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1.
The contribution of thermal forcing to the planetary stationary waves will be studied also by assuming that heat balance in stationary waves over zonally asymmetric thermal forcing must be maintained over a long time period. Using the same model of geostrophic waves introduced in Part I, we may explain successfully the observed and simulated responses to the thermal forcing in the atmosphere, such as the wave 1 structure at high levels of middle latitudes, the seasonal changes of the stationary waves in the Northern Hemisphere, the opposite phase distributions of stationary waves at high and low levels of the subtropical regions in both hemispheres and so on.  相似文献   

2.
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   

3.
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   

4.
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   

5.
The wave rays and their seasonal variation of stationary and low-frequency Rossby waves are studied by using the Runge-Kutta scheme. The results show that for stationary waves the rays can reach lower latitudes in winter, and are limited in higher latitudes in summer. The main differences between the stationary and low-frequency wave rays are that low-frequency waves can propagate across the equator and the easterlies will not be an obstacle on their propagation. It explained to some extent the interaction of disturbances between the Northern and Southern Hemi-spheres. The lower wave frequencies and the stronger easterly flow are, the more difficult low-frequency waves will be to propagate across the equator. The waves with 20-day period are easier to propagate across the equator than that with 50-day period. The winter is the most favorable season for low-frequency waves to propagate into another hem-isphere.  相似文献   

6.
This study evaluates the seasonal cycle of the activity of convectively coupled equatorial waves(CCEWs),including mixed Rossby-gravity(MRG) and tropical depression-type(TD-type) waves,based on the twentieth century experiments of 18 global climate models(GCMs) from the Coupled Model Intercomparison Project phase 3(CMIP3).The ensemble result of the 18 GCMs shows that the observed seasonal cycle of MRG and TD-type wave activity cannot be well reproduced.The seasonal transition of wave activity from the southern hemisphere to the northern hemisphere is delayed from April in the observations to May in the simulations,indicating that the simulated active season of tropical waves in the northern hemisphere is delayed and shortened.This delayed seasonal transition of tropical wave activity is associated with a delayed seasonal transition of simulated mean precipitation.The mean precipitation in April and May shows a double-ITCZ problem,and the horizontal resolution is important to the delayed seasonal transition of wave activity.Because of the coincident seasonal cycle of MRG and TD-type wave activity and tropical cyclone(TC) geneses,the delayed seasonal transition of wave activity may imply a similar problem of TC genesis in the GCMs,namely,a delayed and shortened TC season in the northern hemisphere.  相似文献   

7.
In this paper, the concept of stationary-wave nonstationarity is presented and elucidated in the framework of the Lorenz circulation decomposition. This concept indicates the relative magnitude of the zonal nonuniform abnormity to the intensity of stationary waves on the monthly mean scale. Based on the Lorenz circulation decomposition, the nonstationarity degree Ius(Ilus) of the global (local) stationary waves is defined, and then used to analyze the stationary-wave nonstationarity at 30° 60°N, where the intensity of stationary waves at 500 hPa in the Northern Hemisphere, as is well known, is very high. The following findings are obtained: (1) There exist seasonal southward and northward movements in the position of the nonstationarity zones of the global stationary waves. The steady stationary waves occur in midlatitudes (35°-55°N) in winter and in the subtropical region (south of 35°N) in summer, associated with the major troughs over East Asia and North America and the weak European trough in winter, and with the relatively steady subtropical high system in summer. A high value center of Ius is at 35°N in spring and 50°N in summer, which might be caused by the seasonal variation of stationary-wave intensity, particularly in association with the interannual variability of trough ridge positions of stationary waves on the monthly mean maps. (2) There exists obvious asymmetry in Ilus, with the steady zones always located in the areas controlled by strong troughs/ridges and the unsteady ones in the areas where the stationary-wave intensity is low. The Ilus in the subtropics (south of 35°N) is larger in winter than in summer, and vice versa in the midlatitude region (north of 35°N). The summertime distribution of Ilus on the whole shows a rather complicated structure. However, North Europe is the most unsteady area for local stationary waves, as represented by high values of Ilus in both summer and winter, while over the North American continent (about 120°E-60°W), the °Ilus is slightly less than 1 in summer, indicating that the stationary waves in this region are more steady than those over other mid and high latitude regions. (3) From North China to Northwest Pacific, there is a high value zone of Ilus in summer, with its center (45°N, 130°E) located in the east of Heilongjiang Province. This influences the summer climate of northern China, including Northeast, North, and Northwest China. It is obvious that the nonstationarity is an intrinsic attribute of stationary waves, and can be regarded as being of the same importance as the intensity and energy-spectrum structure of stationary waves in the studies of the general circulation system.  相似文献   

8.
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   

9.
In this paper, the nonlinear stationary waves forced by topography and diabatic heating are investigated. It is pointed out that (1) the nonlinear interaction of different stationary waves forced only by topography might form dipole blocking in the atmosphere, this might explain the dipole blocking appeared in the Pacific and Atlantic regions; (2) the dipole blocking could not be caused by the nonlinear interaction of the different stationary waves forced by the diabatic heating alone; (3) the nonlinear interaction of the diffferent stationary waves forced by both topography and diabatic heating could initiate dipole blocking in the atmosphere. In winter, the dipole blocking mainly occurs in the west regions of the Pacific and the Atlantic, and the heat source over the western part of the two oceans is advantageous to the formation of dipole blocking in the west of two oceans. However, in summer, the dipole blocking could be formed in the east part of the two oceans, and the heat source over the eastern  相似文献   

10.
A two-level,quasi-geostrophic long-wave model based on spherical coordinates was developed with theexplicit part belonging to a low-order model.However,it includes not only diabatic heating,Ekman fric-tion and mountain distribution,but also parameterized forcing effects of transfer properties of transienteddies.Experiment results showed that,due to the introduction of the parameterization of transfer propertiesof transient eddies,remarkable improvements on characters of low-order model had been obtained.Inaddition to its economization in calculation and conciseness in physics as in a low-order model,the long-wave model was shown to describe the energetics and angular momentum balance of the atmosphere much morereasonably,and to present the features of zonal mean westerlies and stationary waves much more correctlythan the corresponding low-order model.This kind of long-wave model was therefore regarded as suitablefor theoretical research and numerical modelling of some aspects of the general circulation of the atmosphere.  相似文献   

11.
    
The wave rays and their seasonal variation of stationary and low-frequency Rossby waves are studied by using the Runge—Kutta scheme. The results show that for stationary waves the rays can reach lower latitudes in winter, and are limited in higher latitudes in summer. The main differences between the stationary and low-frequency wave rays are that low—frequency waves can propagate across the equator and the easterlies will not be an obstacle on their propagation. It explained to some extent the interaction of disturbances between the Northern and Southern Hemispheres. The lower wave frequencies and the stronger easterly flow are, the more difficult low—frequency waves will be to propagate across the equator. The waves with 20-day period are easier to propagate across the equator than that with 50—day period. The winter is the most favorable season for low—frequency waves to propagate into another hemisphere.  相似文献   

12.
Summary The role of stationary (monthly mean) and transient (departure from monthly mean) waves within the atmospheric energy cycle is examined using global analyses from the European Centre for Medium Range Weather Forecasts (ECMWF) for the period 1980–1987. Only January and July averages are considered.It is confirmed that planetary stationary waves are basically baroclinic. Their contribution to the globally averaged energy cycle of the atmosphere is comparable to that of the transient waves. In January they contribute about 40% to the baroclinic conversion (CA) from zonal mean to eddy available potential energy. Local values for the northern hemisphere even show a predominant role of the stationary wave conversions over those originating from transient waves. Part of the available potential energy of stationary waves (A SE) is converted to kinetic energy by warm air rising and cold air sinking. Nonlinear energy conversion, which can be interpreted as destruction of stationary temperature waves by transients, is the second sink forA SE. The order of magnitude of these two processes is similar.Barotropic nonlinear conversions, though negligible in the global average, reveal large conversion rates between the mean positions of the polar and the subtropical jets. Their orientation is suggestive of a tendency to increase stationary wave kinetic energyK SE at its local minimum between the jets at the expense of the synoptic scale transients.While all terms of the energy cycle related to stationary waves reveal a predominance of the planetary scale (zonal wave numbers 1–3) transient waves are governed by synoptic scale waves (zonal wave numbers 4–9) only with respect to the baroclinic and barotropic conversions: a significant amount of transient wave energy (50% for the global average ofA TE) is due to planetary scale waves.With 15 Figures  相似文献   

13.
Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes. However, considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes. To better understand such atmospheric teleconnection, several theories of wave energy propagation are reviewed in this paper: (1) great circle theory, which reveals the characteristics of Rossby waves propagating in the spherical atmosphere; (2) westerly duct theory, which suggests a “corridor” through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere; (3) energy accumulation-wave emanation theory, which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes; (4) equatorial wave expansion theory, which further explains the physical mechanisms involved in the interaction between the tropics and extratropics; and (5) meridional basic flow theory, which argues that stationary waves can propagate across the tropical easterlies under certain conditions. In addition, the progress made in diagnosing wave-flow interaction, particularly for Rossby waves, inertial-gravity waves, and Kelvin waves, is also reviewed. The meridional propagation of atmospheric energy exhibits significant annual and interannual variations, closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs, amongst others.  相似文献   

14.
While organized tropical convection is a well-known source of extratropical planetary waves, state-of-the-art climate models still show serious deficiencies in simulating accurately the atmospheric response to tropical sea surface temperature (SST) anomalies and the associated teleconnections. In the present study, the remote influence of the tropical atmospheric circulation is evaluated in ensembles of global boreal summer simulations in which the Arpege-Climat atmospheric General Circulation Model (GCM) is nudged towards 6-h reanalyses. The nudging is applied either in the whole tropical band or in a regional summer monsoon domain. Sensitivity tests to the experimental design are first conducted using prescribed climatological SST. They show that the tropical relaxation does not improve the zonal mean extratropical climatology but does lead to a significantly improved representation of the mid-latitude stationary waves in both hemispheres. Low-pass filtering of the relaxation fields has no major effect on the model response, suggesting that high-frequency tropical variability is not responsible for extratropical biases. Dividing the nudging strength by a factor 10 only decreases the magnitude of the response. Model errors in each monsoon domain contribute to deficiencies in the model??s mid-latitude climatology, although an exaggerated large-scale subsidence in the central equatorial Pacific appears as the main source of errors for the representation of stationary waves in the Arpege-Climat model. Case studies are then conducted using either climatological or observed SST. The focus is first on summer 2003 characterized by a strong and persistent anticyclonic anomaly over western Europe. This pattern is more realistic in nudging experiments than in simulations only driven by observed SST, especially when the nudging domain is centred over Central America. Other case studies also show a significant tropical forcing of the summer mid-latitude stationary waves and suggest a weak influence of prescribed observed SST in the northern extratropics. Results therefore indicate that improving the tropical divergent circulation and its response to tropical SST anomalies remains a key issue for increasing the skill of extratropical seasonal predictions, not only in the winter hemisphere but also in the boreal summer hemisphere where the prediction of heatwave and drought likelihood is expected to become an important challenge with increasing concentrations of greenhouse gases.  相似文献   

15.
用60 a Hadley气候中心的月平均海温资料,用EOF分析重构了4月份印度洋海温的一致变化型异常,并以此驱动IAP9层大气环流模式,分别研究了海温异常初期适应阶段、异常当月和气候平均夏季3种时间尺度下大气高度场响应的传播和分布特征.研究发现,初期适应阶段,高度场响应的垂直传播约需4d,且受控于整层无辐散约束;冷暖位相高度响应的水平传播路径差异较大,表现出明显的非对称性.海温异常当月,冷位相会激发出全球纬向Rossby波;而暖位相则激发出两半球洋面上2个大圆波列,且均有显著正压性.对气候平均夏季的北半球冷相位,高度响应表现为太平洋上空的3条异常纬带;对暖相位则表现为太平洋和大西洋上空的2个大圆波列.而南半球的高度场对冷位相响应主要表现为2波结构的绕极驻波,暖相位激发出环球的同心异常纬带.  相似文献   

16.
大气能量传播及不同纬度间大气相互作用的研究进展   总被引:1,自引:0,他引:1  
早期的理论分析认为大气中临界纬度的存在使得热带-热带外的大气活动互不影响。然而,大量的观测事实表明中低纬度大气运动存在着明显的动力联系。为了帮助人们更好地理解大气中的遥相关现象,在大量文献的基础上,综述了几种波能量传播理论:(1) 大圆理论指出了罗斯贝波在球形大气中的传播特征;(2) 西风通道理论发现了中纬度瞬变扰动越赤道传播的“走廊”;(3) 能量堆积-波列发射理论揭示了热带扰动影响到更高纬度大气活动的可能过程;(4) 赤道波侧向膨胀理论则利用转折纬度的概念更进一步解释了这种中低纬度大气相互作用的物理机制;(5) 经向基本流理论则认为在一定的条件下定常波可以穿过热带东风带传播到另一半球。此外,文中还回顾了在波-流相互作用诊断方面的研究进展,尤其是关于罗斯贝波、惯性重力波和赤道开尔文波。大气能量的经向传播具有显著的年变化和年际变化,这与ENSO、西风急流、大洋中部槽等的变化密切相关。  相似文献   

17.
The contribution of thermal forcing to the planetary stationary waves will be studied also by assuming that heat balance in stationary waves over zonally asymmetric thermal forcing must be maintained over a long time period. Us-ing the same model of geostrophic waves introduced in Part I, we may explain successfully the observed and simulated responses to the thermal forcing in the atmosphere, such as the wave 1 structure at high levels of middle latitudes, the seasonal changes of the stationary waves in the Northern Hemisphere, the opposite phase distributions of stationary waves at high and low levels of the subtropical regions in both hemispheres and so on.  相似文献   

18.
The coupled climate model EC-Earth2 is used to investigate the impact of direct radiative effects of aerosols on stationary waves in the northern hemisphere wintertime circulation. The direct effect of aerosols is simulated by introducing prescribed mixing ratios of different aerosol compounds representing pre-industrial and present-day conditions, no indirect effects are included. In the EC-Earth2 results, the surface temperature response is uncorrelated with the highly asymmetric aerosol radiative forcing pattern. Instead, the anomalous extratropical temperature field bears a strong resemblance to the aerosol-induced changes in the stationary-wave pattern. It is demonstrated that the main features of the wave pattern of EC-Earth2 can be replicated by a linear, baroclinic model forced with latent heat changes corresponding to the anomalous convective precipitation generated by EC-Earth2. The tropical latent heat release is an effective means of generating stationary wave trains that propagate into the extratropics. Hence, the results of the present study indicate that aerosol-induced convective precipitation anomalies govern the extratropical wave-field changes, and that the far-field temperature response dominates over local effects of aerosol radiative forcing.  相似文献   

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