A technique for modeling the Earth’s gravity field on the basis of satellite accelerations   总被引：3，自引：2，他引：1  

P. Ditmar  A. A. van Eck van der Sluijs 《Journal of Geodesy》2004,78(1-2):12-33

A technique is proposed for Earths gravity field modeling on the basis of satellite accelerations that are derived from precise orbit data. The functional model rests on Newtons second law. The computational procedure is based on the pre-conditioned conjugate-gradient (PCCG) method. The data are treated as weighted average accelerations rather than as point-wise ones. As a result, a simple three-point numerical differentiation scheme can be used to derive them. Noise in the orbit-derived accelerations is strongly dependent on frequency. Therefore, the key element of the proposed technique is frequency-dependent data weighting. Fast convergence of the PCCG procedure is ensured by a block-diagonal pre-conditioner (approximation of the normal matrix), which is derived under the so-called Colombo assumptions. Both uninterrupted data sets and data with gaps can be handled. The developed technique is compared with other approaches: (1) the energy balance approach (based on the energy conservation law) and (2) the traditional approach (based on the integration of variational equations). Theoretical considerations, supported by a numerical study, show that the proposed technique is more accurate than the energy balance approach and leads to approximately the same results as the traditional one. The former finding is explained by the fact that the energy balance approach is only sensitive to the along-track force component. Information about the cross-track and the radial component of the gravitational potential gradient is lost because the corresponding force components do no work and do not contribute to the energy balance. Furthermore, it is shown that the proposed technique is much (possibly, orders of magnitude) faster than the traditional one because it does not require the computation of the normal matrix. Hints are given on how the proposed technique can be adapted to the explicit assembling of the normal matrix if the latter is needed for the computation of the model covariance matrix.Acknowledgments. Professor R. Klees is thanked for support of the project and for numerous fruitful discussions. The authors are also thankful to Dr. J. Kusche for useful remarks and to Dr. E. Schrama, his solid background in satellite geodesy proved to be very helpful. A large number of valuable comments were made by Dr. S.-C. Han, Dr. P. Schwintzer, and an anonymous reviewer; their contribution is greatly acknowledged. The satellite orbits used in the numerical study were kindly provided by Dr. P. Visser (Aerospace Department, Delft University of Technology). Access to the SGI Origin 3800 computer was provided by Stichting Nationale Computerfaciliteiten (NCF), grant SG-027.  相似文献   

Effects of the number of stations and time resolution on derivation     

Odim Mendes  Jr.  Aracy Mendes da Costa  Fernando Celso Perin Bertoni 《Journal of Atmospheric and Solar》2006,68(18):2127-2137

For at least 30 years now it has been well known that the Dst index can be modelled using the solar wind as input. Since then, many attempts have been made to improve the predictability of Dst using different approaches. These attempts are useful, for instance, to understand which features of the solar wind–magnetosphere interactions are most important in producing magnetospheric activity and how the Dst index would improve the space weather forecast. The Dst index is by far the most reliable and simple indication that a magnetic storm is in progress. In this work, the effect of using more than four magnetic stations and shorter time intervals than the hourly averages used in Sugiura's procedures is evaluated. The discussion is based on the results presented by Burton in 1975 and Feldstein in 1984 considering 4 or 12 magnetic stations and time averages of 2.5 min for a magnetic disturbed period that occurred from February 7–28, 1967, including two geomagnetic storms. The analysis has shown that the global representation of a magnetic storm by the standard Dst (Sugiura) is well preserved either using 4, 6, 12 magnetic stations or using 1 h, 2.5 min 1 min averages. A brief review of the current understanding of Dst has been included to support the discussions. The analysis performed has shown that a more refined Dst index (time and number of stations>4) would be useful to investigate the intrinsic processes and the different current systems involved in the ring current development during magnetic storms; the standard Dst, as it is conceived, is quite adequate to monitor geomagnetic storms and identify their overall features; concerning the magnetic stations normally considered, the inclusion of higher magnetic latitude stations (>35) may underestimate the observed Dst.  相似文献   

Unstable kinetic Alfvén wave in partially ionized plasma     

J. Vranjes  D. Petrovic  M. Kono 《Planetary and Space Science》2006,54(6):641-644

The stability of kinetic Alfven waves is discussed for a partially ionized plasma with a flux of ionizing electrons which balance the plasma particle losses. Accidental electromagnetic perturbations are shown to be unstable due to the energy change of ionizing electrons.  相似文献   

全国矿产资源规划信息数据库及管理系统的构建   总被引：1，自引：0，他引：1  

刘臻  任效颖 《国土资源信息化》2012,(2):39-44

随着矿产规划管理信息的逐渐增多和矿政管理部门的需求不断提高,本文根据规划管理的业务需求以及第二轮的矿产资源规划标准,建立了全国矿产资源规划信息数据库管理系统。通过Oracle 10g建立矿产资源规划信息数据库,并通过ArcGIS Engine构建管理系统,实现了全国矿产资源规划信息的整合与共享,为矿产规划管理的科学化、精细化提供了依据。  相似文献   

26Al/10Be等时线埋藏测年法基本原理与应用简介          下载免费PDF全文

孙政  沈冠军  赖忠平 《盐湖研究》2012,20(2):66-72

介绍了26Al/10Be等时线埋藏测年法的基本原理及其主要应用范围。将应被同时埋藏的一组石英矿物样的26Al-10Be浓度拟合成等时线,从其斜率解得样品的埋藏年代。在如下情况下该法可克服未知参数多于制约方程的困难:1)冰碛物-古土壤序列中古土壤形成年代的研究,以规避继承核素(inherited nu-clide)的干扰;2)因样品埋藏不够深引起的后期生成核素的干扰。此外,依据等时线拟合结果可判断样品是否符合简单恒态侵蚀模式。等时线法的引入,拓宽了埋藏测年的应用范围,并为埋藏测年数据可信度提供了一种有效的验证手段。  相似文献   

中国北方典型沙尘天气特征研究   总被引：4，自引：1，他引：3  

吕艳丽  刘连友  屈志强  胡霞 《中国沙漠》2012,32(2):447-453

 根据API、风速、风向及相关气象数据初步研究了中国北方两次典型沙尘天气的天气特征。两次沙尘天气过程中极大风速大于7.2 m·s-1的气象站占88%。2005年4月27日极大风速超过17.2 m·s-1的气象站有31个,出现频率最高的风向为西西北,28日达到81个,风向为北风,极大风速高值区由内蒙古中东部向东北方向迅速扩大。2007年3月30日极大风速超过17.2 m·s-1的气象站有57个,31日达到68个,风向均为西西北,极大风速高值区分布较为稳定。受沙尘暴影响的地区API显著升高。2005年4月28日呼和浩特、大同、北京3个城市的API分别为418、500、500。2007年3月31日呼和浩特、赤峰、大同3个城市的API分别为500、500、423。对PM10与气象因子的相关性进行分析得出,沙尘暴期间,大气中可吸入颗粒物的浓度与风速存在显著的正相关关系,风速越高的地区,可吸入颗粒物的浓度越大。  相似文献   

Model-Experimental Analysis of Variational Assimilation of Dust Concentration with GRAPES Sand-Dust Numerical Forecasting System in a Sand-Dust Storm     

《高原气象》2012,31(3)

为了提高沙尘模式的预报准确率,通过在区域天气数值模式GRAPEs（G10bal／RegionalAs-similationandPrEdictionSystem）的三维变分同化系统中增加沙尘浓度这一控制变量的方法建立了GRAPES-3DVAR-DusT沙尘同化系统。利用中国北方8个观测站提供的沙尘PM10数据和沙尘模式（GRAPEs-CUAcE／Dust系统）提供的背景场,对2008年2月29日-3月1日发生在中国北方的一次沙尘暴天气进行了控制试验和一次同化与间断同化的敏感性试验,结果表明：（1）引入该同化系统后,一次同化和间断同化试验模拟的地面沙尘浓度分布较未同化的控制试验结果更接近卫星监测,而间断同化的结果又好于一次同化;（2）一次同化试验与控制试验对单站PM10浓度的演变预报较差;（3）间断同化试验较准确地再现了单站PM10浓度的连续演变;（4）间断同化试验效果整体上优于一次同化试验。总体而言,引入沙尘同化系统在一定程度上可以提高沙尘模式对沙尘天气的预报准确率。  相似文献   

大同地区典型沙尘天气过程近地层气象要素演变特征的对比分析     

郝玉峰  施占军  王淑凤 《山西气象》2012,(1):25-28

利用2009年3月-2010年3月大同国家基准气候站20m气象梯度塔的风向、风速、气温、相对湿度的观测资料及PM10质量浓度数据、气溶胶散射系数数据,分析大同地区典型沙尘天气过程近地层气象要素演变特征。结果表明,风速在沙尘暴、扬沙的发生、发展过程中均较大,浮尘较小。气温在沙尘暴期间受冷空气的影响迅速减小,而在扬沙和浮尘天气条件下温度的变化主要取决于长短波辐射的强弱和沙尘气溶胶的辐射强迫。相对湿度在沙尘暴期间基本上呈递增态势,结束后比发生前相对湿度增大,在扬沙和浮尘天气条件下,相对湿度与温度完全呈现出反相关关系,且相对湿度均较小。PM10质量浓度在沙尘暴、扬沙、浮尘天气条件下依次递减。沙尘暴期间气溶胶散射系数明显增大。  相似文献   

2010年沙尘天气对巴彦浩特空气质量的影响   总被引：1，自引：0，他引：1  

常佩静  张斯莲  王多民  潘明 《内蒙古气象》2012,(3):18-20

利用巴彦浩特2010年1月至2011年2月PM10、SO2、NO2的逐日监测数据和同一时期气象观测资料,分析巴彦浩特空气污染物特征及PM10浓度与沙尘天气之间的关系。分析结果表明:2010年春、夏、秋三季巴彦浩特的主要污染物是PM10,冬季主要污染物是SO2;沙尘天气是造成巴彦浩特PM10浓度变化的最重要因素;影响巴彦浩特空气质量的沙尘主要来源于其西北方向和西北偏北方向。建议有关部门在巴彦浩特西北地区搞好生态保护与建设,以减轻沙尘天气对巴彦浩特地区空气质量的影响。  相似文献   

南京市城市不同功能区PM₁₀和PM_2.1质量浓度的季节变化特征     

王红磊  朱彬  康汉青  沈利娟  潘晨 《气象科学》2012,32(S1):16-23

使用Anderson-Ⅱ型9级撞击采样器测量了南京市鼓楼商业区、江北工业区、钟山风景区和宁六高速公路交通源春、夏、秋三季的大气气溶胶质量浓度。分析结果表明:南京市PM_2.1和PM₁₀的质量浓度存在明显的季节变化,秋季>春季>夏季;ρ_PM10春季为167.47 μg/m³,夏季为 85.99 μg/m³,秋季为238.99 μg/m³;ρ_PM2.1春季为59.66 μg/m³,夏季为42.80 μg/m³,秋季为100.15 μg/m³。不同季节中ρ_PM10和ρ_PM2.1均存在较好的相关性,夏季相关性最好,相关系数为0.952;秋季次之,相关系数为0.783;春季相对较差,相关系数为0.613。城市不同功能区之间ρ_PM2.1和ρ_PM10的质量浓度值差异很大,交通源>工业区>商业区>风景区。城市不同功能区的质量浓度谱分布基本一致,均为双峰型分布,峰值分别位于0.43~0.65 μm/m³和9.0~10.0 μm/m³。南京市春、夏、秋三个季节大气粒子质量浓度谱为双峰分布,粒子主要集中在0.43~3.3 μm/m³的粒径段。江北工业区ρ_PM10和ρ_PM2.1质量浓度的相关系数为0.814,略高于鼓楼商业区的0.797。  相似文献