一种减少有限区气象模式嵌套误差积累的方法

介绍了一种减少有限区气候模式中嵌套误差积累的新方法－三维嵌套方法，详细阐述了这种方法提出的原因，必要性和它的理论基础，在有限区气候模式上进行三维嵌套二维嵌套的对比试验，试验结果表明三维嵌套方案可减少嵌套预报误差的积累，并且对于降水的预报也有很大的改善。     

三维嵌套技术在有限区域模式长时间积分中的初步应用

在复杂地形条件嵌套细网格模式基础上, 利用球圈模式与有限区域模式自嵌套, 就三维嵌套方法在长时间积分中的模拟结果进行了初步分析。结果表明:三维嵌套对垂直层次选取较敏感; 在长时间积分中模式运行稳定, 积分时间越长, 其优势越明显。这为有限区气候模式侧边界方案提供了新的思路。     

区域气候模拟中侧边界嵌套误差的研究

在复杂地形条件下嵌套细网格模式的基础上，建立了与球圈模式相嵌套的区域模式系统，对几种不同条件下的嵌套误差进行了比较分析，研究了区域模式嵌套误差的特征分布及时空演变特征。初步分析表明:区域模式嵌套造成的误差在不同区域的分布不同，且不同的物理量在时空的分布也不同；动能场的误差主要在边界区上层的流入区，感热场的误差在边界区上层，水汽的误差在边界区上层的流入区；侧边界输入时间间隔对模式嵌套误差有一定的影响。有限区细网格模式在上层长波误差大于粗网格环圈模式上层误差，在下层短波模拟的误差比粗网格环圈模式的下层误差要小。相速误差对侧边界嵌套误差的影响在下层很严重，嵌套误差的大小与大小模式的网格距之比有关；在大小模式物理参数化过程一致的条件下，无日变化的区域模式其嵌套误差远大于有日变化的区域模式嵌套误差。     

一粗细网格模式“三维嵌套”方案的设计及试验结果分析

该文简要地分析了水平侧边界嵌套技术中存在的问题，提出了“三维嵌套”的设想，并就不同范围对水平侧边界嵌套及三维嵌套方案进行了对比试验。试验结果表明：（１）三维嵌套方案对区域模式的降水及中、下层形势场的预报均有所改进；（２）嵌套区域越小，三维嵌套方案对预报的改进效果越明显；（３）三维嵌套方案对预报的改进随积分时间的增长而愈加显著     

中尺度业务模式系统侧边界嵌套方法的研究

为提高预报准确率，在对多种嵌套方案试验对比的基础上，选用了一种计算效果较好，方法也不甚复杂的Ｄａｖｉｅｓ物理量松弛方案，对中尺度业务模式系统进行了预报试验。其网格边界值采用Ｔ４２Ｌ９谱模式的预报值。嵌套模式与原模式用同一个例进行了预报对比试验。结果表明，嵌套方案考虑了大尺度环流背景场在边界附近对中尺度系统的强迫作用，提高了有限区域模式的实际预报能力。     

MOMS中尺度模式侧边界嵌套方法的研究

由于中尺度模式网格格距小，为满足预报时效要求，又需节省计算机资源，一般计算区域不能太大，若在业务预报工业中，不采用嵌套方案，很难得到满意的预报效果。文章在对多种嵌套方案试验对比基础上，选用一种计算效果较好，方法也不甚复杂的Davies物理量松驰方案，对MOMS中尺度模式进行了预报试验，其四周网格边界值采用了国家气象中心的T42L9谱模式的预报值。嵌套模式与原模式用同一个例进行了预报对比试验。结果表明，嵌套方案考虑了大尺度环流背景场在边界附近对中尺度系统的强迫作用，提高了有限区域模式的实际预报能力。     

南海热带气旋数值预报模式与全球谱模式的嵌套试验

分析了各嵌套变量的作用和效果，发现采用部分变量嵌套就能取得一定效果，各变量的作用也不完全相同。这样，可以选取作用大，质量好，易处理的变量进行嵌套。并相应地提出了一个边界嵌套处理方案，应用于南海带热带气旋数值预报有限区模式（ＴＬ１０）与全球谐模式（Ｔ６３）的嵌套过程，通过数值预报试验，表明采用该嵌套处理方案能够取得良好的效果。     

有限区分析预报系统及其业务应用

中国国家气象中心在新开发的有限区多元最优插值分析技术及１５层球面网格原始方程模式的基础上建立了一个新的有限区分析预报系统。１９９１年投入业务使用，主要用于２４－４８ｈ降水预报。这个系统是依附于全球同化预报系统的一个分支系统。亦即使用全球谱模式６ｈ预报作为初估值进行有限区细网格分析及使用其１２—６０ｈ预报作为侧边界值进行非同步嵌套预报。作为一个升级模式系统，它的进步表现在：较充分使用了卫星测湿资料及地面资料的细网格多元最优插值分析；同时使用同场及质量场初值，成功地实现了有限区非线性正规模初始化处理；采用位涡拟能守恒差分格式，包含较真实地形的球面坐标原始方程模式；实现了具有不同模式地形的差分模式与谱模式的嵌套及设计了分级降水客观检验系统。     

异模式嵌套及中期降水数值预报的试验

成功地将一有限区域细网格模式嵌套在T63L9全球谱模式中，并利用该嵌套模式 做了降水中期数值预报的试验。结果表明，嵌套的细网格模式预报的中期降水明显地优于该谱模式，要做好中期降水预报，使用嵌套模式是必要的。     

论区域气候模式与全球模式嵌套时边界区的选择

做了3个试验,第一个试验只用大气环流模式(GCM),主要考察GCM的性能并确定其误差的区域分布.后两个为对比试验,一个试验中,将区域气候模式(RCM)(NjU-RCM)的侧边界放在全球模式(L9R15)中我们感兴趣的区域,未考虑侧边界区GCM的误差大小,另一个试验中,RCM的侧边界位置根据GCM预报误差的空间分布选取,使其落在GCM预报误差较小的区域.3个试验都对1998年5、6、7月份中国区域的降水过程进行了模拟和比较.结果表明:单独使用GCM的效果最差;当用GCM-RCM嵌套模式对区域气候进行预测时,GCM侧边界值的误差对RCM的模拟结果有显著的影响,嵌套侧边界若选择在GCM系统性误差较小的地区,模拟或预测效果会有明显的改进.     

Sonic Anemometer Tilt Correction Algorithms

The sensitivity of sonic anemometer-derived stress estimates to the tilt of the anemometer is investigated. The largest stress errors are shown to occur for unstable stratification (z/L<0) and deep convective boundary layers. Three methods for determining the tilt angles relative to a mean streamline coordinate system and for computing the tilt-corrected stresses are then compared. The most commonly used method, involving a double rotation of the anemometers' axes, is shown to result in significant run-to-run stress errors due to the sampling uncertainty of the mean vertical velocity. An alternative method, requiring a triple rotation of the anemometer axes, is shown to result in even greater run-to-run stress errors due to the combined sampling errors of the mean vertical velocity and the cross-wind stress. For measurements over the sea where the cross-stream stress is important, the double rotation method is shown to overestimate the surface stress, due to the uncorrected lateral tilt component. A third method, using a planar fit technique, isshown to reduce the run-to-run stress errors due to sampling effects, and provides an unbiased estimate of the lateral stress.     

Can added value be expected in RCM-simulated large scales?

Nested Limited-Area Models require driving data to define their lateral boundary conditions (LBC). The optimal choice of domain size and the repercussions of LBC errors on Regional Climate Model (RCM) simulations are important issues in dynamical downscaling work. The main objective of this paper is to investigate the effect of domain size, particularly on the larger scales, and to question whether an RCM, when run over very large domains, can actually improve the large scales compared to those of the driving data. This study is performed with a detailed atmospheric model in its global and regional configurations, using the “Imperfect Big-Brother” (IBB) protocol. The ERA-Interim reanalyses and five global simulations are used to drive RCM simulations for five winter seasons, on four domain sizes centred over the North American continent. Three variables are investigated: precipitation, specific humidity and zonal wind component. The results following the IBB protocol show that, when an RCM is driven by perfect LBC, its skill at reproducing the large scales decreases with increasing the domain of integration, but the errors remain small even for very large domains. On the other hand, when driven by LBC that contain errors, RCMs can bring some reduction of errors in large scales when very large domains are used. The improvement is found especially in the amplitude of patterns of both the stationary and the intra-seasonal transient components. When large errors are present in the LBC, however, these are only partly corrected by the RCM. Although results showed that an RCM can have some skill at improving imperfect large scales supplied as driving LBC, the main added value of an RCM is provided by its small scales and its skill to simulate extreme events, particularly for precipitation. Under the IBB protocol all RCM simulations were fairly skilful at reproducing small scales statistics, although the skill decreased with increasing LBC errors. Coarse-resolution model simulations have difficulties in simulating heavy precipitation events, and as a result their precipitation distributions are systematically shifted toward smaller intensity. Under the IBB protocol, all RCM simulations have distributions very similar to the reference field, being little affected by LBC errors, and no significant differences were found between the small scales statistics and the precipitation distributions obtained over different RCM domains.     

有限区域模式侧边界处理方案的比较试验

用中尺度模式（ＭＭ５）与国家气象中心全球谱模式相嵌套,比较了三种侧边界处理方案对１９９７年３月华东地区２７个测站地面要素预报质量的影响,发现不同侧边界条件对内域预报质量的影响存在一定的差异。     

Sources of systematic errors in the climatology of a regional climate model over Europe

 Two ten-year simulations made with a European regional climate model (RCM) are compared. They are driven by the same observed sea surface temperatures but use different lateral boundary forcing. For one simulation, RCM AMIP, this forcing is obtained from a standard integration of a global general circulation model (GCM AMIP), whereas for the other simulation, RCM ASSIM, it is derived from a time series of operational analyses. The archive of analysis fields (surface pressure plus winds and temperatures on various pressure levels) is not sufficiently comprehensive to provide directly the full set of driving fields required for the RCM (in particular, no moisture fields are present), so these are obtained via a GCM integration, GCM ASSIM, in which the model is continuously relaxed towards the analysis fields using a data assimilation technique. Errors in RCM AMIP can arise either from the internal RCM physics or from errors in the lateral boundary forcing inherited from GCM AMIP. Errors in RCM ASSIM can arise from the internal RCM physics or the boundary moisture forcing but not from the driving circulation. Although previous studies have considered RCM integrations driven either by output from standard GCM integrations or operational analyses, our study is the first to compare parallel integrations of each type. This allows the total systematic error in an RCM integration driven by standard GCM output to be partitioned into components arising from the driving circulation and the internal RCM physics. These components indicate the scope for reducing regional simulation biases by improving either the driving GCM or the RCM itself. The results relate mainly to elements of surface climate likely to be influenced by both the driving circulation and regional physical processes operating in the RCM. For cloud cover, errors are found to arise largely from the internal RCM physics. Values are too low despite a positive relative humidity bias, indicating shortcomings in the parametrisation scheme used to calculate cloud cover. In summer, surface temperature and precipitation errors are also explained principally by regional processes. For example excessive solar heating leads to anomalously high surface temperatures over southern Europe and excessive drying of the soil reduces precipitation in the south eastern sector of the domain. The lateral boundary forcing reduces precipitation in the south eastern sector of the domain. The lateral boundary forcing also exerts some influence, mainly via a tropospheric cold bias which partially offsets the warming over southern Europe and also increases precipitation. In other seasons the lateral boundary forcing and the regional physics both contribute significantly to the errors in surface temperature and precipitation. In winter the boundary forcing (apart from moisture) is responsible for about 60% of the total error variance for temperature and about 40% for precipitation, due to the cold bias and circulation errors such as a southward shift in the storm track. The remaining errors arise from the regional physics, although for precipitation an excessive supply of moisture from the lateral boundaries also contributes. The skill of the mesoscale component of the surface temperature and precipitation distributions exceeds previous estimates, due to more realistic observed climatology. The mesoscale patterns are very similar in the two RCM simulations indicating that errors in the simulation of fine scale detail arise mainly from inadequate representations of local forcings rather than errors in the large-scale circulation. Circulation errors in RCM AMIP (e.g. cold bias, southward shift of storm track) are also present in GCM AMIP, but are largely absent in RCM ASSIM except in summer. This confirms evidence from previous work that the key to reducing most circulation errors in the RCM lies in improving the driving GCM. Regional processes only make a major contribution to circulation errors in summer, when reduced advection from the boundaries allows errors in surface temperature to be transmitted more effectively into the troposphere. Finally, we find evidence of error balances in the GCM which act to minimise biases in important climatological variables. This reflects tuning of the model physics at GCM resolution. In order to achieve simultaneous optimisation of the RCM and GCM at widely differing resolutions it may be necessary to introduce explicit scale dependences into some aspects of the physics. Received: 17 September 1997/Accepted: 10 March 1998     

Theoretical Basis and Application of an Analogue- Dynamical Model in the Lorenz System

The theoretical basis and application of an analogue-dynamical model (ADM) in the Lorenz system is studied. The ADM can effectively combine statistical and dynamical methods in which the small disturbance of the current initial value superimposed on the historical analogue reference state can be regarded as a prediction objective. Primary analyses show that under the condition of appending disturbances in model parameters, the model errors of ADM are much smaller than those of the pure dynamical model (PDM). The characteristics of predictability on the ADM in the Lorenz system are analyzed in phase space by conducting case studies and global experiments. The results show that the ADM can quite effectively reduce prediction errors and prolong the valid time of the prediction in most situations in contrast to the PDM, but when model errors are considerably small, the latter will be superior to the former. To overcome such a problem, the multi-reference-state updating can be applied to introduce the information of multi-analogue and update analogue and can exhibit exciting performance in the ADM.     

A stable and accurate Davies-like relaxation procedure using multiple penalty terms for lateral boundary conditions

A lateral boundary treatment using summation-by-parts operators and simultaneous approximation terms is introduced. The method is similar to Davies relaxation technique used in the weather prediction community and have similar areas of application, but is also provably stable. In this paper, it is shown how this technique can be applied to the shallow water equations, and that it reduces the errors in the computational domain.     

持续性强降水的区域模式动力中期预报研究

持续性强降水及其次生灾害给人民的生产和生活造成严重影响, 延伸其模式动力预报能力对防灾、减灾具有重要意义。随着对持续性强降水过程形成机理及模式动力中期预报认识的不断提高, 以减小模式初始条件误差、边界条件误差以及内场预报误差为目标提出了一系列动力中期预报技术方法, 主要包括:针对边界条件提出低通滤波技术方案, 改进了5 d以上的环流及降水预报; 针对模式预报内场进行谱逼近技术试验, 对提前3—7 d的小雨以上量级的降水预报改进明显; 针对初始条件进行多尺度混合更新初值技术预报试验, 融合全球预报的大尺度场及区域模式预报的中小尺度场进行15 d预报, 明显提高了50及100 mm以上的持续性累积降水预报时效。      

我国西部高原大气边界层中的对流活动

利用 1 998年第 2次青藏高原野外试验中的多普勒声雷达探测、低空探测观测以及卫星观测资料对高原大气边界层内的对流现象进行分析研究。声雷达探测到了高原边界层内有强烈的对流活动。这种对流泡中心的垂直速度可超过 1m/s,并存在尺度为 1个多小时的周期性 ,表现为中小尺度的有组织的湍流活动。高原边界层强对流得以发展和维持的物理机制是 :强辐射加热、复杂的地形地貌形成的下垫面不均一性造成边界层斜压性、边界层内的平流活动等 ,这些现象都有利于对流的发展。在这些条件的作用下 ,边界层内可以产生一系列有组织的强湍流大涡旋活动 ,这些大涡旋形成的热泡在向上发展的过程中有的能够发生合并 ,变得更大也更为猛烈 ,达到凝结高度以上可形成对流云 ,并发生充分的对流混合。成云过程凝结潜热释放更有利于对流运动进一步发展 ,使对流云逐步发展成更大的对流云团 ,从而产生卫星云图中显示的云团发展过程。