A model for solar quiet day variation at low latitude from past observations using singular spectrum analysis

Singular spectrum isolates significant principal components in a time series from the embedded noise. This tool-kit is used to reconstruct trend-free individual time series, formed by restricting the mean monthly hourly values of geomagnetic field to one hour at a time at a low latitude station Alibag (dipole latitude 9.5°N). Each reconstructed component is extrapolated over the next 12 values using an autoregressive model based on Burg’s maximum entropy algorithm. Details of a numerical approach to increase the reliability of extrapolation are highlighted. The extrapolated reconstructed components are then combined to generate predicted monthly values for each hour. The mean diurnal variation for any month obtained from the extrapolated individual hourly time series compares favorably with the observations. This approach to Sq(H) modelling incorporating both long and short term variations will be beneficial in the derivation of Dst index.     

GIS制图中标准图框的机助生成

主要介绍了我国基本比例尺地形图的分幅与编号以及机助生成标准图廓（标准图框）的数学基础和生成过程,最后还简要地介绍了ＭＡＰＧＩＳ标准图框生成程序及其应用．     

全球低纬高原地区气候特征的初步研究

提出了全球１０大低纬高原和２０个著名春城的概念,给出了３５个有代表性的低纬高原气象站资料,通过分析气温和降水变化,得到低纬高原气候的共同特征是气温年较差小,四季如春,气温日较差大,一天分四季,降水适中,干湿季分明。主要气候类型是热带草原气候和高原型季风气候     

低磁纬度区航磁异常变倾角磁方向转换方法

本文给出了几种适用于低磁纬度区的变倾角磁方向转换方法，在理论模拟及实际资料处理中均获得良好效果。     

关于低纬边界层顶垂直速度的计算

提出了一个由低纬地（海）面风计算边辊层顶垂直速度的方法，得到了低纬边界层顶生趣速度的一些特征，指出了惯性项及β效应的重要作用。     

行星际磁场扇形结构对中低纬地磁场的影响

本文用特征向量分析法对1973年北京地磁台水平磁场强度H的时均值资料进行了研究,识别出了行星际磁场扇形效应对中低纬地磁场H日变化的贡献。研究结果表明,中低纬扇形效应约为3-5nT的数量级,分点月最大（～5nT）,冬季最小（～3nT）。当扇形磁场背离太阳时,扇形效应引起白天H增大,夜间减小;当扇形磁场朝向太阳时,H的变化相反。用第一特征向量推断行星际磁场的扇形极性,其符合率在两分点月份和夏季达到70％左右,冬季低于50％,暗示了冬季反向扇形效应的存在。     

Characterization and reconstruction of a rock fracture surface by geostatistics

It is well understood that, in studying the mechanical and hydromechanical behaviour of rock joints, their morphology must be taken into account. A geostatistical approach has been developed for characterizing the morphology of fracture surfaces at a decimetre scale. This allows the analysis of the spatial variability of elevations, and their first and second derivatives, with the intention of producing a model that gives a numerical three‐dimensional (3D) representation of the lower and upper surfaces of the fracture. Two samples (I and II) located close together were cored across a natural fracture. The experimental data are the elevations recorded along profiles (using recording steps of 0.5 and 0.02 mm, respectively, for the samples I and II). The goal of this study is to model the surface topography of sample I, so getting estimates for elevations at each node of a square grid whose mesh size will be, for mechanical purposes, no larger than the recording step. Since the fracture surface within the sample core is not strictly horizontal, geostatistical methods are applied to residuals of elevations of sample I. Further, since structural information is necessary at very low scale, theoretical models of variograms of elevations, first and second derivatives are fitted using data of both that sample I and sample II. The geostatistical reconstructions are computed using kriging and conditional simulation methods. In order to validate these reconstructions, variograms and distributions of experimental data are compared with variograms and distributions of the fitted data. Copyright © 2002 John Wiley & Sons, Ltd.     

2009号台风“美莎克”对黑龙江的影响及非对称结构特征

使用常规观测资料及ERA5（0.25°×0.25°）再分析资料,对2009号台风“美莎克”进行分析。结果表明：此次过程,副热带高压异常强大,位置偏北,并与北侧阻高合并形成高压坝阻挡;“美莎克”沿副高外围北上与中纬度低涡及冷空气相互作用,变性后斜压性明显加大,低涡增强;“美莎克”携带大量水汽,同时中低空急流将海上水汽持续向黑龙江输送,并在黑龙江强烈辐合,形成强的水汽辐合区和水汽辐合带;高低空急流耦合构成强的垂直环流,对应非常强的垂直上升速度;副热带高压向西北伸展,高空引导气流和热成风方向转为西北—东南向,促使“美莎克”登陆后向西北移动,穿过黑龙江,是黑龙江出现大暴雨的主要原因。分析台风中心涡度、散度、垂直速度、位温、湿位涡等物理量的三维结构变化,可以很好地认识台风在北上登陆中的变性过程以及降水出现非对称结构的原因。     

椭球情形下等角和等面积正圆柱投影间的直接变换

为实现椭球情形下等角和等面积圆柱投影间的直接变换,借助具有强大符号运算功能的计算机代数系统Mathematica,推导出了等量纬度和等面积纬度函数间变换的直接展开式,并将公式系数统一表示为椭球第一偏心率e的幂级数形式,且统一展开至e~(10)。在此基础上建立了等角和等面积正圆柱投影间的直接变换模型,可解决不同参考椭球下的投影变换问题。精度比对结果表明本文建立的直接变换模型相比于传统间接变换模型精度提高3～5个数量级,完全可以满足地图海图制图精密计算的需要。     

等角纬度与子午线弧长变换的直接表达式

为了便于实现等角方位投影与椭球等距离圆柱或圆锥投影之间的变换,借助具有强大符号运算功能的计算机代数系统Mathematica,推导出了等角纬度和子午线弧长之间变换的直接表达式,进一步将表达式改进为适合电算的形式,并将其系数统一表示为关于椭球偏心率e和椭球第三扁率n的幂级数形式。通过算例分析表明:基于第三扁率n的幂级数表达式具有更紧凑的形式和更好的收敛性,且导出公式的计算误差分别小于10^-7″和10^-8m,可以满足大地测量和地图制图计算精度要求。