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1.
文中利用一个半位势涡度时间不变式对热带斜压大气地转适应过程中的尺度准则进行了研究。结果表明 :对深厚系统而言 ,只要初始扰动的纬圈特征尺度足够大 ,则不论其初始扰动的经圈特征尺度多大 ,适应后的压力场的变化都很大 ,而纬圈流几乎维持不变 ,压力场向纬圈流适应 ;至于浅薄系统 ,对纬圈和经圈特征尺度都很大的初始扰动而言 ,适应后的压力场易于维持 ,主要是纬圈流向压力场适应 ;但当初始扰动呈现出纬圈型扰动特征时 ,适应后的压力场变化也很大 ,压力场向纬圈流适应 相似文献
2.
热带大气半地转适应理论的尺度分析和物理机制 总被引：1，自引：1，他引：1
对热带大气行星尺度运动所做的尺度分析和物理分析表明:热带大气 的行星尺度运动在y方向容易实现气压梯度力与Coriolis力的平衡，它称为纬圈的 半地转运动。半地转平衡的建立过程，也就是半地转适应过程相对是很短暂的，它不需 要考虑f=β0y随y的变化，因而主要依靠惯性重力波为频散；而半地转平 衡建立后的演变过程相对是很缓慢的，它主要受Kelvin波和Rossby波控制。 相似文献
3.
南半球环状模事件的准地转调整过程分析 总被引：1，自引：0，他引：1
本文利用NCEP/NCAR逐日再分析资料,分析了南半球环状模（SAM）事件生命过程中的准地转调整过程.由于SAM沿纬圈的水平尺度远远大于临界尺度罗斯贝变形半径,因此要求纬向风场在地转调整过程向气压场适应以达到地转平衡.研究结果表明,在纬向平均环流中,异常Ferrel环流强度的变化超前于SAM强度变化约2/16位相,异常Ferrel环流能够通过超前的整层大气质量的经向输运,改变中高纬度的质量分布装状况,导致中、高纬度地区间的位势高度梯度异常变化,而中、高纬度地区间的位势高度梯度异常发生变化就意味着SAM强度和位相发生变化;而当SAM强度和位相发生改变后,即中、高纬度地区南北方向上的位势高度梯度发生变化后,可破坏中纬度地区纬向风场与位势高度场之间的地转平衡,产生地转偏差;地转偏差产生后,又可驱动经向散度风场,造成Ferrel环流异常的变化,由此形成一个自我内部循环调整过程. 相似文献
4.
In this paper, the adaptation process in low latitude atmosphere is discussed by means of a two-layer baroclinic model on the equator β plane, showing that the adaptation process in low latitude is mainly dominated by the internal inertial gravity waves. The initial ageostrophic energy is dispersed by the internal inertial gravity waves, and as a result, the geostrophic motion is obtained in zonal direction while the ageostro-phic motion maintains in meridional direction, which can be called semi-geostrophic balance in barotropic model as well as semi-thermal-wind balance in baroclinic model. The vertical motion is determined both by the distribution of the initial vertical motion and that of the initial vertical motion tendency, but it is unrelated to the initial potential vorticity. Finally, the motion tends to be horizontal. The discussion of the physical mechanism of the semi-thermal-wind balance in low latitude atmosphere shows that the achievement of the semi-thermal-wind balance is due to the adjustment between the stream field and the temperature field through the horizontal convergence and divergence which is related to the vertical motion excited by the internal inertial gravity waves. The terminal adaptation state obtained shows that the adaptation direction between the mean temperature field and the shear flow field is determined by the ratio of the scale of the initial ageostrophic disturbance to the scale of one character scale related to the baroclinic Rossby radius of deformation. The shear stream field adapts to the mean temperature field when the ratio is greater than 1, and the mean temperature field adapts to the shear stream field when the ratio is smaller than 1. 相似文献
5.
热带大气垂直环流对海表温度异常的响应——一个初步的理论分析 总被引：1，自引：0，他引：1
本文提出了一个β平面定常的线性二维模式,并考虑了海面边界层和赤道侧向边界层,讨论了热带海表温度异常对大气所产生的垂直环流——经向环流和纬向环流。结果表明:热带大洋东部(例如太平洋)海表温度比平均状态暖而西部较冷时,其上空经向环流(Hadley环流)比平均状态强,而纬向环流(如在太平洋上,称Walker环流)弱。相反,当热带大洋西部暖而东部冷时,经向环流减弱,纬向环流加强。这些是与观测事实比较一致的。 相似文献
6.
The Ekman momentum approximation and its application 总被引：3，自引：0，他引：3
In the boundary layer, the flow is basically an equilibrium of three forces: Coriolis, pressure gradient and frictional. This means that it is an Ekman flow while the basic flow in the free atmosphere is an equilibrium of two forces: Coriolis and pressure gradient, and is a geostrophic flow. Therefore, it is natural to try to modify the geostrophic momentum approximation in the free atmosphere to become an Ekman momentum approximation in the boundary layer. The physical explanation and foundation of the Ekman momentum approximation are discussed. 相似文献
7.
研究了气候海洋与大气的临界时间跨度及其非线性作用的大致结构。与预报的空间分辩率及系统的非线性强度相联系，气候大气和海洋的临界时间跨度可反映系统可预报的相对时间尺度。对于具有同样空间特征尺度的大气和海洋，海洋的最小临界时间跨度约是大气的9倍（可达数日至数十日）。一般（外源变化缓慢的）气候海洋与大气的一阶非线性越强，其临界时间跨度越小。气候海洋与大气非线性作用的大致结构是：通常与科里奥利力对流体运动的规范作用（如地转运动）有关，非线性作用随纬度增加而减弱。距平流场的切变结构及其沿经向与纬向上强度的比较直接改变气候大气和海洋的非线性作用（比如，向东的距平环流强度与经向环流强度相当时，非线性作用最强），较强的外部驱动（风应力和压弹梯度力）使非线性作用加大等等。 相似文献
8.
A DYNAMICAL ANALYSIS OF BASIC FACTORS OF LOW-FREQUENCY OSCILLATION IN THE TROPICAL ATMOSPHERE* 
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下载免费PDF全文 Based on dynamical characteristics of the tropical atmosphere,a mathematical model of low-frequency oscillation (LFO hereinafter) in low-latitudes has been developed.The analysis shows that the distributive features (shear of wind speed) of easterlies and westerlies in low-latitudes,the divergence and convergence of meridional and zonal flow,the vertical structure of diabatic heating and the Coriolis parameter f are the basic factors resulting in the LFO,while quasi-periodical baroclinity development or index cycle of westerly waves in middle-latitudes of the Southern Hemisphere is an external forcing to the LFO in the tropical atmosphere.The resonance on adequate condition makes LFO suddenly enhanced. 相似文献
9.
利用NCEP/NCAR月平均再分析资料，采用奇异值分解方法分析200 hPa纬向风场与东亚地表加热场的空间耦合变化特征，揭示影响东亚副热带西风急流位置及强度变化的加热关键区域。研究结果表明，冬季西太平洋黑潮暖流区是表面感热、潜热通量场的大值区，其加热强度主要影响东亚副热带西风急流的强度变化，当加热增强（减弱）时，急流加强（减弱）。热带和副热带地区地表加热的反相变化对应纬向风的整体一致变化，且影响关键区在热带地区， 这种耦合分布型主要体现为年代际的变化特征。夏季，海陆感热加热差异主要影响中低纬纬向风的变化，而影响急流位置南北移动的加热关键区位于阿拉伯海及印度半岛北部，这种加热分布体现感热的局地性变化，可能与高原大地形分布有关。由于夏季降水的不均匀性，潜热加热与200 hPa纬向风场的耦合关系较为复杂。通过分析加热异常年的环流形势差异发现，对流层中上层经向温差对地表加热场异常变化的响应是导致高层纬向风变化的原因，这种地面加热变化导致高层温度场及流场的响应可通过热力适应理论得到较好的解释。 相似文献
10.
ECMWF预报模式在不同地形方案下的系统误差检验 总被引：1，自引：0，他引：1
Wallace等的研究表明,由于引进了包络地形方案,欧洲中期天气预报中心(ECMWF)的中期天气预报有所改善。本文是上述工作的继续。所用的资料为原作者的数值试验结果。检验的对象包括纬向平均风场、温度场和经圈环流,及不同波数域中的涡旋和经圈环流对角动量的平均经向输送。结果表明,在冬季,包络地形方案对低纬地区的温度场和风场的预报略有改进,对总涡旋动量通量的模拟也较好。然而对天气尺度系统的预报和对热带对流及积云摩擦的参数化却有待更进一步改善。 相似文献
11.
Renellys C. Perez Verena Hormann Rick Lumpkin Peter Brandt William E. Johns Fabrice Hernandez Claudia Schmid Bernard Bourlès 《Climate Dynamics》2014,43(11):2943-2962
Ship-based acoustic Doppler current profiler (ADCP) velocity measurements collected by several major field programs in the tropical Atlantic are averaged and combined with estimates of the mean near-surface velocity derived from drifters and Argo float surface drifts (ADCP+D) to describe the mean cross-equatorial and vertical structure of the meridional currents along 23°W and 10°W. Data from moored ADCPs and fixed-depth current meters, a satellite-derived velocity product, and a global ocean reanalysis were additionally used to evaluate the mean ADCP+D meridional velocity. The dominant circulation features in the long-term mean ADCP+D meridional velocity in the upper 100 m are the tropical cells (TCs) located approximately between 5°S and 5°N, with near-surface poleward flow and subsurface equatorward flow that is stronger and shallower in the northern cell compared to the southern cell. The thickness of the surface limb of the TCs decreases and the northern cell is found to shift further south of the equator from the central to eastern tropical Atlantic. Analysis of two-season means estimated from the ship-based ADCP, near-surface drift, and moored velocity data, as well as the simulated fields, indicates that the maximum poleward velocity in the surface limb of the TCs intensifies during December–May along 23°W largely due to seasonal compensation between the geostrophic and ageostrophic (or wind-driven) components of the meridional velocity, whereas the maximum equatorward flow in the subsurface limb of the northern cell intensifies during June–November along both 23°W and 10°W due to the seasonality of the geostrophic meridional velocity. 相似文献
12.
Charles A. Lin 《大气与海洋》2013,51(2):143-157
Abstract Baroclinic instability of zonal flows with different latitudinal structures is examined, using a linear, quasi‐geostrophic two‐level ß‐plane model. The flows have different amounts of skew, with respect to the channel centre, at different vertical levels. The results are interpreted in terms of the instability of the baroclinic components of the zonal flows. Because of the presence of latitudinal asymmetries, a spectrum of meridional modes is generated in the perturbation. In general, the meridional spectrum has two peaks: a primary peak at the planetary basic flow scale, and a secondary peak near the radius of deformation. As neutral stability is approached, the latter scale becomes more important, i.e. there is a tendency for more small‐scale structure near neutral stability. The perturbation zonal scale is close to the radius of deformation. The eddy amplitudes and momentum fluxes are also examined. The case that best applies to the atmosphere is also discussed. 相似文献
13.
Scale analyses for long wave, zonal ultralong wave (with zonal scale of disturbance L1~104 km and meridional scale L2~103 km) and meridional ultralong wave (L1~103 km, L2~104 km) are carried out and a set of approximate equations suitable for the study of these waves in a dry tropical atmosphere is obtained. Under the condition of sheared basic current, frequency analyses for the equations are carried out. It is found that Rossby waves and gravity waves may be separated for n ≥ l where n is the meridional wave number, whereas for n = 0 and L1~1000 km, the mixed Rossby-gravity wave will appear. Hence it is confirmed that the above results of scale analyses are correct. The consistency be-tween frequency analysis and scale analysis is established.The effect of shear of basic current on the equatorial waves is to change their frequencies and phase velocities and hence their group velocities. It increases the velocity of westward travelling Rossby waves and inertia-gravity and mixed waves, but decelerates the eastward inertia-gravity waves and the Kelvin wave. The recently observed low-frequency equatorial ocean wave may be interpreted as an eastward Kelvin wave in a basic current with shear. 相似文献
14.
利用1951-2000年北太平洋海温和副高特征量资料，探讨夏半年副高与前期海温的关系，发现影响副高活动的海温关键区赤道东太平洋前期信息最明显，从前期秋季持续至春季都保持与夏半年各月副高强度、西伸脊点位置的高相关；ENS0事件的形成超前于副高强度的转折约半年时间；El Nino年副高持续偏强偏西，La Nina年则相反，脊线位置也有所反映，但不如强度与西伸显著。在此基础上进一步分析表明，福建雨季降水、副高强度与Nino 3区海温存在着大约相一致的年代际振荡与突变时间；雨季降水分布的异常直接受到副高活动的影响，而副高活动又明显受ENS0循环的制约，因而关注赤道东太平洋海温异常及ENS0信息对福建雨季降水分布趋势的预测旦有重要意义。 相似文献
15.
C. -Y. Li 《Theoretical and Applied Climatology》1996,55(1-4):121-127
Summary Based on analysis of ECMWF data (1981–1987) and numerical simulations using a general circulation model (GCM), a quasi-two-week (10–20 day) oscillation in the tropical atmosphere is studied in this paper. It is shown that the kinetic energy of the quasi-two-week oscillation is larger than that of the intraseasonal oscillation, and is another important low-frequency system in the tropical atmosphere. By comparing it with the intraseasonal oscillation, some obvious differences can be found. For example, the zonal scale of the quasi-two-week oscillation is dominated by perturbations with wavenumber 2–4; its vertical structure mainly shows barotropic features; the zonal propagation is basically westward; and its meridional and zonal components the same size.With 10 Figures 相似文献
16.
1INTRODUCTIONAsshowninobservationalfacts,theevolutionofElNi駉displaysastheamplitudeexpansionandmigrationofanomalousdisturbancesinair-seacouplingsystems.Theoreticaladdressofthephenomenonhasbeenattemptedfromtheaspectofcouplingdynamics.Theresultsshowthattheair-seainteractionsystemincludesakindofunstablemode,whichispropagatingindirectionsdeterminedbyfactorsgoverningSSTchanges.Withanair-seacouplingmodel,Lau[1]wasamongtheearliestpeoplewhodiscoveredunstablestationarywavemodesintheair-seaintera… 相似文献
17.
利用斜压两层模式研究了赤道平面近似下的低纬热带大气适应过程。指出低纬斜压大气适应过程主要受重力惯性内波控制。通过重力惯性内波对初始非地转能量的频散，使纬向运动达到地转平衡，而经向维持非地转运动，正压模式下称为半地转平衡，斜压模式下称为半热成风平衡。通过对垂直运动方程的求解，可知，垂直运动只与重力惯性内波相联系，其产生与初始斜压位涡度无关，而只与初始时刻的垂直运动和垂直运动倾向有关，半地转适应使运动趋向水平运动。讨论了半热成风平衡的建立及其物理机制，指出由于重力惯性内波激发出垂直运动，与垂直运动相联系的水平辐合辐散调整流场和温度场之间的关系，使温压场最终达到半热成风平衡。通过对适应过程终态的分析，指出平均温度场和切变流场之间的适应方向决定于初始非半地转扰动的尺度与斜压Ｒｏｓｓｂｙ变形半径有关的特征尺度的比值，当比值大于１时，切变流场向平均温度场适应；当比值小于１时，平均温度场向切变流场适应 相似文献
18.
本文利用地转动量近似,并假设气压场为定常的圆形涡旋和初始风场不满足四力平衡(气压梯度力、科里奥利力、湍流粘性力和半地转惯性力)的条件下,求解了正压边界层中风场向气压场调整的初边值问题,得到了一些初步结论。本工作为利用四力平衡下的风速分布来诊断预报边界层风场提供了理论依据。 相似文献
19.
Summary Through the use of a zonal balance model we investigate the properties of the tropical meridional circulation to a range of specified diabatic forcing fields for climatologically observed zonal winds. As in earlier studies, the solutions show that latent heat release away from the equator forces an asymmetric meridional circulation in response the anisotropy in the inertial stability parameter with respect to the meridional location of the forcing. The presence of strong zonal flows appears to play a relatively minor role in determining the magnitude and asymmetry of the meridional circulation, whereas the structure of the diabatic heating, particularly the meridional breadth, proves to be of much greater importance.A dynamic efficiency factor, which provides an analytic measure of the efficacy of diabatic heating at generating zonal kinetic energy, generally exhibits a meridionally symmetric structure except during Northern Hemisphere summer. This asymmetry gives rise to a pronounced sensitivity of zonal kinetic energy generation to the meridional location of ITCZ convection. Further examination of the flow pattern suggests that for zonal flows representative of those over the Indian Ocean during the Northern Hemisphere summer months, meridional displacements of the heating of less than 20° latitude can result in as much as an order of magnitude difference in the rate of kinetic energy generation. Solution of the balance system also implies the existence of a feedback mechanism, between zonally-organized convection and the energetics properties of the large-scale flow, that is highly sensitive to the meridional location of the convection.With 11 FiguresThe National Center for Atmospheric Research is sponsored by the National Science Foundation. 相似文献
20.
Vikram M Mehta 《Climate Dynamics》1991,6(1):49-65
Meridional, linear, and free modes of global, primitive-equation, ocean-atmosphere models were analyzed to see if they contain multi-year, especially decadal ( 10–30 years), oscillation time scale modes. A two-layer model of the global ocean and a two-level model of the global atmosphere were formulated. Both models were linearized around axially-symmetric basic states containing mean meridional circulations. The linearized perturbation system was solved as an eigenvalue problem. The operator matrix was discretized in the north-south direction with centered finite differences. Uncoupled, meridional modes of oscillation of the ocean and the atmosphere models were calculated. Calculations were performed at three grid spacings (5°, 2.5° and 1.25°) and for two types of basic states (symmetric and asymmetric). Uncoupled, free oceanic modes in the presence of mean meridional circulations have oscillation time scales ranging from two years to several centuries. Such low frequency meridional modes do not exist in the ocean model if there are no mean meridional circulations. A large number of oceanic modes are grouped around decadal oscillation time scales. All the oceanic modes have neutral growth rates. The spatial structures of some of the oceanic modes are comparable to observed spatial structures of sea surface temperature variations in the Pacific Ocean. Most years to decades variability of meridional modes of the ocean model is contained in tropical and midlatitude modes. Some oceanic modes with years to decades periods have standing oscillations in the tropics and poleward propagation of zonal velocity and layer thickness outside the tropics. Uncoupled, free atmospheric modes in the presence of mean meridional circulations have oscillation time scales ranging from a week to several decades. Such low-frequency meridional modes do not exist in the atmospere model if there are no mean meridional circulations. A large number of modes are grouped around intraseasonal time scales. Unlike the oceanic modes, the atmospheric modes are weakly unstable. Most of the intraseasonal variability of atmospheric modes is contained in tropical, midlatitude, and polar modes. Atmospheric modes with oscillation periods longer than about one year have global extent. Meridional ocean-atmospheric modes exist in the models wherever there are mean meridional circulations, i.e., tropical, midlatitude, polar, and global. Oceanic and atmospheric eigenvectors have symmetric (assymetric) latitudinal structures if their basic states are symmetric (asymmetric) around the equator. For both models, models calculated at coarser than 2.5° grid spacing do not accurately represent low-frequency variability. Scale analysis shows taht advection by tge basic state meridional velocities is the primary cause of the meridional oscillations on time scales longer than two years in the ocean model and longer than a few weeks in the atmosphere model. Meridional modes of the coupled ocean-atmosphere models are the subject of a subsequent paper.This paper was presented at the International Conference on Modelling of Global Climate Change and Variability, held in Hamburg 11–15 September 1989 under the auspices of the Meteorological Institute of the University of Hamburg and the Max Planck Institute for Meteorology. Guest Editor for these papers is Dr. L. Dümenil 相似文献