Study on the Variational Assimilation Technique for the Retrieval of Wind Fields from Doppler Radar Data

This paper introduces a variational assimilation technique for the retrieval of wind fields from Doppler radar data. The assimilated information included both the radial velocity (RV) and the movement of radar echo. In this assimilation technique, the key is transforming the movement of radar echo to a new radar measuring variable- "apparent velocity" (AV). Thus, the information of wind is added, and the indeterminacy of recovering two-dimensional wind only by AV was overcome effectively by combining RV with AV. By means of CMA GRAPES-3Dvar and CINRAD data, some experiments were performed. The results show that the method of retrieval of wind fields is useful in obtaining the construction of the weather system.     

APPLICATION OF BDA SCHEME IN TYPHOON TRACK PREDICTION

The MM5, which is the PSU/NCAR mesoscale nonhydrostatic limited-area model, and its adjoining modeling system are used in this paper. Taking T106 analysis data as background field the authors generate an optimal initial condition of a typhoon by using two bogus data assimilation schemes, and conduct some numerical simulating experiments. The results of No.9608 typhoon (Gloria) show that the optimal initial field have some dramatic improvements, such as inaccurate position of typhoon center, weaker typhoon circulation and incomplete inner structure of the typhoon, which are caused by shortage of data over the sea. Some improvements have been made in the track forecast. Through several comparing experiments, the initialization optimized by BDA scheme is found to be more reasonable than GFDL scheme and its typhoon track forecast is better.     

多普勒天气雷达资料对中尺度模式短时预报的影响

利用中尺度模式ARPS(The Advanced Regional Prediction System)及其资料分析系统ADAS(ARPS Data Analysis System),将国内新一代多普勒雷达(CINRAD)反射率及径向风资料直接用于中尺度数值模拟,通过一次华北地区暴雨过程的模拟对比试验,分析了雷达资料对初始场的改进效果及其对模拟结果的影响,结果表明:(1)利用雷达径向风资料对初始风场进行调整后,自近地面到对流层顶的u,v,w都发生了变化,调整后的初始风场在对流层中层变化最大.(2)利用雷达反射率进行微物理调整和云分析能调整初始场中的云水信息,使得雷达回波附近3 km以下的水汽混合比(qv)增加,4 km以下的雨水混合比(qr)增加,对流层(约10 km以下)的云水混合比(qc)增加,4～9 km的对流层上部云冰混合比(qi)和雪混合比(qs)增加.ADAS通过非绝热初始化调整温度场,从而得到了一个动力和热力上平衡的初始场.(3)模拟的1 h雨量与实况的对比表明,同时利用雷达反射率和径向风改进过的初始场能明显增强3 h内的降水强度和落区预报,改善中尺度数值模式短时定量降水预报.模拟的1 h流场对比分析表明,经雷达径向风调整后,能够在初始场中增加气旋性涡旋等中小尺度风信息,明显减少模式的spin-up时间.(4)通过对雷达径向风和反射率对模式初始场和模拟结果影响的对比分析发现,雷达径向风主要是改进初始风场,而雷达反射率主要是改进初始场中的湿度参数,增加初始场中云水等的含量,调整温度场.通过模拟的6 h降水对比发现,利用雷达径向风调整初始场后,对降水模拟有一定的改进,但效果不甚明显,而雷达反射率资料对定量降水预报改进效果明显,同时使用雷达径向风和反射率资料改进初始场后对降水的模拟效果最明显.     

嵌套网格空气质量预报模式系统的发展与应用

主要综述中国科学院大气物理研究所自主开发的嵌套网格空气质量预报模式系统(NAQPMS,Nested Air Quality Prediction Modeling System)的历史发展与应用情况.模式发展伊始为欧拉污染物输送实用模型,利用其研究东亚硫氧化物的跨国输送问题,得出中国对于周边国家的输送量不大的结论; 在系统中嵌入适合东亚的起沙机制模块,用来模拟沙尘发生、输送及沉降等过程,估算亚洲大陆沙尘气溶胶对海洋地区的输送与沉降通量,为研究海洋生物地球化学循环提供基础数据; 利用该系统研究沙尘及其土壤粒子对酸雨的中和作用,发现沙尘输送对东亚酸雨的分布影响很大; 发展城市尺度高分辨率气象和空气质量预报技术,使模式水平分辨率达到500 m,并应用于台北高浓度臭氧和PM10的模拟; 研究和集成区域及城市尺度大气污染预报理论和模拟技术,研制成目前的嵌套网格空气质量预报模式系统,以探讨不同尺度各种污染(如沙尘暴、城市光化学烟雾、酸雨、高浓度悬浮颗粒物等)的变化规律.在模式系统中初步建立资料同化模块,开展大气化学成分及沙尘输送模拟的资料同化研究.系统已经在北京、上海、深圳、郑州等城市环境监测中心实施空气质量的实时预报.未来,系统将集成到全球环境大气输送模式(GEATM),以实现从城市群到全球具有双向耦合功能的模式系统.     

Nonlinear Atmospheric and Climate Dynamics in China （2003-2006）： A Review

Recent advances in the study of nonlinear atmospheric and climate dynamics in China （2003 2006） are briefly reviewed. Major achievements in the following eight areas are covered： nonlinear error dynamics and predictability; nonlinear analysis of observational data; eddy-forced envelope Rossby soliton theory; sensitivity and stability of the ocean＇s thermohaline circulation; nonlinear wave dynamics; nonlinear analysis on fluctuations in the atmospheric boundary layer; the basic structures of atmospheric motions; some applications of variational methods.     

UKF滤波算法在数据同化中的应用

介绍了一种新的数据同化算法（UKF，Unscented Kalman Filter），该算法不需要计算伴随矩阵，就能够解决模式的非线性问题。以Lorenz系统为例，进行了数据同化的数值试验。结果表明：基于UKF的同化方案与背景场的初始值无关，它能有效地抑制状态变量误差的增长，同化结果精度高。     

THE EFFECTS OF BOGUS TYPHOON AND OBSERVED OCEANIC DATA ON THE ABILITY OF T_(213)L_(31) TO PREDICT TC TRACK

The abilities of typhoon (TC) track prediction by a medium-range forecast model T213L31 at National Meteorological Center are analyzed and its ability to improve its TC forecasts is discussed. The results show that about 57% of the TCs could be predicted by T213L31 but the initial position errors are large.The 43% area without the prediction of TC tracks is concentrated between 13°N and 20°N and east of 120°E and lack of conventional observation data is the main reason for the absence of TC prediction in this area.The adding of bogus TC could improve the ability of TC track prediction when there is no TC vortex in the analysis field, but could only have positive effects on the short-range TC track prediction when there is TC vortex in the T213L31 analysis field.     

A review on reflective remote sensing and data assimilation techniques for enhanced agroecosystem modeling

During the last 50 years, the management of agroecosystems has been undergoing major changes to meet the growing demand for food, timber, fibre and fuel. As a result of this intensified use, the ecological status of many agroecosystems has been severely deteriorated. Modeling the behavior of agroecosystems is, therefore, of great help since it allows the definition of management strategies that maximize (crop) production while minimizing the environmental impacts. Remote sensing can support such modeling by offering information on the spatial and temporal variation of important canopy state variables which would be very difficult to obtain otherwise.In this paper, we present an overview of different methods that can be used to derive biophysical and biochemical canopy state variables from optical remote sensing data in the VNIR-SWIR regions. The overview is based on an extensive literature review where both statistical–empirical and physically based methods are discussed. Subsequently, the prevailing techniques of assimilating remote sensing data into agroecosystem models are outlined. The increasing complexity of data assimilation methods and of models describing agroecosystem functioning has significantly increased computational demands. For this reason, we include a short section on the potential of parallel processing to deal with the complex and computationally intensive algorithms described in the preceding sections.The studied literature reveals that many valuable techniques have been developed both for the retrieval of canopy state variables from reflective remote sensing data as for assimilating the retrieved variables in agroecosystem models. However, for agroecosystem modeling and remote sensing data assimilation to be commonly employed on a global operational basis, emphasis will have to be put on bridging the mismatch between data availability and accuracy on one hand, and model and user requirements on the other. This could be achieved by integrating imagery with different spatial, temporal, spectral, and angular resolutions, and the fusion of optical data with data of different origin, such as LIDAR and radar/microwave.     

复杂地形下地面观测资料同化II. 模式地形与观测站地形高度差异代表性误差

第I部分研究结果(徐枝芳等,2007)表明模式与实际观测站地形高度差异对地面观测资料同化效果有较大影响。此文在MM5_3DVAR同化系统中利用近地层相似理论将地面观测资料进行直接三维变分同化分析,考虑模式与实际观测站地形高度差异对同化效果的影响,提出在地面观测误差中增加地形代表性误差来解决这个问题。研究结果表明:地面资料同化分析时,在其观测误差中加入一项新的误差——地形代表性误差,能较好地解决地面资料同化分析中模式与观测站地形高度差异问题;地面资料参与同化分析,在观测误差中加入与模式和实际观测站地形高度差异大小相关的地形代表性误差时,地面观测值对分析值的影响随着地形高度差异代表性误差的加入而减小,同时又部分地将地面观测信息通过变分分析融进分析场,使得低层分析更接近真实场,且地面资料利用率更高,24小时降水数值预报(模拟)的效果较好。