共查询到19条相似文献，搜索用时 481 毫秒
1.
2.
3.
使用共轭码技术，构造了中尺度模式的伴随模式，研究了模式侧边界条件。基于伴随模式技术的原理，设计了伴随同化和Derber同化方法两套方案；下降算法采用共轭梯度法，使用准真实资料，进行子同化数值试验和预报试验。结果表明，两套同化方案都取得了一定的同化效果，Derber同化方法比伴随同化更令人满意。证明了变分同化是提高预报准确率的一种非常有效的手段。 相似文献
4.
CoLM模式地表温度变分同化研究 总被引：2，自引：1，他引：1
本文采用变分方法对通用陆面模式 (CoLM) 中的地表温度进行同化.同化伴随约束条件采用CoLM模式中的地表及植被能量平衡方程,调节因子采用裸土及植被蒸发比.采用美国通量网 (AmeriFlux) 中的Bonville站数据对同化方法进行了单点验证,验证结果表明同化后地表温度以及蒸散结果更加接近于实测值.选取中国华北地区对同化方法进行区域验证,结果显示每天仅采用白天一次观测值对地表温度进行同化的方法是有效的.通过对同化前后地表温度误差直方图比较可以发现,在有MODIS观测值的区域,同化后白天地表温度误差大大降低,同时,同化后地表蒸散空间分布图也发生了变化.单点验证以及区域验证结果都表明了变分同化方法是可靠的.变分同化方法可以改进陆面模式模拟结果,对于地表过程研究中的植被生态、水文等研究具有重要意义,同时,陆面模式可以与数值预报模式进行耦合,改进数值预报结果. 相似文献
5.
多普勒雷达资料4DVAR同化反演的模拟研究 总被引：21，自引：5，他引：21
利用Sun等建立的同化模式和四维变分同化方法对多普勒雷达资料反演大气风场、热力场和微物理场进行了模拟试验研究.反演的基本思路是将4DVAR同化方法应用到三维云模式,定义价值函数表征雷达资料与模式预报结果之间的差别,通过极小化价值函数得到反演场,价值函数相对模式控制变量的梯度由伴随模式求取.试验结果表明,4DVAR同化技术能够从单(双)多普勒雷达资料反演大气三维风场、热力场和微物理场.各个变量反演精度高低与同化过程中变量受约束的大小程度呈正相关.速度场和雨水场反演精度较高,温度场、云水和水汽的反演精度次之,温度场的准确反演需要较长的同化时间.价值函数中加入背景场,哪怕是单点探空给出的平均场信息也有利于提高反演精度.在采用单部多普勒雷达资料进行反演时,速度场的反演误差较大.反演区相对雷达站的位置变化对速度场反演结果有一定的影响,而对其他变量的反演影响很小.两个时次的雷达观测资料基本足够提供反演所需的时间演变信息,同化更多时次的雷达资料,反演效果改进很小.雷达观测资料的缺值会显著降低同化效果,甚至可能导致同化失败,引入背景场可以改善这一状况.4DVAR同化技术对于雷达观测资料误差不太敏感.利用双多普勒雷达合成风场提供水平风场边界条件是比较准确可靠的.在反演主体离边界较远时,VAD风场也基本可用作水平风场边界条件.微物理场的反演对模式中的微物理参数化方案较敏感. 相似文献
6.
4DSVD分析误差与样本选取方法和样本容量的关系初探 总被引：1，自引：0，他引：1
分析误差与样本选取方法和样本容量的关系是4DSVD同化方法一个亟需研究的重要问题。获得支撑大气模式空间和观测空间吸引子的基向量是4DSVD研究的关键部分,样本的好坏和样本容量的范围是决定4DSVD基向量和分析结果质量的一个重要前提条件。首先利用Lorenz28变量模式,用4DSVD方法做了一些简单三维同化试验,探讨了Lorenz28变量模式的分析误差与样本容量和样本选取方法的关系。数值试验结果表明,对一个具体的模式,有限的样本容量就能够获得较高精度的分析结果;在模式系统和观测系统不变情况下,用一定样本容量得到的支撑模式空间和观测空间的基向量具有很好的稳定性,即一旦获得一组较好的基向量,在观测系统和模式系统不变的情况下,对同化任何时刻的观测适用;分析结果对选取方法没有太大的依赖性,但具体的样本容量要视不同模式和样本选取方法而定。用WRF模式做的4DSVD四维观测系统模拟试验结果表明,若样本选取方法得当,所需要的样本容量要远远小于模式自由度。4DSVD要真正获得较高精度的分析结果,需要的条件是尽可能的在吸引子上取样并选取充足的样本容量;间隔取样可以一定程度上减少计算量。根据数值试验结果提出了4DSVD在实际同化时样本选取的一些初步的方法。 相似文献
7.
近来，基于全球定位系统（ＧＰＳ）提出了一种遥感水汽的新途径。根据ＧＰＳ折射率测量结果能够反演出温度和水汽和垂直廓线。对于气象部门来说，这是一种有价值的潜在资料源。基于宾州／ＮＣＡＲ的中尺度模式的绝热版本及其伴随模式发展了一种四维资料同化系统。然后，进行了一系列观测系统模拟试验来评估ＧＰＳ推算的大气折射资料的效果。结果表明，大气折射率同化在反演水汽垂直廓线中是非常有效的。推算出的水汽场的精度明显比用传统反演技术得到的精度要好。大气折射率同化也能提供有效的温度信息。资料同化结果对于附加在模拟折射率观测值上的随机误差较不敏感。而它们对于观测值的空间分辨率却非常敏感。谱分析表明，湿度场具有较小尺度的变化且对大气折射率观测值的分辨率比温度更敏感。当折射率观测值分辨率较粗时，单个观测值同化得到的结果比在模式格点上内插的观测值同化的结果要好。沿大约２４０ｋｍ距离（ＧＰＳ折射率观测的特征尺度）平均的折射率观测值的同化对温度和湿度场的反演仍得到相当好的结果。 相似文献
8.
同化不同观测资料数据集得到的模拟结果大有差异,而实际应用中资料的获取及同化前的预处理也是一项耗时的工作,因此针对不同的研究目的,采用适当的观测资料进行同化是必要的。采用WRF模式同化系统,同化收集到的2种观测资料数据集(分别为全国观测资料数据集和NCEP ADP全球地面观测数据集),并将2种同化试验与未同化模拟结果对比得出:同化不同观测资料数据集对模拟效果影响较大,尤其对垂直方向上的模拟效果影响要大于对地面的;同化国家站数据集在垂直方向上优势明显,但在低空的模拟效果不如加入更多观测数据类型的NCEP ADP数据集的模拟效果;对受局地影响较大的要素,同化对模拟的改善作用显著;相比NCEP ADP数据集,WRF模式在同化国家站数据集后需要更长的积分时间来与之协调,因此选择合适的模式积分开始时间与同化资料的有效时间是必要的。 相似文献
9.
在《中尺度数值模式的资料同化系统——（一）伴随模式的设计》一文的基础上,进一步对伴随模式码的检验问题做了讨论。表明采用共轭码方法是可行的。其导出的伴随模式与理论推导的共轭方程是相容的。试验发现该同化系统有消除随机干扰的能力,同化效果好。在同化过程中,系统是先同化大尺度信息,然后逐步同化中小尺度信息。 相似文献
10.
基于观测数据空间插值、数值模拟以及最优插值同化方法构建了京津冀地区PM2.5(空气动力学当量直径小于等于2.5μm的颗粒物,即细颗粒物)空间插值数据、模拟数据和同化数据,并首次比较分析了三种数据在PM2.5污染回顾分析上的应用潜力和优缺点。针对2014年2月19~28日京津冀地区PM2.5污染过程的分析发现:(1)观测空间插值数据难以完整表征PM2.5污染的时空演变特征,在没有观测覆盖区域误差较大,容易出现虚假的高低值中心;(2)模拟数据具有较高时空分辨率,对PM2.5污染时空演变特征描述更加细致,但在这次污染过程中仍存在较大不确定性,其均方根误差大于100μg/m3;(3)同化数据不仅能对PM2.5空间分布特征进行细致描述,其数据精度在独立验证站点也显著高于模拟数据,其均方根误差比模拟数据低约50%,与站点观测数据的相关系数也比模拟数据高0.2以上。基于PM2.5同化数据,对这次京津冀PM2.5污染过程的时空演变特征进行了详细回顾分析,发现这次污染过程存在自京津冀南部PM2.5污染累积并向北输送发展的生成特点,消亡过程为风向转换下自北向南清除,造成京津冀南部城市先污染后清除,北部城市后污染先清除,并且有慢累积、快清除的特征。从发展演变过程中污染所占空间面积来看,25日PM2.5污染范围最大,覆盖模式第三区域60.5%面积。 相似文献
11.
Summary The design of adaptive observations strategies must account for the particular properties of the data assimilation method. A new adjoint sensitivity approach to the targeted observations problem is proposed in the context of four-dimensional variational data assimilation (4D-Var). The method is based on a periodic update of the adjoint sensitivity field that takes into account the interaction between time distributed adaptive and routine observations. Information provided by all previously located observations is used to identify best locations for new targeted observations. Adaptive observations at distinct instants in time are selected in a sequential manner such that the method is only suboptimal. The selection algorithm proceeds backward in time and requires only one additional adjoint model integration in the assimilation window. Therefore, the method is very efficient and is suitable for practical applications. A comparative performance analysis is presented using the traditional adjoint sensitivity method as well as the total energy singular vectors technique as alternative adaptive strategies. Numerical experiments are performed in the twin experiments framework using a two-dimensional global shallow water model in spherical coordinates and an explicit Turkel-Zwas discretization scheme. Data from a NASA 500mb analysis valid for 00Z 16 Mar 2001 6h obtained with the GEOS-3 model was used to specify the geopotential height at the initial time and the initial velocities were obtained from a geostrophic balance. Numerical results show that the new adaptive observations approach is a promising method for targeted observations and its implementation is feasible for large scale atmospheric models. 相似文献
12.
Keith W. Ayotte 《Boundary-Layer Meteorology》1997,83(2):285-309
This paper describes an adjoint method for data assimilation intoupstream boundary conditions of numerical modelsusing optimal control theory. Mathematical formalisms are given along with the numerical implementation of the schemein a column model of the atmospheric boundary layer. The optimized mean and turbulence profiles are used as an upstream solutionin a model of turbulent flow in complex terrain. To contrast thiswith other methods, two solutions for flow over an isolatedhill are calculated, one with an optimized upstream solution andone with a simple surface-layer formulation for the upstream solution.These two solutions are compared to observations and analytical theory. The adjoint optimization method is shown to producesolutions of flow in complex terrain that are substantively differentat the two solutions, with the optimized solution giving more accurate results. 相似文献
13.
为了建立一个应用于区域数值预报的四维变分资料同化（4DVar）系统,在近期开发的扰动预报模式GRAPES_PF基础上,开发完善增量四维变分同化系统框架。该框架中暂不包含物理过程（长短波辐射、边界层过程、对流参数化和云微物理等）。对比业务使用的GRAPES 3DVar系统,增加了温度控制变量。将无量纲Exner气压与流函数的线性风压平衡方程直接在地形追随垂直坐标面上求解,且通过广义共轭余差法（GCR）求解扰动亥姆霍兹（Helmholtz）伴随方程。利用人造“探空”资料对2015年10月台风“彩虹”进行了理想数值试验。试验结果表明,所开发的扰动四维变分同化框架得到了预期的结果,即同化更多资料并反复受到模式约束的四维变分同化系统能有效改善初值质量,进而改善区域数值预报。建立的区域四维变分同化框架合理可行,为进一步发展包含完整物理过程的区域四维变分同化系统奠定了研究基础。 相似文献
14.
I. Hoteit B. Cornuelle S.Y. Kim G. Forget A. Khl E. Terrill 《Dynamics of Atmospheres and Oceans》2009,48(1-3):175
The problem of dynamically mapping high-frequency (HF) radar radial velocity observations is investigated using a three-dimensional hydrodynamic model of the San Diego coastal region and an adjoint-based assimilation method. The HF radar provides near-real-time radial velocities from three sites covering the region offshore of San Diego Bay. The hydrodynamical model is the Massachusetts Institute of Technology general circulation model (MITgcm) with 1 km horizontal resolution and 40 vertical layers. The domain is centered on Point Loma, extending 117 km offshore and 120 km alongshore. The reference run (before adjustment) is initialized from a single profile of T and S and is forced with wind data from a single shore station and with zero heat and fresh water fluxes. The adjoint of the model is used to adjust initial temperature, salinity, and velocity, hourly temperature, salinity and horizontal velocities at the open boundaries, and hourly surface fluxes of momentum, heat and freshwater so that the model reproduces hourly HF radar radial velocity observations. Results from a small number of experiments suggest that the adjoint method can be successfully used over 10-day windows at coastal model resolution. It produces a dynamically consistent model run that fits HF radar data with errors near the specified uncertainties. In a test of the forecasting capability of the San Diego model after adjustment, the forecast skill was shown to exceed persistence for up to 20 h. 相似文献
15.
Four-dimensional variational data assimilation for mesoscale and storm-scale applications 总被引：1，自引：0，他引：1
Summary ?The status and progress of the four-dimensional variational data assimilation (4DVAR) are briefly reviewed focusing on application
to prediction of mesoscale/storm-scale atmospheric phenomena. Theoretical background is provided for each important component
of the 4DVAR system – forecast and adjoint models, observations, background, cost function, preconditioning, and minimization.
An overview of practical issues specific for mesoscale/storm-scale 4DVAR is then presented in terms of high-resolution observations,
nonlinearity and discontinuity problem, model error, errors from lateral boundary condition, and precipitation assimilation.
Practical strategies for efficient and simplified 4DVAR are also introduced, e.g., incremental 4DVAR, poor man’s 4DVAR, and
inverse 3DVAR. A new concept on hybrid approach is proposed to combine an efficient 4DVAR scheme and the standard 4DVAR scheme
aiming at reducing computational demand required by the standard 4DVAR while improving the accuracy of the simplified 4DVAR.
Applications to both hydrostatic and nonhydrostatic models are illustrated and our vision on opportunities and directions
for future research is provided.
Received March 12, 2001; revised July 24, 2001; accepted September 5, 2001 相似文献
16.
Dynamical and Microphysical Retrieval from Simulated Doppler Radar Observations Using the 4DVAR Assimilation Technique 总被引：3，自引：0，他引：3
Based on a cloud model and the four-dimensional variational (4DVAR) data assimilation method developed by Sun and Crook (1997), simulated experiments of dynamical and microphysical retrieval from Doppler radar data were performed. The 4DVAR data assimilation technique was applied to a cloud scale model with a warm rain parameterization scheme. The 3D wind, thermodynamical, and microphysical fields were determined by minimizing a cost function, defined by the difference between both radar observed radial velocities and reflectivities and their model predictions. The adjoint of the numerical model was used to provide the gradient of the cost function with respect to the control variables. Experiments have demonstrated that the 4DVAR assimilation method is able to retrieve the detailed structure of wind, thermodynamics, and microphysics by using either dual-Doppler or single-Doppler information. The quality of retrieval depends strongly on the magnitude of constraint with respect to the variables. Retrieving the temperature field, cloud water and water vapor is more difficult than the recovery of the wind field and rainwater. Accurate thermodynamic retrieval requires a longer assimilation period. The inclusion of a background term, even mean fields from a single sounding, helped reduce the retrieval errors. Less accurate velocity fields were obtained when single-Doppler data were used. It was found that the retrieved velocity is sensitive to the location of the retrieval domain relative to the radars while the other fields have very little changes. Two radar volumetric scans are generally adequate for providing the evolution, although the use of additional volumes improves the retrieval. As the amount of the observations decreases, the performance of the retrieval is degraded. However, the missing observations can be compensated by adding a background term to the cost function. The technique is robust to random errors in radial velocity and calibration errors in reflectivity. The boundary conditions from the dual-Doppler synthesized winds are sufficient for the retrieval. When the retrieval is mainly controlled by the observations in the regions away from the boundaries, the simple boundary conditions from velocity azimuth display (VAD) analysis are also available. The microphysical retrieval is sensitive to model errors. 相似文献
17.
《Dynamics of Atmospheres and Oceans》2010,49(1-3):175-197
The problem of dynamically mapping high-frequency (HF) radar radial velocity observations is investigated using a three-dimensional hydrodynamic model of the San Diego coastal region and an adjoint-based assimilation method. The HF radar provides near-real-time radial velocities from three sites covering the region offshore of San Diego Bay. The hydrodynamical model is the Massachusetts Institute of Technology general circulation model (MITgcm) with 1 km horizontal resolution and 40 vertical layers. The domain is centered on Point Loma, extending 117 km offshore and 120 km alongshore. The reference run (before adjustment) is initialized from a single profile of T and S and is forced with wind data from a single shore station and with zero heat and fresh water fluxes. The adjoint of the model is used to adjust initial temperature, salinity, and velocity, hourly temperature, salinity and horizontal velocities at the open boundaries, and hourly surface fluxes of momentum, heat and freshwater so that the model reproduces hourly HF radar radial velocity observations. Results from a small number of experiments suggest that the adjoint method can be successfully used over 10-day windows at coastal model resolution. It produces a dynamically consistent model run that fits HF radar data with errors near the specified uncertainties. In a test of the forecasting capability of the San Diego model after adjustment, the forecast skill was shown to exceed persistence for up to 20 h. 相似文献
18.
The importance of specifying realistic lateral boundary conditions in the regional modeling of mineral aerosols has not been examined previously. This study examines the impact of assigning values for mineral aerosol (dust) concentrations at the lateral boundaries of Regional Climate Model version 3 (RegCM3) and its aerosol model over Southwest Asia. Currently, the dust emission module of RegCM3 operates over the interior of the domain, allowing dust to be transported to the boundaries, but neglecting any dust emitted at these points or from outside the domain. To account for possible dust occurring at, or entering from the boundaries, mixing ratios of dust concentrations from a larger domain RegCM3 simulation are specified at the boundaries of a smaller domain over Southwest Asia. The lateral boundary conditions are monthly averaged concentration values (μg of dust per kg of dry air) resolved in the vertical for all four dust bin sizes within RegCM3’s aerosol model. RegCM3 simulations with the aerosol/dust model including lateral boundary conditions for dust are performed for a five year period and compared to model simulations without prescribed dust concentrations at the boundaries. Results indicate that specifying boundary conditions has a significant impact on dust loading across the entire domain over Southwest Asia. More specifically, a nearly 30% increase in aerosol optical depth occurs during the summer months from specifying realistic dust boundary conditions, bringing model results closer to observations such as MISR. In addition, smaller dust particles at the boundaries have a more important impact than large particles in affecting the dust loading within the interior of this domain. Moreover, increases in aerosol optical depth and dust concentrations within the interior domain are not entirely caused by inflow from the boundaries; results indicate that an increase in the gradient of concentration at the boundaries causes an increase of diffusion from the boundaries. Lastly, experiments performed using a climatology of dust concentrations yield similar results to those using actual monthly values. Therefore, using a climatology of dust mixing ratios is sufficient in implementing lateral boundary conditions for mineral aerosols. In short, this work concludes that realistic specification of lateral boundary conditions for mineral aerosols can be important in modeling the dust loading over arid regional climates such as Southwest Asia. 相似文献
19.
Storm track sensitivity to sea surface temperature resolution in a regional atmosphere model 总被引：1，自引：1，他引：0
Tim Woollings Brian Hoskins Mike Blackburn David Hassell Kevin Hodges 《Climate Dynamics》2010,35(2-3):341-353
A high resolution regional atmosphere model is used to investigate the sensitivity of the North Atlantic storm track to the spatial and temporal resolution of the sea surface temperature (SST) data used as a lower boundary condition. The model is run over an unusually large domain covering all of the North Atlantic and Europe, and is shown to produce a very good simulation of the observed storm track structure. The model is forced at the lateral boundaries with 15–20 years of data from the ERA-40 reanalysis, and at the lower boundary by SST data of differing resolution. The impacts of increasing spatial and temporal resolution are assessed separately, and in both cases increasing the resolution leads to subtle, but significant changes in the storm track. In some, but not all cases these changes act to reduce the small storm track biases seen in the model when it is forced with low-resolution SSTs. In addition there are several clear mesoscale responses to increased spatial SST resolution, with surface heat fluxes and convective precipitation increasing by 10–20% along the Gulf Stream SST gradient. 相似文献