays an important role in theconnection of stationary responses in mid and low latitudes,and so does the heating forcing in theNorthern Hemisphere mid-latitude.Forced by the heating forcing in the Northern Hemisphere mid-latitude,the features similar to the Northern Hemisphere summer monsoon circulation can be ob-tained.It appears that the meridional circulation plays certain role in the formation of summer mon-soon circulation.The heating anomaly forcing located at the eastern equatorial Pacific makes the sta-tionary waves present PNA(Pacific-North America)pattern in the winter hemisphere,but it doesnot in the summer hemisphere.It suggests that the meridional circulation has a marked influence onthe route of stationary wave propagation both in the winter and summer hemispheres.  相似文献   

10.
The three-dimensional propagations of the forced stationary planetary waves in a realistic summer current, in which the vertical and horizontal wind shears are included, are discussed by using the refractive index squared of waves in a spherical coordinate system.The results show that there is no polar wave guide in stationary planetary wave propagations in summer. Thus, stationary planetary waves cannot propagate into the stratosphere. However, there are a wave guide pointing from the subtropics toward middle and high latitudes in the troposphere and another wave guide pointing from the lower troposphere at middle latitudes toward the upper troposphere near 30°oN in the forced stationary planetary wave propagations.A linearized, steady-state, quasi-geostrophic 34-level spherical coordinate model with Rayleigh friction and Newtonian cooling, horizontal kinematic thermal diffusivity is used to simulate the wave guides of three-dimensional propagations of stationary planetary waves in summer.  相似文献   

11.
In this paper, five-year simulated data from a low-resolution global spectral model with triangular trunca-lion at wavenumber 10 are analyzed in order to study dynamical features and propagation characteristics ofintraseasonal oxillations over the mid-latitudes and the tropical atmosphere. The simulations show that thereis the 30-50 day periodic oscillation in the low-resolution spectral model without non-seasonal external forcing,and spatial scale of the intraseasonal oscihations is of the globe .Further analysis finds that propagation charac-ters of intraseasonal oscillations over the mid-latitudes and the tropics are different. The 30-50 day oscillationover the tropics exhibits structure of the velocity potential wave with wavenumber 1 in the latitudinal and thecharacter of the traveling wave eastward at speed of 8 longitudes/day. However, the 30-50 day oscillationsin mid-latitude atmosphere exhibit phase and amplitude oscillation of the standing planetary waves and theyare related to transform of teleconnection patterns over the mid-latitudes. The energy is not only transferredbetween the tropics and the middle-high latitudes, but also between different regions over the tropics. Based on the analysis of 5-year band pass filtered data from a 5-layer global spectral model of Jow-ordetwith truncated wavenumber l0,investigation is done of the source of intraseasonal oscillations in the extratropicalmodel atmosphere and its mechanism. Results show that (1) the convective heat transferred eastward alongthe equator serves as the source of the intraseasonal oxillation both in the tropical and the extratropical atmos--phere; (2) the velocity-potential wave of a zonal structure of wavenumber 1 gives rise to oxillation in divergentand convergent wind fields of a dipole-form as seen from the equatorial Indian Ocean to the western Pacificduring its eastward propagation, thus indicating the oscillation in the dipole-form heat soure:e/sink pattertl; (3)the tropical heat-source oscillation is responsible for the variation in phase and intensity of the extratropicalstationary wave train, and the interaction between the oscillating low-frequency inertial gravity and stationaryRossby modes that are probably mechanisms for the oscillations ip the middle-high latitudes.  相似文献   

12.
In correspondence with the establishment of the“upper high and lower high”pressure pattern due to the activitiesof 500 hPa high over the Tibetan Plateau in summer,a series of changes of the East Asia atmospheric circulation willtake place.In this paper,the distributions of divergence and vertical velocity of 500 hPa high,the evolutions of atmos-pheric heat source,the variations of vorticity and zonal wind at 100 hPa level and vertical meridional cell over theTibetan Plateau etc.are statistically analyzed.Thus,we can see that the ascending motion and the convective heatingover the Tibetan Plateau,the South Asia high and the westerly jet on the north of the Plateau at 100 hPa level are weak-ened.The northern branch and the southern branch of the easterly jet on the south of the Plateau merge into a singlewhole and situate on the south of the former northern branch.In the meantime,thermodynamic land-sea discrepancy inSouth Asia and the convective heating over the Bay of Bengal is enhanced.It will play an important role in the mainte-nance of the easterly jet and the South Asia monsoon.  相似文献   

13.
It is proposed that the orographic stationary waves are required by long-term balance of momentum in the atmosphere with zonally asymmetric orographic forcing. This hypothesis may be confirmed successfully with the theoretical model of geostrophic waves. In the Part I, we will explain the observed phase distributions of orographic stationary waves at middle and high latitudes of the Northern Hemisphere, according to the long-term balance of zonal momentum over the stationary orographic forcing. It is revealed that the geographic distribution of stationary waves depends not only on local topgraphy but also on mean circulation fields and angular momentum flux in the atmosphere. So these waves cannot be simulated by the models in a restricted area.  相似文献   

14.
The process of stratospheric sudden warmings from development of planetary waves to.the sudden cooling after reversal of mean zonal circulation will be studied with the primitive equations of heat and momentum balances. It will be explained that the sudden warmings may occur only in the polar regions of winter stratosphere where zonal mean temperature decreases poleward. The heating rate in the order of major warmings is produced by developed planetary waves in the stratospheric breaking layers. The particular perturbation structure characterized by large amplitude of wave 1 together with minimum of wave 2 discovered by Labitzke (1977) is crucial for initiation of major warmings. The cooling by the same mechanism can be produced in the regions with reversed mean temperature gradient.  相似文献   

15.
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   

16.
The impacts of stratospheric initial conditions and vertical resolution on the stratosphere by raising the model top, refining the vertical resolution, and the assimilation of operationally available observations, including conventional and satellite observations, on continental U.S. winter short-range weather forecasting, were investigated in this study. The initial and predicted wind and temperature profiles were analyzed against conventional observations. Generally, the initial wind and temperature bias profiles were better adjusted when a higher model top and refined vertical resolution were used. Negative impacts were also observed in both the initial wind and temperature profiles, over the lower troposphere. Different from the results by only raising the model top, the assimilation of operationally available observations led to significant improvements in both the troposphere and stratosphere initial conditions when a higher top was used. Predictions made with the adjusted stratospheric initial conditions and refined vertical resolutions showed generally better forecasting skill. The major improvements caused by raising the model top with refined vertical resolution, as well as those caused by data assimilation, were in both cases located in the tropopause and lower stratosphere. Negative impacts were also observed, in the predicted near surface wind and lower-tropospheric temperature. These negative impacts were related to the uncertainties caused by more stratospheric information, as well as to some physical processes. A case study shows that when we raise the model top, put more vertical layers in stratosphere and apply data assimilation, the precipitation scores can be slightly improved. However, more analysis are needed due to uncertainties brought by data assimilation.  相似文献   

17.
Under semi-geostrophic approximation the nonlinear ordinary differential equations are obtained for the motion inthe barotropic and baroclinic atmospheres with the effects of zonal shear basic flow and topographic forcing included.Two constraints are acquired of finite-amplitude periodic and solitary waves in the original model with the aid of thephase-plane geometric qualitative theory of a dynamic system defined by the differential equation.The explicit solutionof the nonlinear waves is found by means of the approximation method and some significant results are achieved.  相似文献   

18.
Variations in wave energy and amplitude for Rossby waves are investigated by solving the wave energy equation for the quasigeostrophic barotropic potential vorticity model.The results suggest that compared with rays in the nondivergent barotropic model,rays in the divergent model can have enhanced meridional and zonal propagation,accompanied by a more dramatic variability in both wave energy and amplitude,which is caused by introducing the divergence effect of the free surface in the quasigeostrophic model.For rays propagating in a region enclosed by a turning latitude and a critical latitude,the wave energy approaches the maximum value inside the region,while the amplitude approaches the maximum at the turning latitude.Waves can develop when both the wave energy and amplitude increase.For rays propagating in a region enclosed by two turning latitudes,the wave energy approaches the minimum value at one turning latitude and the maximum value at the other latitude,while the total wavenumber approaches the maximum value inside the region.The resulting amplitude increases if the total wavenumber decreases or the wave energy increases more significantly and decreases if the total wavenumber increases or the wave energy decreases more significantly.The matched roles of the energy from the basic flow and the divergence of the group velocity contribute to the slightly oscillating wave energy,which causes a slightly oscillating amplitude as well as the slightly oscillating total wavenumber.  相似文献   

19.
A primitive equation model with a zonal domain and a p-σ incorporated vertical coordinate systemis used to study the effects of the envelope degree of orography on the simulated properties of bothwinter and summer climates.Results show that the orography with a larger envelope degree can im-prove the simulations to certain extent,especially in winter.It is found that the simulated propertiesof climate are mainly determined by the co-effects of the land-sea and the orographic distributions,and the envelope degree of orography has a secondary effect.However it should be taken properly inorder to improve simulations:otherwise,it would be harmful.Different envelope degrees of orogra-phy can be adopted in different areas.  相似文献   

20.
The mass stream function of zonal mean meridional circulation is calculated in terms of NCEP/NCAR monthly meridional wind speed and vertical velocity, and the climatic and anomalous features of zonal mean SST and meridional circulation are investigated. Results show that (1) a joint ascending branch of Northern and Southern Hadley circulation is on the side of the summer hemisphere near the equator ,being well consistent with the extremum of [SST ],and a strong descending by the winter-hemispheric side.(2)El Nino-related [SST] in low latitudes is an important outer-forcing source for anomaly meridional circulation, which is affected by seasonal variation of basic airflow and [SST ], and interannual and interdecadal changes of [SST] .  相似文献   

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