地形对中尺度边界急流的影响

本文研究了两层流的浅水波模式,并考虑了地形的作用,当背景场为大尺度经向地转流υ_g时,在山地或海岸附近可以形成一类中尺度边界层急流,其特征宽度为Lc=L_0C_0/(υ_g+β_g~*/2f),式中 c_0=(g~*H)~(1/2),L_0=c_0/f为Rossby变形半径,β=-h_s/x为地形坡度。当地转流和山脉坡度满|υ_g+β_g~*/f|>c_0时,中尺度边界层急流中的惯性重力波可以产生超高速不稳定。对于向北的地转流(υ_g>0),山脉东坡有利于形成强而窄的边界层急流和出现超高速不稳定。对于向南的地转流(υ_g<0),在山脉的西坡也会出现同样的情形。     

华东中尺度地形对浙北暴雨影响的模拟研究

以一次梅雨降水为例，利用中尺度模式进行一系列中尺度地形对降水的增幅影响的敏感性试验。结果表明，中尺度地形对强降水区域的分布和强度有很大的影响，强降水中心位于地形附近，地形引起的１２小时降水增幅高达总降水的９０％以上；中尺度地形作为一种外界迫动，初始在低层形成气旋性辐合和水汽热量的集中，然后通过凝结潜热释放所造成的中高层增温和高层辐散，使得地形垂直环流加强和向上伸展。于是在降水、潜热释放与地形垂直环流之间出现一种正反馈机制，导致地形对降水的强烈增幅；同时午后下垫面加热所形成的不稳定层结也有利于地形垂直环流的不稳定发展，产生新的雨峰；初始场的中尺度扰动似乎在降水的地形性增幅中并不起明显作用。     

湖北省中尺度试验区地形对气象要素场的综合影响

本文分析了试验区特殊地形的热力、动力作用,得到了与地形尺度相当的平均意义下的地形风环流系统,揭露了它的演变规律及散度场的时空特点,发现地形风辐合场与试验区降水有关。最后讨论了试验区温压距平场的时空特征和试验区地形对气象要素场的综合影响。     

强地形有限区域中尺度数值模式在1995年汛期中的试用

陕西省的天气系统受地形的影响很大，因此选用了能准确处理陡峭地形的阶梯山脉坐标（η坐标）系建立强地形有限区域中尺度模式，克服了σ坐标系的缺陷，较准确地预告了陕西省的天气系统演变，对降水范围、落区和量级方面做出了难确的预报，揭示了陕西省暴雨的形成机制和演变规律。     

地形性中尺度环流的数值模拟及验证

建立了一个高分辨三维边界层诊断模式以模拟下垫面热力和动力的 非均匀性对边界层结构的影响。模式模拟了广东大亚湾核电站厂址区域（12 km×12 km） 47个典型天气系统下的地形性中尺度环流,其大坑的模拟风向、风速和温度与观测值 相比,风向差小于17.5#+[o]的概率为87.5%,风速比值在0.7～1.3之间的概率为72.9%, 温度差小于0.4#+[o]C的概率为72.9%。     

中尺度模式中的三维变量配置

由于中尺度模式中采用不同的三维变量配置,必将产生不同的预报和模拟效果.怎样的三维变量分布,才能产生最佳的模拟效果呢?一直没有人从事这方面的研究.为此,在线性非静力滞弹性方程组的基础上,从频率、水平群速和垂直群速方面将中尺度模式中常见的四种三维网格的计算频散性与解析解的情况进行了对比,主要采用图示比较的方法.结果表明:总的来看三维网格C/CP计算频散性能最好,Z/LZ和Z/LY网格次之,C/L网格最差.因此设计非静力斜压模式时,应尽量采用C/CP网格.但C/CP网格对水平波长较短的波,误差相对要大些.如果模拟的波动水平尺度较小时,为减少误差,水平格距要减小.另外C/CP网格主要用在有限差分模式中;要考虑谱模式中的变量配置时,应把C/CP网格和Z/LZ网格或Z/LY网格结合起来使用.     

复杂地形条件下三维多源浓度场模拟

目前，国内外使用的大气扩散模式很多，主要的是高斯模式及对它的各种订正形式。高斯模式的前提条件是污染物浓度符合正态分布，是适用于开阔平坦地形上的中小尺度模式：由于高新模式的局限性，对于复杂地形和复杂流场情况下的天气扩散问题，更多地采用烟团模式或K模式，     

一次华南暴雨的中尺度结构及复杂地形的影响

文中选取了 1998年 6月 8～ 9日的一次发生在华南的强降雨过程 ,利用观测资料和MM5中尺度模式对这个过程进行了诊断分析和数值模拟 ,研究了该暴雨过程的中尺度结构及华南地区复杂地形的影响。分析表明这次华南暴雨由锋面暴雨和暖区暴雨组成 ,具有不同的中尺度结构 ,其中广西梧州地区暴雨是准静止锋面上的中尺度对流系统造成 ,具有持续时间短 ,强度大的特征 ,MM5模拟的雷达回波强度超过 30dBz ,高度超过 2 0 0hPa ,并在其东、北侧出现闭合的次级垂直环流 ;珠江三角洲的暴雨是暖区暴雨 ,发生在深厚的暖湿气流内 ,85 0hPa上强度超过 16m/s的西南低空急流是影响降水的主要系统 ,该中心暴雨持续时间较长 ,降水强度也达到了暴雨标准 ,模拟雷达回波不明显 ,没有出现局地的次级环流。华南地区的复杂地形在这次华南暴雨过程中主要为动力性作用 ,具体表现在一支冷空气在低层由苗岭和南岭之间南下 ,南海上空一支暖湿气流北上直接到达梧州地区 ,另一支次暖湿空气在南岭的阻挡下由武夷山以南沿南岭和云开大山之间折而向西 ,这三支气流在梧州地区附近汇合 ,形成广西梧州地区的暴雨 ;同时南海上空北上的低层气流被迫向东北绕行海南岛 ,形成一个尺度为 2 0 0km左右的背风面气旋 ,这个气旋的东北部分加强了在珠江三角洲地     

中尺度地形对大气铅直运动和强降水的影响

本文概略地综述了关于地形（特别是中尺度地形）强迫在大气扰动的一些经典工作,它们都是由简化的理想情况引出的一些基本物理概念和原理,但这些知识有助于我们科学地去思考和解释那些更具体复杂的现象,文中还着重对地形扰动中的铅直运动作一些定性推论和讨论,因不它对强降水的触发,加强和持续有地接影响,此外还联系到长江流域的一些有关的观测现象和问题.     

夏季北京地区强地形雨中尺度结构分析

利用卫星、雷达资料,分析了2002年6月24日北京地区大暴雨的降水云团演变特征,结果表明：中α尺度对流系统减弱过程中经历了中β尺度云团的发展过程,中β尺度对流云团是北京西部局地暴雨的影响系统;在观测分析的基础上进行了数值模拟分析：低层东风气流向西移动遏太行山东坡辐合抬升,黄土高原低层偏西风向东移动,受太行山脉强迫倾斜上升,与太行山东坡的地形抬升叠加,在太行山及其东坡产生强烈的上升运动,并形成垂直次级环流圈,同时,低层的偏南气流在燕山南坡上升,而冷空气偏北气流在燕山南坡半山腰下沉,该次级环流圈是北京西部山区强降水产生和维持的主要物理机制。     

THREE-DIMENSIONAL MESOSCALE MODELING OF METEOROLOGICAL FIELDS OVER ZHUJIANG(PEARL)RIVER DELTA

The CSU-RAMS-2A was used to simulate the meteorological fields over the Zhujiang River Delta in South China.Initialized from a horizontally homogeneous atmosphere,real topography and inhomogeneous surface boundary condi-tions,the model was run with thermal and terrain forcing.The modeling results of winter and summer cases are com-pared with those observed.The similarity of the predicted distributions of winds,temperatures and humidities to the ob-served patterns permits us to conclude that the mesoscale distribution of meteorological elements for the two study datesis the result of the thermal and dynamical forcing by the underlying surface and topography.     

NUMERICAL SIMULATION OF MESOSCALE STRUCTURES OF TYPHOON AND OROGRAPHIC EFFECTS USING MM5*

The track,landfall,dynamic and thermodynamic and cloud-rain physical mesoscale structures and their evolution of typhoon HERB 1996 in 36 h from 0000 UTC 31 July to 1200 UTC 1 August 1996 were simulated by using the non-hydrostatic mesoscale model MM5.This period covered the process of typhoon HERB landfall at Taiwan and Fujian Provinces.Results show that the model successfully simulated the landfall process of typhoon HERB,revealed the most important characteristics of the mesoscale dynamic and thermodynamic and cloud-rain physical structure during its landfall.The simulated typhoon track was close to the observation.The center of cyclonic circulation simulated at 0000 UTC on 1 August 1996 (24 h integration) was located in shore near Fuqing,Fujian Province at which the typhoon was reported to landfall two hours later.It shows that strong upward motion formed by low level convergence existed in the eye-wall and subsidence at the eye.The wind field shows clear asymmetrical structure near the typhoon center.The cloud and rainband was screw-typed distributed around typhoon center,and consisted of meso-β scale rain cores.During the period of typhoon HERB staying near and passing over Taiwan,the lower cloud was developed in the eye region so that the previous clear typhoon eye on the satellite pictures became fuzzy.Observation shows that the typhoon center was "warm",but the model simulations with higher space resolution show that in the mid-troposphere the region of eye-wall with stronger upward motion and more cloud-and rain-water was warmer than the eye.During the period of typhoon passing over Taiwan and its following landfall at Fujian,the track of model typhoon deviated about 30 km northward (i.e.,rightward) because of the orographic effects of Taiwan Island,but the strength of the typhoon was not affected remarkably.The amount of rainfall on Taiwan in the 36 h simulations was enhanced more than six times by the orographic lifting of Taiwan Mountain.     

NUMERICAL STUDY OF OROGRAPHIC INFLUENCE ON LOW FREQUENCY OSCILLATION

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.     

IMPACT OF THE INITIALIZATION ON MESOSCALE MODEL PREDICTION IN SOUTH CHINA

1 INTRODUCTIONThe initial state of the atmosphere is one of the keyfactors that affect the result of NWP. With thedevelopment of increasingly finer NWP, the quality ofinitial atmospheric state has been drawing more andmore attention[1-7]. GRAPES 3D- Var(G…     

华南地区中尺度模式预报的初值影响分析

基于GRAPES 3D-Vat同化系统,介绍了根据静力平衡关系由高度场的增量来计算温度场的增量的方法,并结合常规探空资料同化,针对影响华南地区的一次冷空气过程的个例,分析了常规观测资料对初始场的影响。采用GRAPES区域中尺度模式进行了控制试验和同化试验,观测资料的检验表明,资料同化对GRAPES中尺度模式预报有正面影响,初始时刻预报敏感性较大并且变化较快,靠近地面的低层预报敏感性较为复杂,常规探空资料对高层大气预报能力的提高相对于中低层较小。     

IMPACT OF THE INITIALIZATION ON MESOSCALE MODEL PREDICTION IN SOUTH CHINA

1 INTRODUCTION The initial state of the atmosphere is one of the key factors that affect the result of NWP. With the development of increasingly finer NWP, the quality of initial atmospheric state has been drawing more and more attention[1-7].     

中尺度数值模式的自适应网格设计

引进了自适应网格设计的方法。自适应网要生成行技术基础变分原理,所生成的网格具有光滑性、一定程度的正交性和机调节网格疏密程度的优点,这种新技术可任意加密局地网格,从而达到以较小的计算量获得较高的计算精度的目的。将自适应网格技术应用于ＭＭ４中,并用来模拟１９２年６月１４日这次大范围暴雨过程。结果表明,采用自适应网格后计算稳定,２４ｈ降水预报得到明显改善。     

DESIGN OF A THREE-DIMENSIONAL GLOBAL ADIABATIC SPECTRAL PRIMITIVE EQUATION MODEL

A three-dimensional(3D)global adiabatic spectral primitive equation model has beendesigned.The main features are as follows.(1)Adoption of spherical harmonics and Tschebyscheff polynomials as the basis functions inthe horizontal and vertical respectively,but the unknowns in the spectral equations are two-dimensional;(2)Inclusion of the tropopause,which may vary with time and space;(3)Suggestion of a spectral method for representing the vertical structure of the atmosphereapplicable to the unsmoothed profile case;(4)In consideration of nonlinear vertical aliasing a technique is proposed to avoid it andnonlinear computational instability.Based on real data forecasts up to 48 hours have been performed.The results show that thestatistical verifications with the model are superior on the average to those with the T42L9 usedoperationally before 1995 at NMC of China at the same mean resolution.