边界层中风速向Ekman气流的调整

在自由大气中,风压场之间基本上是满足地转平衡的,但在某些局部地区,可以出现地转偏差,而这些偏差通过惯性重力外波的频散作用将最终消灭而建立起地转平衡。这种适应过程已有很多的研究。与自由大气中的准地转气流的特征相似,在边界层中,在三种力即折向力、气压梯度力和湍流粘性力的平衡下,风场呈现Ekman气流,即风速矢量湍迹呈现Ekman螺线。类似于地转适应问题的提法,在边界层中,也存有Ekman气流的适应问题。即当初始场在某种原因下,风场、压力场之间与Ekman气流     

正压原始方程变分初值试验

本文利用地转风关系及运动方程作为动力约束条件,对初始风场及高度场进行了调整。在调整场与实测场均方差最小,总平均动能损失也最小的条件下选择了权重因子。还成功地进行了局部风场“嵌入”即所谓“窗户”区试验。对于变分约束对扰动的影响作了初步的探讨。最后还做了24小时预报并与地转初值预报进行了比较。     

Rossby波传播的物理机制

本文指出地转平衡条件下经向风场的交替反向变化使单纯正压Rossby波向西传播,西风场的这种交替变化,是由随着科氏参数的纬向变化而产生的微小经向气压梯度引起的.     

在变分法中利用地面气压变差分析“SIGMA”面上的水平和垂直流场

1. 前言 对于数值初值化问题,目前最满意的方法是经Machen bauer(1977)、Temperton和Williomson(1979)改进的标准型初值化方法。Kitade(1982)提出了非绝热非线性标准型初值化方案并检验了初值化在预报热带扰动问题上的影响,这个方法也许是最简单的方法之一。但是如果考虑连续方程的约束并结合地面气压倾向值来分析初始风场,就不需要非线性标准型初值化。 另外,在青藏高原、落矶山山脉等大尺     

几种Q矢量的比较

利用 1 991 - 0 7- 0 5T2 0— 0 6T2 0一次江淮梅雨锋暴雨过程实况资料 ,结合地面降水分布 ,从定性 (矢量场 ,即 Q)、定量 (散度场 ,即 2 · Q)的角度细致、具体地比较分析了准地转 Q矢量、半地转 Q矢量、非地转 Q矢量及湿 Q矢量的诊断特性。结果表明 :半地转 Q矢量诊断能力优越于准地转 Q矢量。非地转 Q矢量、湿 Q矢量诊断能力明显优越于准地转 Q矢量、半地转 Q矢量。准地转 Q矢量诊断能力最差 ;从定性的角度分析 ,非地转 Q矢量与湿 Q矢量诊断能力相差不大。但进一步定量分析发现 ,在整个梅雨锋暴雨过程中 ,湿 Q矢量的诊断能力大于其他 Q矢量 ;70 0 h Pa高度上各 Q矢量的矢量、散度辐合区较其在 850 h Pa和 50 0 h Pa上对降水反映更好 ,尤其是70 0 h Pa湿 Q矢量散度辐合区与降水区有非常好的对应关系。     

南半球环状模事件的准地转调整过程分析

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.     

应用测风资料形成原始方程初值的一个方法

本文给出一个应用实测风和位势场形成原始方程模式初值的方法,取质量散度垂直积分为零作为约束条件。调整实测风,消去初始风场中的重力外波。计算结果是稳定的,预报的场是光滑的。这个方法尤其适用于形成产生暴雨的次天气尺度系统的初值。     

几种Q矢量的比较

利用1991-07-05T20—06T20一次江淮梅雨锋暴雨过程实况资料,结合地面降水分布,从定性(矢量场,即Q)、定量(散度场,即2∇·Q)的角度细致、具体地比较分析了准地转Q矢量、半地转Q矢量、非地转Q矢量及湿Q矢量的诊断特性。结果表明:半地转Q矢量诊断能力优越于准地转Q矢量。非地转Q矢量、湿Q矢量诊断能力明显优越于准地转Q矢量、半地转Q矢量。准地转Q矢量诊断能力最差;从定性的角度分析,非地转Q矢量与湿Q矢量诊断能力相差不大。但进一步定量分析发现,在整个梅雨锋暴雨过程中,湿Q矢量的诊断能力大于其他Q矢量;700hPa高度上各Q矢量的矢量、散度辐合区较其在850hPa和500hPa上对降水反映更好,尤其是700hPa湿Q矢量散度辐合区与降水区有非常好的对应关系。     

暴雨系统中的非平衡运动与有限区域模式的初值化

将非平衡风分成两部分:(1)非平街风的旋度部分(?)′_R和(2)非平衡风的散度部分(?)′_D。在产生暴雨的次天气尺度系统中,这两种非平衡风具有同样重要的作用。所以在有限区域细网格模式的初值化中,不能只考虑散度风,即使用通常称为“散度初值化”的方案,而且要考虑非平衡风的旋度部分。根据散度方程分析,(?)′_R是维持、调整散度场的重要因子。试验了三种风场初值化方案,结果表明,在风场初值中同时考虑(?)′_R和(?)′_D,可以明显改善模式的降水预报。     

正压原始方程模式采用准拉格朗日格式的预报试验

本文设计了一个时间积分采用准拉格朗日格式的台风路径预报的正压原始方程模式。模式采用海绵型开放边界,使边界附近的预报有所改进。采用海绵型边条件和准拉格朗日平流格式后,模式的计算稳定性较好。积分24小时,区域总能量和涡度拟能变化小于1%。在用实际观测资料所做的台风路径预报试验中,初始风场的散度是作为源项加到连续方程中的。对比试验结果表明:有实际源项的初始场的预报优于无源项和源项被人为改变了的初始场的预报,从而说明起始风场中包括非地转部分有利于改善台风路径预报。     

Remote Sensing Of Three-Dimensional Winds With Elastic Lidar: Explanation Of Maximum Cross-Correlation Method

Maximum cross-correlation provides a method to remotely determine highly resolved three-dimensional fields of horizontal winds with elastic lidar throughout large volumes of the planetary boundary layer (PBL). This paper details the technique and shows comparisons between elastic lidar winds, remotely sensed laser Doppler velocimeter (LDV) wind profiles, and radiosonde winds. Radiosonde wind data were acquired at Barcelona, Spain, during the Barcelona Air-Quality Initiative (1992), and the LDV wind data were acquired at Sunland Park, New Mexico (N.M.), during the Border Area Air-Quality Study (1994). Comparisons show good agreement between the different instruments, and demonstrate the method useful for air pollution management at the local/regional scale. Elastic lidar winds could thus offer insight into aerosol and pollution transport within the PBL. Lidar wind fields might also be used to nudge or improve initialization and evaluation of atmospheric meteorological models.     

Assimilating QuikSCAT Ocean Surface Winds with the Weather Research and Forecasting Model for Surface Wind-Field Simulation over the Chukchi/Beaufort Seas

To achieve a high-quality simulation of the surface wind field in the Chukchi/Beaufort Sea region, quick scatterometer (QuikSCAT) ocean surface winds were assimilated into the mesoscale Weather Research and Forecasting model by using its three-dimensional variational data assimilation system. The SeaWinds instrument on board the polar-orbiting QuikSCAT satellite is a specialized radar that measures ice-free ocean surface wind speed and direction at a horizontal resolution of 12.5 km. A total of eight assimilation case studies over two five-day periods, 1–5 October 2002 and 20–24 September 2004, were performed. The simulation results with and without the assimilation of QuikSCAT winds were then compared with QuikSCAT data available during the subsequent free-forecast period, coastal station observations, and North American Regional Reanalysis data. It was found that QuikSCAT winds are a potentially valuable resource for improving the simulation of ocean near-surface winds in the Chukchi/Beaufort Seas region. Specifically, the assimilation of QuikSCAT winds improved, (1) offshore surface winds as compared to unassimilated QuikSCAT winds, (2) sea-level pressure, planetary boundary-layer height, as well as surface heat fluxes, and (3) low-level wind fields and geopotential height. Verification against QuikSCAT data also demonstrated the temporal consistency and good quality of QuikSCAT observations.     

FY-2C云迹风资料同化应用对台风预报的影响试验研究

针对0505号台风“海棠”, 采用WRF区域中尺度模式进行控制试验和两个同化试验, 利用WRF-3DVAR同化系统同化FY-2C红外和水汽两个通道云迹风反演产品, 同化分云迹风经质量控制和未经质量控制两组同化试验。通过三组试验分析云迹风资料对降水和风场等的预报结果的影响, 并进行24小时降水量分级Ts评分检验以及风场点对点检验。结果表明: 同化经质量控制云迹风资料可以提高降水落区和强度预报的准确度, 不同等级的Ts评分较其它试验都有较明显改进; 风场预报模拟也有所改善。增加两例台风, 使用与“海棠” 相似的处理方法进行模拟试验, 并对模拟结果24小时降水分析与检验, 得到与“海棠”类似结论。因此, 经过合理性选择的云迹风资料的加入, 有利于补充初始场中可能未包含的中尺度信息, 从而提高试验中对于降水、风场等的模拟效果, 提高WRF模式的模拟预报能力。     

Observational Study of Surface Wind along a Sloping Surface over Mountainous Terrain during Winter

The 2018 Winter Olympic and Paralympic Games will be held in Pyeongchang, Korea, during February and March. We examined the near surface winds and wind gusts along the sloping surface at two outdoor venues in Pyeongchang during February and March using surface wind data. The outdoor venues are located in a complex, mountainous terrain, and hence the near-surface winds form intricate patterns due to the interplay between large-scale and locally forced winds. During February and March, the dominant wind at the ridge level is westerly; however, a significant wind direction change is observed along the sloping surface at the venues. The winds on the sloping surface are also influenced by thermal forcing,showing increased upslope flow during daytime. When neutral air flows over the hill, the windward and leeward flows show a significantly different behavior. A higher correlation of the wind speed between upper-and lower-level stations is shown in the windward region compared with the leeward region. The strong synoptic wind, small width of the ridge, and steep leeward ridge slope angle provide favorable conditions for flow separation at the leeward foot of the ridge. The gust factor increases with decreasing surface elevation and is larger during daytime than nighttime. A significantly large gust factor is also observed in the leeward region.     

Remote Sensing of Three-dimensional Winds with Elastic Lidar: Explanation of Maximum Cross-correlation Method

Maximum cross-correlation provides a method toremotely de-ter-mine high-lyre-solved three-dimensional fields of horizontalwinds with e-las-tic li-darthrough-out large volumes of the planetaryboundary layer (PBL). This paperdetails the technique and shows comparisonsbetween elastic lidar winds, remotelysensed laser Doppler velocimeter (LDV) windprofiles, and radiosonde winds.Radiosonde wind data were acquired at Barcelona,Spain, during the BarcelonaAir-Quality Initiative (1992), and the LDVwind data were acquired at SunlandPark, New Mexico during the 1994 Border AreaAir-Quality Study. Comparisonsshow good agreement between the differentinstruments, and demonstrate the methoduseful for air pollution management at thelocal/regional scale. Elastic lidar windscould thus offer insight into aerosol andpollution transport within the PBL. Lidarwind fields might also be used to nudge orimprove initialization and evaluation ofatmospheric meteorological models.     

The impact of the assimilation of scatterometer winds on surface wind and wave forecasts

Recent work has demonstrated that surface marine winds from the Bureau of Meteorology's operational Numerical Weather Prediction (NWP) systems are typically underestimated by 5 to 10%. This is likely to cause significant bias in modelled wave fields that are forced by these winds. A simple statistical adjustment of the wind components is shown to reduce the observed bias in Significant Wave Height considerably. The impact of increasing the vertical resolution of the NWP model and assimilating scatterometer data into the model is assessed by comparing the resulting forecast wind and waves to observations. It is found that, in general, the inclusion of scatterometer observations improves the accuracy of the surface wind forecasts. However, most of the improvement is shown to arise from the increased number of vertical levels in the atmospheric model, rather than directly from the use of the observations. When the wave model is forced with surface winds from the NWP model that includes scatterometer data, it is found that the scatterometer assimilation does not reduce the systematic bias in surface wave forecasts, but that the random errors are reduced.     

An improved method for doppler wind and thermodynamic retrievals

A variational method is developed to retrieve winds in the first step and then thermodynamic fields in the second step from Doppler radar observations. In the first step, wind fields are retrieved at two time levels: the beginning and ending times of the data assimilation period, simultaneously from two successive volume scans by using the weak form constraints provided by the mass continuity and vorticity equations.As the retrieved wind fields are expressed by Legendre polynomial expansions at the beginning and ending times, the time tendency term in the vorticity equation can be conveniently formulated, and the retrieved winds can be compared with the radar observed radial winds in the cost function at the precise time and position of each radar beam. In the second step, the perturbation pressure and temperature fields at the middle time are then derived from the retrieved wind fields and the velocity time tendency by using the weak form constraints provided by the three momentum equations. The merits of the new method are demonstrated by numerical experiments with simulated radar observations and compared with the traditional least squares methods which consider neither the precise observation times and positions nor the velocity time tendency. The new method is also applied to real radar data for a heavy rainfall event during the 2001 Meiyu season in China.     

双雷达风场反演拼图在登陆台风“莫兰蒂”(1614)强降水精细预报中的同化应用试验

利用福建龙岩、漳州、泉州新一代多普勒天气雷达和厦门海沧双偏振雷达探测资料,采用动态地球坐标系下双雷达三维风场反演与拼图技术,基于天气研究和预报模式（Weather Research and Forecasting,WRF）及其资料同化系统,对登陆台风“莫兰蒂”（1614）引起的2016年9月14—15日福建强降水过程进行了双雷达风场反演拼图资料检验及其三维变分同化对强降水精细预报影响的数值试验,结果发现:（1）动态地球坐标系下双雷达反演风场能合理反映实际风场分布状况,其误差相对较小。相较厦门翔安风廓线雷达及厦门探空秒级测风数据,反演风风向（风速）平均绝对误差分别为7.8°（2.6 m/s）及3.4°（1.1 m/s）;（2）反演风场水平方向稀疏化对同化及预报结果极为重要,过密的反演风场资料会给同化及预报结果带来负效果。文中采用18、6、2 km 3重嵌套,在3重嵌套区域均进行同化以及仅在2 km区域进行同化两种情况下,均表现为当反演风场资料水平分辨率提高到0.1°时,同化分析及预报的台风环流开始受到负影响;且当反演风场资料水平分辨率越高时,负效果越明显。敏感性试验结果显示,分辨率取0.2°时数值预报效果最好;（3）以美国国家环境预报中心全球预报系统（National Centers for Environmental Prediction/Global Forecast System,NCEP/GFS）0.5°×0.5°分析场为初值,基于3个不同起报时刻（2016年9月14日14时、20时及15日02时）（北京时,下同）模拟的福建省境内台风内核雨带和螺旋雨带逐时演变、台风路径与强度、逐时降水TS评分和空间相关差异显著,其中14日14时起报试验效果最好;而14日20时起报试验效果最差,这与该试验初始台风大风轴风速明显偏大有关;（4）在上述3个不同起报时刻试验基础上,分别增加双雷达反演风场资料的三维变分同化后,福建境内地面风场和台风内核雨带、螺旋雨带逐时分布、逐时降水TS评分和空间相关、台风环流结构以及U、V风垂直廓线分布均有明显改善,最大正影响时效可达24 h;但仅对1—6 h时效内台风路径有改善。      

Wind energy estimates by use of a diagnostic model

A diagnostic model is a relatively simple and practical tool for modeling the wind flow of the boundary layer in complex terrain. The model begins with a wind analysis based on available surface wind reports and geostrophic winds (computed from pressure data). The height of the boundary layer top (upper surface of the computational domain) is prescribed to fit local conditions. Using the continuity equation in terrain-following coordinates, the winds at mesh points are adjusted to produce nondivergence while maintaining the original vertical component of vorticity. The method of computing the nondivergent winds uses direct alterations. This method may be useful for other modeling purposes and will be described. Data for a long period (usually a year) are analyzed to obtain eigenvectors and the associated time series of their coefficients at each observation time. The model is run only for the five or six eigenvectors that explain most of the variance. The wind field at any particular time is reconstructed from the eigenvector solutions and their appropriate coefficients. Comparisons of model results with measured winds at sites representing different types of terrain will be shown. The accuracy and economy of the model make it a useful tool for estimating wind energy and also for giving wind fields for low-level diffusion models.     

The use of successive dynamic initialization by nudging to simulate cyclogenesis during GALE IOP 1

Summary Synoptic/diagnostic case studies have increasingly come to rely on numerical simulations started from some initial state after which the model generated fields receive no further information from observed data. The purpose of this paper is to demonstrate the use of a dynamic data assimilation technique based on nudging to create a dynamically consistent high-resolution four-dimensional data set that can be used for synoptic diagnostic studies. The nudging technique is applied in the Goddard Mesoscale Atmospheric Simulation System (GMASS) using the 3-h radiosonde data collected during GALE IOP 1. A unique aspect of this application is nudging toward data analyses for which the areal coverage shifts with time. One of the two nudging simulations assimilates surface pressure in addition to the temperature, mixing ratio, and wind components. The nudging values are determined by linear interpolation between 3-h observation times. Assuming a linear variation of the assimilated value in time leads to estimates of the nudging coefficients which take into account the accuracy of the observations.Both nudging simulations are more accurate in terms of S hand root-mean-square error (RMSE) scores than a control sunulation without successive initialization. The nudging simulation with surface pressure is more accurate than the nudging simulation without surface pressure assimilation for this case. The simulation with surface pressure nudging captures the surface cyclogenesis and the associated strong rise-fall couplet in the 500 hPa height field. It also exhibits the strongest ageostrophic flow and exit region vertical circulation associated with a jet streak on the western side of the intensifying upper-level trough.The data sets made possible by the dynamic assimilation/ simulation cycles are dynamically consistent, have high spatial and temporal resolution and are ideally suited for diagnostic studies. Examples presented include the evolution of the ageostrophic flow associated with the exit region of an upper-level jet propagating toward the base of an intensifying trough with increasing cyclonic curvature of the flow. The nudging simulation with surface pressure provides the resolution and accuracy required to depict the rapid transformation (within a 12-h period) of the exit region ageostrophic flow from predominantly cross contour to along contour as the jet streak approaches the base of the trough.With 19 Figures