稳健加权总体最小二乘的点云数据平面拟合

针对观测向量和系数矩阵均含有误差以及点云数据存在异常点的问题,该文提出一种稳健加权总体最小二乘法。该方法在加权总体最小二乘的基础上,通过设置一定的准则,剔除点云数据中存在的异常点,以获取更为精确的平面拟合参数解。仿真模拟算例和实际点云数据实验结果表明,该方法与传统的方法相比,能够消除异常点带来的影响,获得更精确的参数解,平面拟合精度更高。     

Using modular 3D digital earth applications based on point clouds for the study of complex sites

This article discusses the use of 3D technologies in digital earth applications (DEAs) to study complex sites. These are large areas containing objects with heterogeneous shapes and semantic information. The study proposes that DEAs should be modular, have multi-tier architectures, and be developed as Free and Open Source Software if possible. In DEAs requiring high reliability in the 3D measurements, point clouds are proposed as basis for the 3D Digital digital earth representation. For the development of DEAs, we propose to follow a workflow with four components: data acquisition and processing, data management, data analysis and data visualization. For every component, technological challenges of using 3D technologies are identified and solutions applied for a case study are presented. The case study is a modular 3D DEA developed for the archaeological project Mapping the Via Appia. The 3D DEA allows archaeologists to virtually analyze a complex study area.     

Comparisons of sulfate and nitrate production in clouds on the mid-Atlantic and Pacific Northwest Coasts of the United States

Measurements are presented of sulfate and nitrate production in clouds on the East and West coasts of the United States. Sulfate production measured on the mid-Atlantic Coast was significantly greater than on the Pacific Northwest Coast. Nitrate production was significant on the mid-Atlantic Coast but, on average, insignificant on the Pacific Northwest Coast. Measurements of sulfate and nitrate scavenging coefficients by clouds are also presented.     

A reliable and efficient two-stream algorithm for spherical radiative transfer: Documentation of accuracy in realistic layered media

We present a fast and well documented two-stream algorithm for radiative transfer and particle transport in vertically inhomogeneous, layered media. The physical processes considered are internal production (emission), scattering, absorption, and Lambertian reflection at the lower boundary. The medium may be forced by internal sources as well as by parallel or uniform incidence at the top boundary. This two-stream algorithm is based on a general purpose multi-stream discrete ordinate algorithm released previously. It incorporates all the advanced features of this well-tested and unconditionally stable algorithm, and includes two new features: (i) corrections for spherical geometry, and (ii) an efficient treatment of internal sources that vary rapidly with depth. It may be used to compute fluxes, flux divergences and mean intensities (actinic fluxes) at any depth in the medium. We have used the numerical code to investigate the accuracy of the two-stream approximation in vertically inhomogeneous media. In particular, computations of photodissociation and warming/cooling rates and surface fluxes of ultraviolet and visible radiation for clear, cloudy and aerosol-loaded atmospheres are presented and compared with results from multi-stream computations. The O₃ +hv O(¹D) + O₂ and O₃ +hv O(³P) + O₂ photodissociation rates were considered for solar zenith angles between 0.0–70.0° and surface albedos in the range 0.0–1.0. For small and moderate values of the solar zenith angle and the surface albedo the error made by the two-stream approximation is generally smaller, <10%, than the combined uncertainty in cross sections and quantum yields. Surface ultraviolet and visible fluxes were calculated for the same range of solar zenith angles and surface albedos as the photodissociation rates. It was found that surface ultraviolet and visible fluxes may be calculated by the two-stream approximation with 10% error or less for solar zenith angles less than 60.0° and surface albedos less than 0.5. For large solar zenith angles and/or large surface albedos, conditions typical at high latitudes, the error made by the two-stream approximation may become appreciable, i.e. 20% or more for the photodissociation rates in the lower stratosphere and for ultraviolet and visible surface fluxes for large surface albedos. The two-stream approximation agrees well with multi-stream results for computation of warming/cooling rates except for layers containing cloud and aerosol particles where errors up to 10% may occur. The numerical code provides a fast, well-tested and robust two-stream radiative transfer program that can be used as a software tool by aeronomers, atmospheric physicists and chemists, climate modellers, meteorologists, photobiologists and others concerned with radiation or particle transport problems. Copies of the FORTRAN77 program are available to interested users.     

新疆巴州“6.4”罕见大暴雨中尺度特征分析

利用FY卫星、新一代天气雷达、区域自动站及GFS/NCAR 0.5°×0.5°再分析资料,对2012年6月4日发生在新疆巴音郭楞蒙古自治州境内的一次罕见大暴雨进行中尺度特征分析。分析结果表明:(1)高空冷槽是主要影响系统,地面中尺度辐合中心和中尺度切变线等中尺度天气系统与大暴雨的形成和分布关系密切。(2)显著的不稳定能量是产生暴雨的重要因素,特殊的地形对水汽辐合抬升起到了关键作用。(3)暴雨发生在MCS中云顶亮温小于-55℃且长时间维持的冷云盖边缘。人字形回波头部、逗点云尖点处长时间维持50 d Bz以上的多单体风暴是形成大暴雨的主要原因。     

The Effect of the Sea-ice Zone on the Development of Boundary-layer Roll Clouds During Cold Air Outbreaks

High latitude air–sea interaction is an important component of the earth’s climate system and the exchanges of mass and energy over the sea-ice zone are complicated processes that, at present, are not well understood. In this paper, we perform a series of numerical experiments to examine the effect of sea-ice concentration on the development of high latitude boundary-layer roll clouds. The experiments are performed at sufficiently high spatial resolution to be able to resolve the individual convective roll clouds, and over a large enough domain to be able to examine the roll’s downstream development. Furthermore the high spatial resolution of the experiments allows for an explicit representation of heterogeneity within the sea-ice zone. The results show that the sea-ice zone has a significant impact on the atmospheric boundary-layer development, which can be seen in both the evolution of the cloud field and the development of heat and moisture transfer patterns. In particular, we find the air-sea exchanges of momentum, moisture and heat fluxes are modified by the presence of the roll vortices (typically a 10% difference in surface heat fluxes between updrafts and downdrafts) and by the concentration and spatial distribution of the sea-ice. This suggests that a more realistic representation of processes over the sea-ice zone is needed to properly calculate the air-sea energy and mass exchange budgets.     

Turbulent and Thermodynamic Structure of the Autumnal Arctic Boundary Layer Due to Embedded Clouds

We have studied the role of low-level clouds in modifying the thermodynamic and turbulence properties of the Arctic boundary layer during autumn. This was achieved through detailed analyses of boundary-layer properties in two regions, one with low-level cloud cover and the other free of clouds, using measurements from a research aircraft during the Beaufort and Arctic Storms Experiment (BASE). Both regions were measured on the same day under similar synoptic forcing. The cloudy region was characterized by strong horizontal inhomogeneity in low-level temperature and moisture that varied with the cloud-top height. The clear region was relatively homogeneous in temperature and specific humidity with a strong temperature inversion extending between heights of 100 m and 3 km. From measurements at the lowest levels, we also identified a shallow mixed layer below the deep stable layer in the clear region.Our spectral analyses revealed significant modifications of boundary-layer properties due to the presence of low-level clouds. In the cloudy region, turbulent perturbations dominated the boundary-layer flow and made large contributions to the scalar variances. In the clear boundary-layer, wave motion contributed significantly to the observed variances, while turbulent flow was relatively weak. The clear region was saturated, although no detectable clouds were measured.     

混合相层状云系模式和中尺度低涡云系的实例模拟

在Ａｎｔｈｅｓｅｔａｌ．的中尺度模式基础上引入胡志晋的双参数层状云模式并重新编制了程序，构成一个包含三种水相态和比较详细云物理过程的三维层状云系模式。为保持在较长时步中计算的稳定和精度，对微物理过程的计算采用混合格式，少数过程采用时间分裂格式，在相变过程的处理上设计了同时计算不同相态相变的参数化方案，按Ｌａｇｒａｎｇｉａｎ方法设计了粒子下落格式。用干模式、积云参数化模式、两相显式模式和本文模式对两个中尺度低涡个例作了模拟，对比分析不同模式的模拟能力。结果表明本文模式对涡环流结构、云场和降水分布的摸拟比其他模式更合理，更接近实况。