地形追随坐标系下埃特尔位涡的计算

随着数值天气预报模式的日益普及以及位涡在不同天气、气候时、空尺度上的广泛应用,对采用模式输出资料计算的埃特尔（Ertel）位涡的精度提出了更高要求。将气象要素从中尺度模式普遍采用的地形追随坐标系向定义位涡的z或p坐标系的插值过程（插值法）,是导致埃特尔位涡计算误差的主要原因。文中利用地形追随坐标系与z（p）坐标系的变换关系,导出了z坐标系定义的埃特尔位涡在地形追随坐标系中的表达形式,实现了直接在模式格点上计算埃特尔位涡（直接法）,在提高计算精度的同时,保留了其在z坐标系中的物理意义,方便了分析与应用。为了进一步分析直接法在减少计算误差方面的作用,使用WRF模式对2016年7月发生在华北地区复杂地形背景下的一次黄淮气旋爆发过程进行了模拟,利用模式输出资料对此次天气过程中强降水时段插值法计算误差的分布进行了分析。结果表明,利用直接法计算位涡可有效减少插值法引入的计算误差,中低层均方根误差可达0.5 PVU,中高层可达0.3 PVU。将其应用到中小尺度对流性天气精细化结构的分析及气候统计研究中,可以有效减少插值法误差对结果产生的不良影响,提高计算和分析准确度。      

拨地工程坐标成果的自动化输出

使用AutoCAD软件来计算拨地工程的坐标成果较传统计算器人工计算是一个巨大的进步,即便如此,当遇到包含多个地块的拨地工程时,逐个地块完成计算并填写成果表格,工作量仍然很大,而且对于作业过程中局部小的调整还要进行大量重复工作,并且人工干涉多,容易出现纰漏。本文介绍利用自动搜索封闭地块多边形的图形算法,实现拨地工程地块坐标成果的自动化输出,从根本上解决了传统方法效率低、人工干涉多、易出错等问题。     

自然灾害风险地图中的制图综合研究——以点状承灾体为例

为提高多尺度灾害风险地图表达中高风险区承灾体的准确、有效、快速识别,基于灾害风险理论,运用地理学规律,在GIS等技术支持下,结合数据挖掘和空间分析技术,探讨了在尺度转换过程中点状承灾体的制图综合问题,并结合承灾体自身及在灾害系统中的属性特征,抽象概括了点状承灾体在灾害地图中的制图综合类型,即重要性综合、特殊性综合、邻近性综合、条件性综合、完整性综合、随机性综合。针对每一种综合类型,给出了可能的灾害情景假设及制图综合方法,并进行了技术实现及可视化表达。结果表明,基于上述6种类型的点状承灾体制图综合,不仅有效解决了尺度转换过程中的数据冗余问题,而且还能准确反映出特定孕灾环境下高风险区承灾体的空间分布,同时也为灾害风险地图的制图综合提供一种新的思路。本研究为区域灾害风险识别、风险防范与管理提供理论与技术支持,进而为区域的防灾减灾提供科学依据。     

Dynamic model of mesoscale eddies. Eddy parameterization for coarse resolution ocean circulation models

In the framework of the eddy dynamic model developed in two previous papers (Dubovikov, M.S., Dynamical model of mesoscale eddies, Geophys. Astophys. Fluid Dyn., 2003, 97, 311–358; Canuto, V.M. and Dubovikov, M.S., Modeling mesoscale eddies, Ocean Modelling, 2004, 8, 1–30 referred as I–II), we compute the contribution of unresolved mesoscale eddies to the large-scale dynamic equations of the ocean. In isopycnal coordinates, in addition to the bolus velocity discussed in I–II, the mesoscale contribution to the large scale momentum equation is derived. Its form is quite different from the traditional down-gradient parameterization. The model solutions in isopycnal coordinates are transformed to level coordinates to parameterize the eddy contributions to the corresponding large scale density and momentum equations. In the former, the contributions due to the eddy induced velocity and to the residual density flux across mean isopycnals (so called Σ-term) are derived, both contributions being shown to be of the same order. As for the large scale momentum equation, as well as in isopycnal coordinates, the eddy contribution has a form which is quite different from the down-gradient expression.     

自动制图综合中的线目标位移模型

数字地图制图环境下的自动综合是一个国际性的难题,其中地图要素的关系处理又是自动综合中的重点和难点之一,位移操作是关系处理的一个重要方法.本文以道路网的目标变形位移运用弹性力学思想进行理论和方法上的探讨,实现空间目标冲突的探测,进行目标的受力分析,运用平面杆件弹性体的受力变形模型,得到目标的位移量.该方法顾及目标间的空间关系,运用优化方法解决和控制位移的传播.     

线状要素与面状要素的关系处理

线状要素与面状要素的关系在地图制图综合中是必须处理的。它们的关系在制图综合和景观模型向制图模型的转换中都是必须考虑的。本文主要讨论线状要素与面状要素的关系以及这些关系在数据处理中的保持。     

多波束数据处理中的UTM直角坐标与经纬度坐标转换技术

简要介绍了地图投影的一般概念,重点描述了UTM的优点及其与大地坐标之间的相互转换,该转换方法软件化后形成的技术可以为多波束数据后处理商业软件提供坐标转换的补丁技术。最后附上部分经实际检验的Fortran程序供参考。     

Energetics of lateral eddy diffusion/advection：Part Ⅱ. Numerical diffusion/diffusivity and gravitational potential energy change due to isopycnal diffusion

Study of oceanic circulation and climate requires models which can simulate tracer eddy diffusion and ad vection accurately. It is shown that the traditional Eulerian coordinates can introduce large artificial hori zontal diffusivity/viscosity due to the incorrect alignment of the axis. Therefore, such models can smear sharp fronts and introduce other numerical artifacts. For simulation with relatively low resolution, large lateral diffusion was explicitly used in models; therefore, such numerical diffusion may not be a problem. However, with the increase of horizontal resolution, the artificial diffusivity/viscosity associated with hori zontal advection in the commonly used Eulerian coordinates may become one of the most challenging ob stacles for modeling the ocean circulation accurately. Isopycnal eddy diffusion （mixing） has been widely used in numerical models. The common wisdom is that mixing along isopycnal is energy free. However, a careful examination reveals that this is not the case. In fact, eddy diffusion can be conceptually separated into two steps： stirring and subscale diffusion. Due to the thermobaric effect, stirring, or exchanging water masses, along isopycnal surface is associated with the change of GPE in the mean state. This is a new type of instability, called the thermobaric instability. In addition, due to cabbeling subscale diffusion of water parcels always leads to the release of GPE. The release of GPE due to isopycnal stirring and subscale diffusion may lead to the thermobaric instability.     

地心坐标反解大地坐标的非线性方程组牛顿迭代法分析

目前的一些地心坐标向大地坐标的转换模型在计算速度,稳定性或精度方面存在一定的局限性。本文探讨了非线性方程组数值迭代的求解方法及其在MATLAB 7.0中的编程实现,并将结果与基于一元三次方程求解的严密方法做了比较分析,结果证明该方法是可以在实际中参考应用的。     

Qualitative and quantitative analysis of vorticity,strain and area change in general non-isochoric 2D deformation

A scale free representation of a general non-isochoric 2D deformation is presented which is amenable to mathematical analysis. By describing deformation in 2D in terms of polar coordinates the stretching and rotational histories of linear elements separate and are easily analysed both qualitatively and quantitatively. An analysis of finite strain combined with dynamical considerations allows the derivation of equations which may be used to estimate finite strain, area change and kinematic vorticity number. Numerical investigation of method developed here was carried out and it was found to perform well unless large area changes occur in combination with large components of simple shear. A re-analysis of natural data indicates the method is consistent.