A New Approach to Data Assimilation   总被引：1，自引：0，他引：1       下载免费PDF全文

Wang Bin  ZHAO Ying 《Acta Meteorologica Sinica》2006,20(3):275-282

A significant attempt to design a timesaving and efficient four-dimensional variational data assimilation (4DVar) has been made in this paper, and a new approach to data assimilation, which is noted as 'three-dimensional variational data assimilation of mapped observation (3DVM)' is proposed, based on the new concept of mapped observation and the new idea of backward 4DVar. Like the available 4DVar, 3DVM produces an optimal initial condition (IC) that is consistent with the prediction model due to the inclusion of model constraints and best fits the observations in the assimilation window through the model solution trajectory. Different from the 4DVar, the IC derived from 3DVM is located at the end of the assimilation window rather than at the beginning conventionally. This change greatly reduces the computing cost for the new approach, which is almost the same as that of the three-dimensional variational data assimilation (3DVar). Especially, such a change is able to improve assimilation accuracy because it does not need the tangential linear and adjoint approximations to calculate the gradient of cost function. Therefore, in numerical test, the new approach produces better IC than 4DVar does for 72-h simulation of TY9914 (Dan), by assimilating the three-dimensional fields of temperature and wind retrieved from the Advanced Microwave Sounding Unit-A (AMSU-A) observations. Meanwhile, it takes only 1/7 of the computing cost that the 4DVar requires for the same initialization with the same retrieved data.  相似文献   

北极臭氧垂直分布和天气尺度变化的观测研究   总被引：2，自引：0，他引：2  

Zou Han  Zhou Libo  Jian Yongxiao  Liu Yu 《大气科学进展》2002,19(5):855-862

北极地区臭氧对北极气候和环境系统起着重要作用。研究其分布和变化有助于了解北极的气候和环境及其对全球气候系统的影响,有助于气候和环境变化的数值预报。中国北极科学探测1999在北冰洋楚可奇海域成功的进行了大气臭氧观测。通过在中国“雪龙”号破冰船甲板上（于1999年8月18-24日在75°N,160°W附近处）释放大气臭氧探空仪获得了高分辨率的大气垂直结构和臭氧分布资料,可以进行大气尺度的大气臭氧变化研究。分析大气监测资料、TOMS臭氧总量资料和NCEP大气环流资料表明,大气臭氧总量随着对流层顶的低一高一低变化呈高一低一高的变化过程。研究还表明,大气柱的臭氧总量与13公里以下的大气臭氧含量关系密切,而在约20公里处的大气臭氧浓度最大值的变化与整个气柱臭氧的关系不大。500 hPa天气形势图上一个弱一强一弱的西南天气型造成的弱臭氧平流可能是这次臭氧变化的主要原因。  相似文献   

全天空数字相机观测云量的初步研究   总被引：15，自引：1，他引：14  

霍娟  吕达仁 《南京气象学院学报》2002,25(2):242-246

采用带有鱼眼镜头的数字相机拍摄全天空图像,对图像进行处理并分析,实现根据图像获取云量的目的。介绍了工作的基本原理和方法并给出初步实验结果。结果表明,用目前分析图像所获取的算法计算云量（与观测员记录相比）,平均误差在15％以内,结果的准确度受地面能见度影响较大,对能见度达15km以上的图像分析效果最好。  相似文献   

工程控制网测站归心改正的有关问题探讨     

唐诗华 《四川测绘》1998,21(1):26-30

就工程控制网而言,由于其边长较短（一般在2公里左右）,有时为了工作快捷采用多个组同时作业或受地形条件的限制须采用偏心观测,据现行有关文献对测站偏心元素的测定精度要求势必给外业工作带来一定的困难。另外,当边长较短且偏心距较大时,推算控制网各边近似边长的误差相应增大,从而会导致在求取测站归心改正数时出现较大的残余误差,为解决这个问题,本文提出了循环求解归心改正数的方法,并针对实际情况就偏心元素的测定精度要求作了一定的探讨。  相似文献   

Turbulent Statistics of Neutrally Stratified Flow Within and Above a Sparse Forest from Large-Eddy Simulation and Field Observations   总被引：17，自引：13，他引：4  

Hong-Bing Su  Roger H. Shaw  Kyaw Tha Paw  Chin-Hoh Moeng  Peter P. Sullivan 《Boundary-Layer Meteorology》1998,88(3):363-397

Turbulent statistics of neutrally stratified shear-driven flow within and above a sparse forest canopy are presented from a large-eddy simulation (LES) and compared with those from observations within and above a deciduous forest with similar height and foliage density. First- and second-order moments from the LES agree with observations quite well. Third-order moments from the LES have the same sign and similar vertical patterns as those from the observations, but the LES yields smaller magnitudes of such higher-order moments. Turbulent spectra and cospectra from the LES agree well with observations above the forest. However, at the highest frequencies, the LES spectra have steeper slopes than observations. Quadrant and conditional analyses of the LES resolved-scale flow fields also agree with observations. For example, both LES and observation find that sweeps are more important than ejections for the transport of momentum within the forest, while inward and outward interaction contributions are both small, except near the forest floor. The intermittency of the transport of momentum and scalar increases with depth into the forest. Finally, ramp structures in the time series of a passive scalar at multiple levels within and above the forest show similar features to those measured from field towers. Two-dimensional (height-time cross-section) contours of the passive scalar and wind vectors show sweeps and ejections, and the characteristics of the static pressure perturbation near the ground resemble those deduced from field tower-based measurements. In spite of the limited grid resolution (2 m × 2 m × 2 m) and domain size (192 m × 192 m × 60 m) used in this LES, we demonstrate that the LES is capable of resolving the most important characteristics of the turbulent flow within and above a forest canopy.  相似文献   

超声风温仪测温的误差订正   总被引：3，自引：0，他引：3  

张宏升  陈家宜 《大气科学》1998,22(1):11-17

利用同步进行的风速、温度、湿度湍流观测资料,对超声风温仪温度测量结果作了水平风速和湿度的订正。结果表明:由于超声风温仪测温受空气湿度和水平风速的影响,对其作相应的订正是十分必要的。|z/L|＜1时,湿度和风速对超声风温仪温度方差和感热通量测量值所引起的误差是不可忽视的。而在|z/L|＞1区间,仅计入湿度影响,已够精确。对于温度谱密度,当nSθ(n)/σ2θ低于0.01时,有一高频的噪声频率阈值,高于此频率,nSθ(n)/σ2θ与无因次频率f呈+1次幂关系。  相似文献   

对较强地震造成喀什台H磁变仪磁系翻转的处理方法及有关问题的讨论     

郑黎明  高祥真 《内陆地震》1998,12(1):63-67

多年来,Ｈ 磁变仪磁系被地震震翻事件在多震区的地磁台常有发生。这不同程度地影响着磁变仪的正常工作及记录资料的连续性。如何解决这一矛盾,一直是地磁工作者关注的问题。文中主要总结并介绍了喀什台在这方面积累的经验、采取的措施以及收到的效果  相似文献   

水上浅层折射和反射波联合勘探应用研究     

刘保金  王琦 《华北地震科学》1998,16(4):66-70

用浅层折射和反射联合勘探方法在京－沪高速公路沂河桥址区进行隐伏断层和岩性垂直分带控测试验,试验是在宽约４００ｍ的水面上进行的。工作区第四系沉积层和下伏基岩对采用纵波速度作为探测物理量是敏感的,采用ＥＳ－２４０１高分辨率数字地震仪和“五小二高”的工作方法,全方位拾取折射和反射波信息,强化地质推断解释的可靠性,探测试验取得了良好的效果。  相似文献   

聊古—井水氡正常动态的探讨     

潘维双  魏汝庆 《华北地震科学》1998,16(2):60-63

采用相关距平法和增均值法对聊古－井１２年的水氡预测资料进行了处理和分析。从定性、定量两方面描述了聊古－井水氡预测资料的正常年动态呈近直线型。并且从本井水文地球化学背景、阐述了分析、判断水氡测值异常的机理,为本区或邻区地震的预测预报,提供了依据。  相似文献   

辽南地磁场变化与地震   总被引：1，自引：0，他引：1  

辛月提  梁放 《东北地震研究》1998,14(3):17-22

通过对辽南地区流动地磁资料的分析与研究,进一步加深了对辽南地磁场变化的认识。结合１９９７年以来在辽南地区发生的ＭＬ≥４．０地震,根据地震前后地磁场联台差变化,探讨地磁场变化与地震发生的联系。  相似文献