计算稳定性的若干问题   总被引：15，自引：4，他引：15  

曾庆存 《大气科学》1978,2(3):181-191

偏微分方程的近似解法都是用一个有限个自由度的系统来代替原来的连续介质系统。在步长为有限值(而非无穷小)情况下的计算稳定性、计算紊乱及计算准确度问题是个有实际重要性问题。本文从物理方面入手讨论这些问题,指出计算紊乱现象或计算不稳定现象是由三种机理造成的:频散效应、能谱非线性转移效应及能量增长效应;指出利用能量守恒方程及正交展开法对于克服计算紊乱现象和提高计算准确度来说可能是较好的。还特别讨论了原始方程的计算困难问题,指出非线性项的计算误差常能激发出强烈的短波长的快波,这是造成计算紊乱的最重要方面。  相似文献   

北斗三频数据的两个无电离层组合轨道钟差估计及其应用     

李杰  张荣之  曾光  龚兵  王冲  房亚男  朱俊  李军锋  强文 《测绘学报》1957,49(11):1377-1387

本文针对全球连续监测评估系统（iGMAS）和国际多系统GNSS试验计划（MGEX）两个观测网接收到不同频率北斗卫星数据的情况,提出了一种北斗卫星（BDS）3个频率（B1I、B2I、B3I）的两种无电离层组合（B1/B3和B1/B2）数据精密定轨（POD）和钟差估计（CE）方法。该方法可以统一处理上述两个观测网收到的北斗二代（BDS-2）,北斗三代试验系统（BDS-3e）和北斗三代全球系统（BDS-3g）3个频率的观测数据,并在一次程序运行中对所有北斗卫星进行联合处理,可有效提高一次运行的数据使用率,从而提高参数估计精度。采集了多天iGMAS、MGEX的GPS和BDS数据进行试验。结果表明,对BDS-3e+BDS-2+GPS联合定轨时,采用三频两组合方法后由于增强了观测几何,BDS轨道重叠RMS为15.9 cm,比传统双频法定轨精度提高11.3%。新方法引入了与卫星端3个频率相关的码偏差,该量多天估计结果稳定,证明了模型和方法可靠。将新方法用于BDS-3g+BDS-3e+BDS-2+GPS联合定轨,6颗BDS-3g的MEO卫星轨道重叠RMS为14.5 cm,钟差重叠RMS为0.43 ns,与BDS-3e的15.1 cm和0.49 ns相当。开展了北斗卫星精密单点定位（PPP）试验,结果显示增加了BDS-3g的6颗MEO的精密轨道和钟差后,测站定位精度水平为39.6 mm,天顶为37.8 mm,比仅用BDS-2和BDS-3e卫星定位精度提高了11.1%。  相似文献   

Statistical analysis of the largest possible earthquake magnitudes on the Ecuadorian coast for selected return periods     

Sandra García-Bustos  Jimmy Landín  Ricardo Moreno  A.S.E. Chong  Maurizio Mulas  Mónica Mite 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2020,14(1):56-68

ABSTRACT

In this work, we have studied the largest earthquake magnitudes on the Ecuadorian coast by using the principles of Extreme Value Analysis based on its two approaches: Block Maxima and Peaks-over-Threshold. First, before modelling the recorded earthquakes, the K-means clustering technique was applied to determine a classification according to the level of magnitude of the earthquakes. Then, models based on the Extreme Value theory of earthquake magnitudes were developed for each of the four clusters that were found, and finally, the best-fitted models were those known as Fréchet and Gumbel ones. The zone with the greatest earthquake magnitudes on the Ecuadorian coast is located between the north of the province of Manabí and the south of the province of Esmeraldas, with a return period of 50 years for an earthquake with magnitude greater than 7.7 M_W.  相似文献   

双阳台DSQ型水管倾斜仪异常分析     

唐春呈  岳冲  张羽  吕晗  李晴晴 《防灾减灾学报》2021,37(3):36-41

双阳地震台DSQ型水管倾斜仪NS分量自2019年10月以来出现加速S倾打破年变形态的异常变化情况.为此对该测项仪器观测状态、观测环境变化、观测台站附近干扰等因素进行科学合理的分析研究,综合分析认为双阳台水管倾斜仪NS分量S倾加速变化为前兆异常.  相似文献   

珠江三角洲都市群城市热岛效应初步研究   总被引：49，自引：8，他引：41  

曾侠  钱光明  潘蔚娟 《气象》2004,30(10):12-15

近十年来 ,珠江三角洲都市群热岛效应全面形成 ,年平均热岛强度由 1 983年前的 0 1℃上升到 1 993年的 0 5℃。珠江三角洲都市群热岛强度呈明显的季节变化和日变化 ,1 1月份热岛强度最强 ,4月份最弱 ,就年平均而言 ,夜间的热岛强度大于白天。珠江三角洲都市群热岛强度空间分布呈中间强周围弱的分布格局 ,与各地的经济活动密切相关 ,热岛强度强的地方均为广东经济活动最活跃的地区。  相似文献   

生态城市空间结构优化组合模式及应用——以襄樊市为例   总被引：15，自引：3，他引：12  

郭荣朝  顾朝林  曾尊固  姜华  张弢 《地理研究》2004,23(3):292-300

在回顾中外生态城市研究进展的基础上 ,提出以人为本 ,自然协调 ;因地制宜 ,规模适度 ;完善高效 ,园林绿化 ;整体协同 ,良性循环等生态城市空间结构优化组合的原则和“绿心组团网络式”城市空间结构模式。并以襄樊市为例进行实证分析。最后结论为生态城市是城市发展的必然趋势 ;构建城市发展引导机制 ,使城市建设逐步转向更加适宜人们居住的生态城市 ;“绿心组团网络式”城市空间结构是比较理想的生态城市空间结构模式之一。  相似文献   

基于OpenGL的地形三维可视化研究   总被引：6，自引：0，他引：6  

曾洪云  孙在宏  乔伟峰 《现代测绘》2003,26(3):29-31

本文利用OpenGL开放图形库的200多个函数,在前人对三维可视化研究的基础上,基于实际生产中的需求,提出一种可行的“二次简化法”,实践证明,这种处理方法能够使生产出的三维地形图在兼顾高度逼真的同时,能够实际地处理空间分析操作运算,满足了生产中的需要。  相似文献   

Application of a “Big-Tree” model to regional climate modeling: a sensitivity study     

X.-M. Zeng  M. Zhao  R.-C. Yu  N.-S. Lin  Y.-Q. Zheng  L.-J. Zhang  R.-J. Zhang 《Theoretical and Applied Climatology》2003,76(3-4):203-218

Summary ¶In order to better understand land-atmosphere interactions and increase the predictability of climate models, it is important to investigate the role of forest representation in climate modeling. Corresponding to the big-leaf model commonly employed in land surface schemes to represent the effects of a forest, a so called big-tree model, which uses multi-layer vegetation to represent the vertical canopy heterogeneity, was introduced and incorporated into the National Center for Atmospheric Research (NCAR) regional climate model RegCM2, to make the vegetation model more physically based. Using this augmented RegCM2 and station data for China during 1991 Meiyu season, we performed 10 experiments to investigate the effects of the application of the big-tree model on the summer monsoon climate.With the big-tree model incorporated into the regional climate model, some climate characteristics, e.g. the 3-month-mean surface temperature, circulation, and precipitation, are significantly and systematically changed over the model domain, and the change of the characteristics differs depending on the area. Due to the better representation of the shading effect in the big-tree model, the temperature of the lower layer atmosphere above the plant canopy is increased, which further influences the 850hPa temperature. In addition, there are significant decreases in the mean latent heat fluxes (within 20–30W/m²) in the three areas of the model domain.The application of the big-tree model influences not only the simulated climate of the forested area, but also that of the whole model domain, and its impact is greater on the lower atmosphere than on the upper atmosphere. The simulated rainfall and surface temperature deviate from the originally simulated result and are (or seem to be) closer to the observations, which implies that an appropriate representation of the big-tree model may improve the simulation of the summer monsoon climate.We also find that the simulated climate is sensitive to some big-tree parameter values and schemes, such as the shape, height, zero-plane displacement height and mixing-length scheme. The simulated local/grid differences may be very large although the simulated areal-average differences may be much lower. The area-average differences in the monthly-mean surface temperature and heat fluxes can amount to 0.5°C and 4W/m², respectively, which correspond to maximum local/grid differences of 3.0°C and 40W/m² respectively. It seems that the simulated climate is most sensitive to the parameter of the zero-plane displacement among the parameters studied.  相似文献   

南方夏季对流云降水回波特征分析   总被引：6，自引：2，他引：4       下载免费PDF全文

李玉林　杨梅曾光平  张国君周益辉　熊华南 《应用气象学报》2003,14(Z1):126-134

利用1988～2000年7～9月南昌、建阳、长沙三站探空资料及同期地面和500 hPa天气图与降雨量资料等,对照1988～2000年7～9月南昌(建阳、长沙713雷达站部分资料)"713"雷达站回波素描图进行统计分析,得出南方夏季对流云回波的顶高、强度、性质等参数变化规律与主要特征,从宏观上了解影响南方夏季对流云回波参数等特征量的变化规律,为南方各省人工影响天气作业提供科学依据.  相似文献   

1303年山西洪洞8级大地震有关问题的讨论     

郭增建  吴瑾冰 《山西地震》2003,(3):31-33,45

用"垂震底继"的准则讨论了1303年和1695年山西2次大地震的关系。指出1303年山西洪洞8级大地震与华北其他8级大震的时间间隔多为25a的倍数。讨论了1303年大震发生的构造条件是块体交界和近于35°纬带。讨论了共轭断层轮换发震观点的困难性。  相似文献