大气热力强迫和动力强迫的调配及平均经圈环流的仿真模拟

通过研究平均经围环流（ＭＭＣ）及其所受的内外强迫作用的相互配置，指出对ＭＭＣ的热力和动力强迫满足确定的调配率。这一调配率受大气内在的斜压性、静力稳定度及绝对涡度制约。利用辐射加热和凝结加热参数化方案，结合欧洲中期天气预报中心（ＥＣＭＷＦ）的分析资料，对１月份平均经围环流进行数值仿真模拟。结果表明，热带对流加热可以形成双层Ｈａｄｌｅｙ环流结构；涡动动量输送对双Ｈａｄｌｅｙ环流的形成也有一定影响。中高纬度的ＭＭＣ则主要由外动量强迫及大气的动量和热量输送特征决定。     

MODULATION OF ATMOSPHERIC THERMAL AND MECHANICAL FORCINGS AND NUMERICAL MODELING OF MEAN MERIDIONAL CIRCULATION

Upon investigating the relative locations of internal and external forcing and the resultant mean meridional circulation,it was found that thermal forcing and mechanical forcing for the formation of atmospheric mean meridional circulation are modulated by a certain ratio.This ratio is determined by the inherent baroclinity,static stability and absolute vorticity of the atmosphere.By employing a parameterization scheme for radiative heating and condensation heating,together with the analysisdata of the European Center for Medium-range Weather Forecasts,the mean meridional circulation for January wassimulated numerically.It was found that latent heat release in the tropics may result in the formation of double-layeredHadley circulation,so do the eddy momentum transfer processes.On the other hand,mean meridional circulations in extra-tropics are mainly determined by external momentum forcing and atmospheric properties of eddy momentum andheat transfer.     

Non—Acceleration theorem in a primitive equation system: I. Acceleration of zonal mean flow

Non-acceleration theorem in a primitive equation system is developed to investigate the influences of waves on the mean flow variation against external forcing. Numerical results show that mechanical forcing overwhelms thermal forcing in maintaining the mean flow in which the internal mechanical forcing associated with horizontal eddy flux of momentum plays the most important roles. Both internal forcing and external forcing are shown to be active and at the first place for the mean flow variations, whereas the forcing-induced mean meridional circulation is passive and secondary. It is also shown that the effects on mean flow of external mechanical forcing are concentrated in the lower troposphere, whereas those due to wave-mean flow interaction are more important in the upper troposphere. These act together and result in the vertically easterly shear in low latitudes and westerly shear in mid-latitudes. This verti-cal shear of mean flow is to some extent weakened by thermal forcing.     

A description of numerical antarctic circumpolar currents

A sequence of numerical calculations has been made for the equilibrium balances of eddies and mean currents in open and partially blocked, periodic channels. The physical model employed is a two-layer, quasigeostrophic, wind-driven one, with important bottom friction and weak lateral friction. The resolved eddies provide the interior fluxes of momentum and potential vorticity which allow the mean state to be a balanced one. The set of calculations does not provide a parameter study as such, but does provide examples of the influences of alternative physical processes and geometrical constraints. These alternatives include the presence or absence of a partial barrier across the channel, the length of the channel, the addition of a transient component to the wind-driving, and the addition of a topographic sill across the channel gap. Particular attention is focused upon the steadily driven general circulation of a β-plane channel, because of the structural simplicity of the solution. The results may be broadly summarized as follows. The eddies are generated by a baroclinic instability of the mean flow. They act to intensity the upper layer mean jet and mean cross-jet potential vorticity gradient (through eddy horizontal Reynolds stress and relative vorticity flux divergence, respectively) and to transfer downwards mean zonal momentum, energy, and potential vorticity gradient (through eddy interfacial pressure drag, vertical pressure work, and vortex stretching flux divergence, respectively). In the case of a zonally uniform channel, the meridional heat flux is found not to conform closely to previously proposed parameterizations. The presence of a partial meridional barrier and a topographic obstacle are found to strongly influence the equilibrium solution, while neither a change in the basin length nor the presence of a transient wind component appear to importantly alter the solution.     

北半球30 hPa环流春季转变过程的诊断研究

利用1965—1986年30 hPa逐日高度、温度资料和月平均臭氧资料，对环流的春季转变过程进行了诊断研究。结果表明:50°N以北极冠地区高度场涡动方差E指数小于4×104（dagpm）2的初日可以作为30 hPa自然天气季节进入春节的近拟度量；冬末至早春环流在压、温和经、纬向风场方面均有显著变化；定常和瞬变涡旋动量、热量通量和通量辐散（合）的时-空变化特征明显；春季转变早、迟两类情况下极区平流层热源——臭氧在经向、纬向和垂直分布方面呈现异常。     

Annual mean meridional energy transport modelled by a general circulation model for present and 2 × CO2 equilibrium climates

The meridional energy flux modelled by the Bureau of Meteorology Research Centre general circulation model is examined. It is divided into atmospheric and oceanic components, and the resolved atmospheric components in turn into mean and eddy circulations. Comparison with observations shows the modelled total planetary meridional energy transport to be low, but shows better agreement for the resolved atmospheric component alone. The overall patterns of the individual circulation and energy components of the model also agree well, although strengths and locations do show some discrepancies. The doubled CO₂ climate change is analyzed in terms of the changes in each of the circulation and energy components. It is found that the changes are the relatively small residual of larger, and generally opposing changes in sensible heat and potential energy fluxes. Despite the general decrease in poleward energy flux, the poleward latent heat flux is found to increase. The reduction in poleward transport is found to be dominated by changes in the mean meridional circulation at low southern latitudes, and changes in both mean circulations and eddy fluxes elsewhere.     

On the Forced Tangentially-Averaged Radial- Vertical Circulation within Vortices Part Ⅰ: Concepts and Equations

将Eliassen建立在平面等压柱坐标系中的径向环流强迫理论（用于研究在摩擦力和非绝热加热过程影响下的静止对称涡旋），推广应用到研究移动非对称气旋或反气旋的径向环流，导出了考虑地球曲面影响的准拉格朗日等压柱坐标系的切向平均径向环流诊断方程，并根据Eliassen的解析解所揭示的涡旋径向环流在涡旋演变中的作用，定 性地讨论了各种热力和动力的作用，这些热力和动力因子除了磨擦力和非绝热加热外，还有平均和涡动形式的惯性力，角动量平流（相当涡度平流），角动量的垂直对流，温度平流，温度的垂直对流（相当绝热加热）等。     

On deep mean flow generation mechanisms and the abyssal circulation of numerical model gyres

Mesoscale resolution ocean general circulation model (EGCM) experiments have been carried out under a variety of different model physical assumptions, and the different model systems often produce very different deep mean flow fields. The flat bottom, rectangular basin experiments exhibit two distinct types of deep mean flow, which are here called “corotating” and “counterrotating”. Counterrotating deep flow, in which two adjacent deep gyres, with circulation of opposite senses, underlie the upper ocean eastward jet and its recirculation, has been found only in models with adiabetic two-layer model physics. None of the more complex model systems exhibit counterrotating deep flows; this type of flow is apparently restricted to a particular range of forcing/dissipation parameter space and/or particular model physical assumptions.Since the deep flow in these EGCM systems is generally weak, geostrophic dynamics provides the basic deep flow interior balance and the mean vertical velocity field, through the lower layer vorticity equation, largely determines the deep interior flow. The dynamical constraints on the mean vertical velocity field introduced by different model physical equations are reviewed and the adiabatic quasi-geostrophic (QG) two-layer model system is shown to be strongly constrained in several respects. In particular, the idea that eddy and mean heat flux divergence (or “layer thickness flux divergence”) drive the mean vertical velocity does not generalize to more complicated dynamical systems in which there is the possibility of altering the mean vertical density profile and/or in which the horizontal flow can be divergent. As a consequence of the constraints, there can be no basin net vorticity input to the lower layer via vortex stretching in the QG system.Because of the adiabatic QG constraints and the particular parametric regime in which the published adiabatic QG EGCM experiments exist, a very plausible explanation can be found for the existence of the deep cyclonic circulation of the model subtropical gyre. It is this cyclonic circulation that causes these deep flows to differ so dramatically from those of the more physically complex model systems. Because all the published adiabatic QG experiments that have non-trivial deep flows exhibit the counterrotating behavior, and because available ocean data do not support the existence of such a gyre in the North Atlantic, it seems important to thoroughly understand the reasons for the existence or absence of the deep cyclonic circulations. If they are an invitable feature of adiabatic QG systems, these models may need to be treated with caution as tools for understanding the mean ocean circulation.     

The effect of a regional increase in ocean surface roughness on the tropospheric circulation: a GCM experiment

The sensitivity of the atmospheric circulation to an increase in ocean surface roughness in the Southern Hemisphere storm track is investigated in a paired general circulation model experiment. Such a change in sea roughness could be induced by ocean waves generated by storms. Two extended permanent-July runs are made. One with standard sea surface roughness, the other with ten times as a large surface roughness over open sea poleward of 40° S. The regional increase in ocean surface roughness significantly modifies the tropospheric circulation in the Southern Hemisphere. The strongest effect is the reduction of tropospheric winds (by 2 m/s or 10%) above the area with increased roughness. The poleward eddy momentum flux is reduced in the upper troposphere and the meridional eddy sensible heat flux is reduced in the lower troposphere. Zonal mean and eddy kinetic energy are consistently reduced.     

Heat balance and eddies in the Peru-Chile current system

The Peru-Chile current System (PCS) is a region of persistent biases in global climate models. It has strong coastal upwelling, alongshore boundary currents, and mesoscale eddies. These oceanic phenomena provide essential heat transport to maintain a cool oceanic surface underneath the prevalent atmospheric stratus cloud deck, through a combination of mean circulation and eddy flux. We demonstrate these behaviors in a regional, quasi-equilibrium oceanic model that adequately resolves the mesoscale eddies with climatological forcing. The key result is that the atmospheric heating is large (>50 W m^?2) over a substantial strip >500 km wide off the coast of Peru, and the balancing lateral oceanic flux is much larger than provided by the offshore Ekman flux alone. The atmospheric heating is weaker and the coastally influenced strip is narrower off Chile, but again the Ekman flux is not sufficient for heat balance. The eddy contribution to the oceanic flux is substantial. Analysis of eddy properties shows strong surface temperature fronts and associated large vorticity, especially off Peru. Cyclonic eddies moderately dominate the surface layer, and anticyclonic eddies, originating from the nearshore poleward Peru-Chile Undercurrent (PCUC), dominate the subsurface, especially off Chile. The sensitivity of the PCS heat balance to equatorial intra-seasonal oscillations is found to be small. We demonstrate that forcing the regional model with a representative, coarse-resolution global reanalysis wind product has dramatic and deleterious consequences for the oceanic circulation and climate heat balance, the eddy heat flux in particular.     

The physical effects of topography and heat sources on the formation and maintenance of the summer monsoon over Asia

The physical effects of topography and heat sources on the formation and maintenance of the summer mon-soon over Asia we discussed in this paper by using the transformed Eularian-mean equations and a quasigeostrophic 34-level spherical coordinate model.The computed results of the divergence of the E-P flux, the induced meridional circulation and the pertur-bation geostrophic wind speed induced by the forcing of topography and heat sources show that the diabatic heating effect over the Tibetan Plateau may play an important role for the formation and maintenance of the summer monsoon over Asia, which is much greater than the dynamical effect of topography.The computed results also show that, of the physical effects of topography and heat sources on the formation and maintenance of the summer monsoon over Asia, the effect of forced meridional circulation is larger than that of the divergence of E-P flux of the induced waves.     

Impacts of Increased SST Resolution on the North Pacific Storm Track in ERA-Interim

This study examines the artificial influence of increasing the SST resolution on the storm track over the North Pacific in ERA-Interim. Along with the mesoscale oceanic eddies and fronts resolved during the high-resolution-SST period, the low-level storm track strengthens northward, reaching more than 30% of the maximum values in the low-resolution-SST period after removing the influence of ENSO. The mesoscale structure firstly imprints on the marine atmospheric boundary layer, which then leads ...     

变形的经向环流变化方程及其在诊断阻塞高压形成中的应用

本文推导出可以用来讨论大尺度扰动强迫对平均经圈环流作用的变形平均经圈环流变化方程，并利用此方程对北半球冬季4次阻塞高压的形成进行了诊断分析。分析结果表明:由于波动对经圈环流的强迫作用，使高压脊的西部南风加强，而东部北风加强，从而有利于阻塞高压的形成。文中还分别分析了瞬变波及其低频瞬变波部分在阻塞高压形成中对经圈环流的强迫作用，并讨论了低频瞬变波强迫在太平洋和大西洋地区阻塞高压形成的地域差别。     

Analysis on the Interaction between Turbulence and Secondary Circulation of the Surface Layer at Jinta Oasis in Summer

The kinetic energy variations of mean flow and turbulence at three levels in the surface layer were calculated by using eddy covariance data from observations at Jinta oasis in 2005 summer.It is found that when the mean horizontal flow was stronger,the turbulent kinetic energy was increased at all levels,as well as the downward mean wind at the middle level.Since the mean vertical flow on the top and bottom were both negligible at that time,there was a secondary circulation with convergence in the upper half and divergence in the lower half of the column.After consideration of energy conversion,it was found that the interaction between turbulence and the secondary circulation caused the intensification of each other.The interaction reflected positive feedback between turbulence and the vertical shear of the mean flow.Turbulent sensible and latent heat flux anomaly were also analyzed.The results show that in both daytime and at night,when the surface layer turbulence was intensified as a result of strengthened mean flow,the sensible heat flux was decreased while the latent heat flux was increased.Both anomalous fluxes contributed to the cold island effect and the moisture island effect of the oasis.     

EFFECT OF THE THERMAL FORCING ON THE SECONDARY CIRCULATION OF TYPHOONS

A non-dimensional secondary circulation equation for typhoons has been derived and then 11-yr com-positing typhoon data were used to estimate the thermally forced secondary circulation.The main resultshave been obtained as follows:(1)The diabatic heating and Cu vertical heat mixing are major thermal forcing factors.They have thesame magnitude of order.(2)The effects of eddy flux and Cu horizontal mixing of heat are of minor im-portance.(3)Ekman pumping and Cu vertical heat mixing cooperatively work.This feedback process isfavorable for the enhancement of the secondary circulation of typhoons.     

热力强迫对台风次级环流的作用

本文利用无量纲的台风次级环流方程,用西太平洋地区11年的综合台风资料,计算了热力因子强迫的次级环流。通过计算,得到主要结论如下: 1.非绝热加热和积云热量垂直混合是主要的热力强迫因子,二者的作用具有同样量级。 2.热量的湍流涡旋通量及积云的热量水平输送作用都比较小。 3.Ekman抽吸与积云热量垂直混合是相互促进,共同发展的。有利于次级环流的增强。     

The East Asian Upper-Tropospheric Jet Streams and Associated Transient Eddy Activities Simulated by a Climate System Model BCC_CSM1.1

In this paper, major features of the upper-tropospheric jet streams simulated by a coupled Climate System Model BCC_CSM1.1 are evaluated through comparison with the NCEP/NCAR reanalysis. The jet streams consist of the East Asian subtropical jet (EASJ) and the East Asian polar-front jet (EAPJ). Associated stationary wave and synoptic-scale transient eddy activities (STEA) are also examined. The results show that the climatological positions of the westerly jet streams are well captured by BCC_CSM1.1, but with slight intensity biases. Statistics from the 6-h model outputs reveal that the jet core number (JCN) of ESPJ is significantly underestimated. Examination of the simulated seasonal evolution of the westerly jet stream indicates that the model has produced a westward movement of the EASJ core in May, one month earlier than that in the reanalysis. Analysis of stationary wave activities shows that the overestimated meridional wind component may have caused considerable enhancement of meridional momentum and heat transport. The stationary Rossby wave represented by the wave activity flux at the southern flank of the Tibetan Plateau is favorable to the growth of asymmetric zonal wind and the multiple-center pattern of JCN. Unlike the stationary wave heat flux transport, the model tends to systematically generate weaker transient heat flux over East Asia. Further analysis of STEA exhibits a general consistent pattern between the simulation and the reanalysis, while the intensity of the northern STEA branch associated with the EAPJ is greatly reduced. The deficiencies of eddy momentum and heat flux transport and accompanied eddy forcing may contribute to the biases of the simulated upper-tropospheric jet streams, suggesting the potential importance of midlatitude internal atmospheric dynamics in shaping the tropospheric general circulation, which is not yet fully and accurately resolved in the current BCC_CSM1.1.     

雷暴大风过程中对流层中低层动量通量和动能通量输送特征研究

2014年5月31日北京发生一次雷暴大风过程。以雷达资料同化结果为初始场,对此次过程进行高分辨率数值模拟。采用非静力平衡和非地转平衡的经向动量方程和质量权重动能方程,利用模拟资料,对雷暴大风过程中经向动量和质量权重动能进行收支分析,以此来研究雷暴过程中对流层中低层动量通量和动能通量输送特征,讨论地面大风的可能成因。分析结果表明,在对流层中低层,经向动量通量散度是影响经向动量局地变化的主要强迫项。雷暴系统后部的入流把中低层的经向动量倾斜向下输送,系统前部对流云区中低层的下沉气流也向下输送经向动量。这两支下传动量通量先后与近地面经向动量的水平通量汇合,向系统前沿输送经向动量。在北京西北部地形阻挡作用下,经向动量通量在系统前端近地面辐合,促进那里的经向动量局地增长,有利于增强那里的南风。质量动能收支的特征与经向动量收支类似,在近地面层质量动能的局地变化主要是由质量动能通量散度引起的。系统后部入流把中层质量动能向下传输到近地面层,然后与近地面质量动能的水平通量汇合,向系统前沿输送质量动能。相对来说,近地面层经向动量和质量动能的水平通量比下传通量更重要,这主要与低层较强的东南急流有关。     

ECMWF预报模式在不同地形方案下的系统误差检验

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。     

冬季格陵兰以东区域海冰与北太平洋风暴轴的关系

对45个冬季格陵兰以东区域海冰密集度场与北太平洋500 hPa位势高度滤波方差场作奇异值(SVD)分析.结果表明:SVD得到的第1对空间典型分布反映了冬季格陵兰以东区域海冰异常与北太平洋风暴轴异常变化密切相关.进一步的合成分析显示:海冰异常导致大气环流调整,气压梯度、急流、850 hPa天气尺度涡动热量经向通量和垂直通量、局地斜压性均发生改变,从而对北太平洋风暴轴的强度及中心位置位移造成影响.