沙尘暴(气体-颗粒)两相流数值模拟-Ⅱ个例分析

利用文献[1]中建立的沙尘暴数值模式,进一步模拟分析了不同沙尘源对我国城市沙尘暴爆发的影响作用。并对 粒子热漂移作用作不同的时间和空间对比分析,得出规律分布曲线。计算结果与我国今年3月18日至21日发生的强沙 尘暴的实况资料进行了比较,证明该模型具有很好的模拟性,模拟结果基本反映了颗粒的分布规律。     

非球形火星沙尘粒子的光谱散射特性研究

针对复杂的火星大气环境,基于T-matrix理论,对三种非球形火星沙尘粒子的散射特性进行了研究,计算了服从对数正态分布的非球形火星沙尘粒子的散射特性,分别在有沙尘暴和无沙尘暴两种条件下,分析非球形火星沙尘粒子的传输衰减和透射率随粒子数浓度、波长以及高度的变化趋势,并与球形粒子进行对比。结果表明:非球形与球形粒子的消光效率因子和散射效率因子存在较大差异,两者之间的最大差值分别为1.786 8和1.761 9,而切比雪夫粒子的散射特性与球形粒子最接近;当入射波长为0.55μm时,火星上沙尘粒子群整体的散射主要集中在前向40°以内,且非球形与球形粒子在前向60°以内散射强度基本相等,大于60°时非球形的散射强度比球形粒子高;非球形火星沙尘粒子的传输衰减和透射率(随波长、粒子数浓度和高度)的变化趋势与球形的基本一致,且其尺寸的比值越接近于1,传输衰减和透射率越接近于球形粒子的值。     

中尺度沙尘暴对量子卫星通信信道的影响及性能仿真

中尺度沙尘暴是美国内华达州、我国北部及中东国家等地沙尘天气的常见形式.为了研究中尺度沙尘暴对量子卫星通信信道的影响,首先分析了沙尘暴的物理特性,根据中尺度沙尘暴的扩散模型,提出了中尺度沙尘特性与量子纠缠度的关系;然后仿真了沙尘特性对量子卫星信道参数的影响.结果表明,如果沙尘扩散时间为12 h,中尺度沙尘粒子半径分别为1和25μm,则量子卫星信道的纠缠度依次为0.6和0.4,信道的利用率分别为0.9和0.8,信道容量分别为0.95和0.8.由此可见,量子信道的各种参数与沙尘暴的特性密切相关.因此,为了提高量子卫星通信的可靠性,应根据沙尘灾变程度,自适应调整卫星信道的各种参数.     

激光雷达观测北京大气气溶胶的垂直分布

利用激光雷达对北京2005年4月26-30日大气气溶胶进行了连续观测,对气溶胶光学特性进行了测量和分析,讨论了大气污染物气溶胶和沙尘气溶胶的垂直分布,以及沙尘气溶胶的传输和沉降过程.因此,激光雷达是研究阴霾天气和沙尘天气特征的有效手段.     

不同模态沙尘暴对太赫兹波的衰减分析

太赫兹波空间传输特性研究对于太赫兹波在空间中的应用具有重要意义.为研究太赫兹波在沙尘暴天气中的传输特性,本文根据沙尘粒子尺度的对数正态分布,应用Mie散射理论和Monte Carlo方法,分析了国内不同地域的六种干沙模态沙尘暴对1—10 THz频段太赫兹波的衰减特性,给出了消光参量和衰减率与频率的关系.结果表明,随着频率的增大,1—10 THz频段太赫兹波的衰减率呈先增加后减小的趋势,沙尘暴的模态不同,太赫兹波衰减较强的频段范围有所不同.为了分析沙粒含水量对太赫兹波传输衰减的影响,计算了不同尺寸的沙尘粒子3个效率因子与含水量的关系,发现粒子尺寸不同,含水量对消光的影响也不同;应用Monte Carlo方法计算了两种湿沙模态的沙尘暴对1—10 THz频段太赫兹波的衰减,给出了衰减率与含水量及频率的关系.结果表明,随沙粒含水量增大,沙尘暴对太赫兹波衰减较强的频段向低频方向移动,含水量小于5%时,太赫兹波衰减率随含水量增大显著增强,湿度较大的沙尘暴天气对太赫兹波的传输衰减影响更大.     

沙尘暴粒子的非球形模型及其对激光的多次散射特性研究

计算沙尘暴对电磁波的衰减特性,以及利用卫星反射率遥感反演沙尘暴的光学厚度时,通常假设沙尘粒子为球形,但实验室和现场测量结果都表明,自然界中的沙尘粒子为非球形,因此利用球形粒子模型模拟沙尘暴对激光的散射和衰减特性将带来较大误差。利用具有一定尺寸分布、形状分布、随机取向的椭球粒子模型模拟自然界中的沙尘粒子,利用T矩阵方法计算了其单次散射特性,并与球形粒子模型进行了比较,结果表明,混合椭球粒子的相函数随角度分布是平滑的、无特征的、且在侧散射方向上是平坦的,这和自然界中的沙尘粒子散射特性非常类似。最后利用累加法计算了沙尘暴对激光的多次散射特性,结果表明,利用任何一种单一形状的粒子模拟沙尘粒子的散射特性都会带来较大的误差。     

蔽日黄沙迥不同 神奇静电匿其中——漫话沙尘中的静电现象

<正>沙尘对人类的危害主要体现在沙尘天气。沙尘天气,是指大量沙或尘被风吹起并随气流进入空中造成大气浑浊的现象。按照能见度(人眼能见的最远距离)大小可分为浮尘(能见度小于10 km)、扬沙(能见度在1~10 km)、沙尘暴(能见度小于1 km)和强沙尘暴(能见度小于500 m)四类。图1展示了国内两城市遭强沙尘暴袭击场景。沙尘天气的危害极其严重,如降低空气质量,毁坏公共设施和农田,影响交通及人类生命安全,导致呼吸系统疾病暴发;影响太     

根据太阳辐射反演沙尘粒子光学厚度个案分析

本文利用邱金桓提出的根据总直接太阳辐射反演0.75微米的气溶胶光学厚度的方法,以2002年3月20日至3月22日发生在我国的沙尘天气为例,使用中国气象局国家卫星气象中心提供的总直接太阳辐射观测资料,以三个观测站点:阿克苏、吐鲁番和福山为例,反演沙尘粒子光学厚度的日变化,并进行了对比检验。结果表明同一地点一天中早晚沙尘粒子光学厚度较小,中午较大;不同地点的沙尘粒子光学厚度随着该地点离沙尘源头的远近而不同,当距离越近时,沙尘粒子光学厚度的值也就越大,反之则越小,这与沙尘粒子迁移性的特点相适应。     

基于AERONET SACOL站观测资料的沙尘气溶胶光学厚度卫星反演试验研究

利用兰州大学大气科学学院半干旱气候变化教育部重点实验室(SACOL站)气溶胶地基观测资料订正出的地表反射率及构建的沙尘气溶胶模型,借助6S大气辐射传输模式,对Terra卫星上的中分辨率成像光谱仪(MODIS)的L1B多光谱资料,进行了沙尘气溶胶光学厚度的个例反演试验。结果表明,四种反演方案的沙尘气溶胶光学厚度的区域分布均比较合理,说明反演方法可行;考虑了波长指数,并用SACOL资料构建的气溶胶模型进行大气订正得出的地表反射率反演出的沙尘气溶胶光学厚度最接近实际测量值,误差为-7.3%。通过对反演过程中的误差进行数值试验检验,结果表明反演方法比较稳定。     

利用紫外Mie散射激光雷达探测澳门地区沙尘暴事件

研制了一台工作波长为355nm的紫外高能Mie散射激光雷达,并利用该激光雷达在2010年一次沙尘暴事件期间对澳门上空的大气进行了探测,得到了澳门地区不同时刻的气溶胶消光系数垂直廓线。利用Fernald方法反演得到的气溶胶近地面消光系数随时间的变化与当地气象数据具有较好的一致性,气溶胶消光系数与当地可吸入颗粒物浓度的相关性达到了0.93。气溶胶垂直廓线显示,在沙尘暴来临期间存在明显的沙尘气溶胶凝集层。通过气溶胶轨迹倒推,分析了沙尘气溶胶的来源及路径。观测结果表明,该激光雷达可以在特殊天气条件下对澳门地区气溶胶进行有效探测,这将有助于深化对澳门上空气溶胶特性的研究。     

The dust emission law in the wind erosion process on soil surface

The dust emission models to date cannot describe the relation between the transport rate of different sized grains and their grain size composition in soil surface, so Aeolian grain transport on a soil-like bed composed of fine sand and silt powder was measured in a wind tunnel. Six types of soil-like beds with different silt fractions have been tested in this experiment. The mass flux profiles of silt dust and sand grains are much different due to their different motion modes. Analysis of the vertical distribution of the powder and sand grains reveals that for a given soil bed, the ratio of the horizontal dust flux to the horizontal sand flux is directly proportional to their mass ratio in the bed. The dust flux is closely linked to the sand flux by the bombardment mechanism. For a given wind velocity and grain size of the bed, the slopes of the vertical mass flux profiles of sand grains larger than 100 μm are nearly equal in a log-linear plot and the ratio between the fraction of transport rate of each size group to the whole transport rate and the mass fraction of each size group in the bed is a constant only dependent on grain size. With this law, the transport rate of dust and different sized grains can be related with the grain size composition in the soil surface. Supported by the National Natural Science Foundation of China (Grant No. 50706031) and the Natural Science Foundation of Shanxi Province of China (Grant No. 2008021005)     

Numerical solution of the radiation transport equation in disk geometry

We describe an efficient numerical method for solving the problem of radiation transport in a dusty medium with two dimensional (2-D) disk geometry. It is a generalization of the one-dimensional quasi-diffusion method in which the transport equation is cast in diffusion form and then solved as a boundary value problem. The method should be applicable to a variety of astronomical sources, the dynamics of which are angular-momentum dominated and hence not accurately treated by spherical geometry, e.g. protoplanetary nebulae, circumstellar disks, interstellar molecular clouds, accretion disks, and disk galaxies. The computational procedure and practical considerations for implementing the method are described in detail. To illustrate the effects of 2-D radiation transport, we compare some model results (dust temperature distributions and i.r. flux spectra) for externally heated, interstellar dust clouds with spherically symmetric and disk geometry.     

Large-Scale Transport of Charged Macroparticles Induced by Dust–Acoustic Solitons

We have studied experimentally the oscillatory process in the dusty plasma in the glow discharge stratum. It is shown that the oscillations are induced by the dust–acoustic instability, as a result of which dust–acoustic solitons are excited. The motion of dust particles in the electric field of solitons has been analyzed. It has been established that a soliton leads to a large-scale unidirectional transport of charged particles in the direction of its motion. The experimental results have been interpreted theoretically using the MHD model of the plasma.     

Stable dust structures in non-self-sustained gas discharge under atmospheric pressure

The formation of stable dust structures in electron-beam-controlled non-self-sustained discharge plasma was predicted and experimentally observed. To determine the conditions for dust-particle levitation, the self-consisted one-dimensional simulation of a non-self-sustained gas discharge was carried out using a nonlocal model of charged plasma-particle transport with allowance for electron diffusion. It is shown that, in the cathode layer of a non-self-sustained gas discharge, a strong electric field arises in the Thomson regime, which, in conjunction with the gravity force, forms a potential well where the dust particles undergo levitation.     

Nonlinear dynamics of surface dust vortex and dust zonal flow systems

We present analytical and simulation studies of highly resolved dust fluid flows involving nonlinearly coupled incompressible surface dust vortex modes (SDVMs) and dust zonal flows (DZFs) in nonuniform unmagnetized dusty plasmas. For this purpose, we use the hydrodynamic equations for the dust fluid and Boltzmann distributed electrons and ions and obtain a set of equations that exhibit nonlinear couplings between the SDVMs and DZFs. The nonlinear equations are then used to investigate the parametric excitation of DZFs by the Reynolds stresses of the SDVMs. Large scale SDVMs emerge through nonlinear interactions with DZFs, and they suppress the dust particle transport across the density gradient. In contrast, DZFs possess short scale vortices with a higher turbulent transport. The relevance of our investigation into the role of coherent structures in a nonuniform dusty plasma is discussed.     

Optoheterodyne Doppler measurements of the ballistic expansion of the products of the shock wave-induced surface destruction: Experiment and theory

The results of optoheterodyne Doppler measurements of the ballistic expansion of the products of surface destruction under shock-wave loading are presented. The possibility of determining the physical characteristics of a rapidly flying dust cloud, including the microparticle velocities, the microparticle sizes, and the areal density of the dust cloud, is shown. A compact stand for performing experiments on shock-wave loading of metallic samples is described. Shock-wave loading is performed by a 100-µm-thick tantalum flyer plate accelerated to a velocity of 2.8 km/s. As the samples, lead plates having various thicknesses and the same surface roughness are used. At a shock-wave pressure of 31.5 GPa, the destruction products are solid microparticles about 50 µm in size. At a pressure of 42 and 88 GPa, a liquid-drop dust cloud with a particle size of 10–15 µm is formed. To interpret the spectral data on the optoheterodyne Doppler measurements of the expansion of the surface destruction products (spalled fragments, dust microparticles), a transport equation for the function of mutual coherence of a multiply scattered field is used. The Doppler spectra of a backscattered signal are calculated with the model developed for the dust cloud that appears when a shock wave reaches the sample surface at the parameters that are typical of an experimental situation. Qualitative changes are found in the spectra, depending on the optical thickness of the dust cloud. The obtained theoretical results are in agreement with the experimental data.     

Distribution of charged lunar dust in the south polar region of the moon

Lunar dust is one of the most threatening problems confronting the return of human beings to the moon. In this work we studied the spatial distribution behavior of charged lunar dust in the solar wind plasma environment in the south polar region of the moon and considered the influence of a mini-crater using Spacecraft Plasma Interactions Software. The distribution of dust and plasma at low solar altitude angles of 20° and 0° was studied, and the spatial density of lunar dust was ~10^10.4 m^-3 and ~10^11.5 m^-3, respectively. This is because a higher surface potential will result in transportation of small dust particles and photoelectrons can also neutralize positively charged lunar dust. The dust density in the plasma void region created by a mini-crater with a 5 m high wall was studied. We obtained a quasi-neutral electric environment in the plasma void region of the mini-crater, and the dust density was about a magnitude lower than that in other regions. The dust risk to a spacesuit is much lower on the nightside than on the dayside, but there is severe charged lunar dust transport in the region between light and shade, which is dominated by the difference in surface and plasma potential caused by photoelectrons.     

Full-torus impurity transport simulation for optimizing plasma discharge operation using a multi-species impurity powder dropper in the large helical device

The transport of impurities supplied by a multi-species impurity powder dropper (IPD) in the large helical device (LHD) is investigated using a three-dimensional peripheral plasma fluid code (EMC3-EIRENE) coupled with a dust transport simulation code (DUSTT). The trajectories of impurity powder particles (Boron, Carbon, Iron, and Tungsten) dropped from the IPD and the impurity transport in the peripheral plasma are studied in a full-torus geometry. The simulation reveals an appropriate size of the impurity powder particles and an optimum operational range of the dust drop rates for investigating the impurity transport without inducing radiation collapse. The simulation also predicts a favourable plasma discharge condition for wall conditioning (boronization) using the IPD in order to deposit boron to high plasma flux and neutral particle density areas in the divertor region in the inboard side of the torus.     

剖面不变性与托卡马克放电中的

从通常的局部输运模型的角度分析,托卡马克等离子体中有相当多的输运现象会被视为“奇怪”的或“反常”的,即难于被正确的理解,也难于给出统一的描述方式。基于温度剖面不变性的－－这里称炎这相容模型的描述方法,在不涉及非局部输运任何具体物理机制的情况下,给出了包含非局部效应的热导系数及其与局部反常热导系数的关系。利用这种相容热导模型统一地描述并分析了一些看似奇怪或反常的输运现象。