Light Scattering by Dust Under Microgravity Conditions

Most of our knowledge on heterogeneous media in the Universe comes from the light they scatter. This light is mainly linearly polarized, and the polarization phase curves contain information about the properties of the scattering dust. In the solar system, the dust seems to be made of irregular aggregates with a size greater than a few microns and a fractal structure. Many constraints appear in the scattering computations, due to the trickiness of the mathematical calculations, and to our ignorance of the precise structure of the dust. This leads to the necessity to perform light scattering measurements on characteristic aggregates, built under low velocity ballistic collisions. Microgravity is a sensible way to achieve such measurements on a cloud of levitating and aggregating dust particles. A first step has been the PROGRA² experiment, which operates during parabolic flights on an aircraft. The instrument is a polar nephelometer measuring successively the light scattered by a dust sample at various angles; it is fully operational, and will provide a data base of polarization phase curves. A second step is the CODAG-SR experiment, which uses the duration of a rocket flight to build up dust aggregates. The instrument measures simultaneously the light scattered at numerous phase angles; it is now space qualified, and should provide in a near future a monitoring of the intensity and polarization phase curves while the aggregation processes are taking place. This revised version was published online in July 2006 with corrections to the Cover Date.     

陕西气溶胶总悬浮颗粒物来源解析

使用受体数学模型中的化学元素平衡法（ＣＥＢ）对西安市３个不同地点和枣园大气气溶胶进行来源解析,以表明陕西地区气溶胶来源的总体水平。结果显示,土壤尘占３５％～６０％,煤烟尘占１５％～３０％,建筑尘占１５％～２５％,冶炼尘占４％～１５％。各源贡献率的差异与工业排放和人类活动很好一致     

平流层气溶胶的辐射强迫及其气候响应的水平二维分析

利用比较先进的辐射模式计算了平流层气溶胶的辐射强迫,并对之进行了参数化。结果发现平流层气溶胶的辐射强迫的水平分布不仅与其本身的水平变化有关,而且与下垫面的反照率有很大的关系。利用近期开发的二维能量平衡模式模拟了皮纳图博火山气溶胶对地面平衡温度的影响,结果表明:皮纳图博火山至喷发后1年半左右降温达最大,至喷发后第5年降温已很小。     

2001年春季中国北方大气气溶胶光学厚度与沙尘天气

利用敦煌、北京等5个观测站的大气光学厚度[AOT(λ)]资料，分析了2001年春季中国北方大气气溶胶光学厚度的时空分布特征。结果表明，在观测期内各站每月都有大气气溶胶光学厚度高值[AOT(λ＝0．50μm)≥1．04]出现，与我国北方历年在春季发生的沙尘天气的一般时空分布特征基本一致。本文还探讨了大气气溶胶光学厚度与水平能见度以及沙尘天气之间的关系。     

河西走廊强和特强沙尘暴变化趋势的初步研究

分析了河西走廊1955—2000年强和特强沙尘暴的气候变化。研究表明，河西走廊强和特强沙尘暴自1955年以来主要呈下降趋势；但是从20世纪90年代末期起，有增多的趋势。20世纪50年代和70年代偏多，60年代正常，80年代偏少，90年代最少。强和特强沙尘暴的突变年份出现在60年代后期和1980年前后。     

腾格里沙漠气溶胶光学厚度多波段遥感研究

根据2001年4～9月份在腾格里沙漠沙坡头站进行的为期6个月的地面多波段太阳直接辐射观测结果，讨论了仪器的定标、气溶胶的不同波段光学厚度及其变化规律。结果表明，仪器的定标合理；腾格里沙漠地区的气溶胶光学厚度在不同天气状况下的变化有很大差别，而总体光学厚度较大，时空变化较大；但在同等条件下，各波段变化规律基本一致；不同天气状况下存在不同的气溶胶分布特征。     

极地雪冰中表征大气浊度的微粒和各类污染物

全球气候变化和环境问题是当代人们共同关注的热点。两极地区在地理上具有特殊性 ,其大气和冰芯的微粒记录包含了火山 ,沙尘暴以及人类活动等特殊事件的信息。本文在总结前人研究的基础上 ,重点讨论了硫化物、碳黑、氮氧化物及硝酸盐、有机污染物以及重金属等大气中与人类活动密切相关的微粒物质     

2002年我国沙尘暴的若干特征分析

利用2002年的地面观测资料和NCEP/NCAR的再分析资料对2002年3、4月沙尘暴发生频率以及相应的月和候的环流形势特征进行了分析。结果表明，东亚大槽发展和加深是造成该年沙尘暴偏北路径多的主要成因，并且是影响华北、东北甚至华中的一种主要环流形势。东北低涡维持期间生成的副冷锋次天气尺度系统，可以产生强局地沙尘暴。使用GMS-5的卫星观测资料的亮温数据，对沙尘暴在冷涡天气下的沙尘输送情况进行了分析。给出了沙尘暴在向下游输送沙尘时的空间分布，特别指出了在东北冷涡强烈发展的形势下，沙尘可以向东北方向输送，影响东北、远东，甚至更北的地区。     

AN ANALYSIS OF THE AEROSOLS IN THE LOWER-LEVEL ATMOSPHERE OVER BEIJING NORTHERN SUBURBS IN WINTER*

The physical and chemical characteristics of the aerosol samples were studied.The samples were collected on the 3 platforms (at levels 8 m,100 m and 320 m respectively) of IAP (Institute of Atmospheric Physics,Chinese Academy of Sciences) observation tower during the periods from January 1 to 16 and from February 20 to March 2,2001.The concentrations of TSP (total suspended particles),chemical components and size distribution for aerosols were calculated.The effects of the meteorological conditions on the aerosol concentrations and its distributions werestudied.The main aerosol sources from which the aerosols in the samples collected came were investigated.The conclusion was drawn preliminarily as follows.The TSP concentrations decreased with height.Over 70% of the aerosol mass were distributed in the fine particle group (d<2.1μm).The top 20 aerosol elements with high concentration are listed from high to low according to their concentrations,and they are S,Fe,Ca,K,A1,Na,Mg,Zn,Cl,Ba,P,Ti,Pb,Mn,As,Cu,V,Br,Cr,and Sb.The aerosol element concentrations decreased with height,too.The mass of volatile elements was mainly distributed in the fine particle group.The ion mass was distributed in the same way as the element mass.From the point of view of contribution to the air aerosols,both anthropogenic and natural sources are important for Beijing.     

Unprecedented last-glacial mass accumulation rates determined by luminescence dating of loess from western Nebraska

A high-resolution chronology for Peoria (last glacial period) Loess from three sites in Nebraska, midcontinental North America, is determined by applying optically stimulated luminescence (OSL) dating to 35–50 μm quartz. At Bignell Hill, Nebraska, an OSL age of 25,000 yr near the contact of Peoria Loess with the underlying Gilman Canyon Formation shows that dust accumulation occurred early during the last glacial maximum (LGM), whereas at Devil’s Den and Eustis, Nebraska, basal OSL ages are significantly younger (18,000 and 21,000 yr, respectively). At all three localities, dust accumulation ended at some time after 14,000 yr ago. Mass accumulation rates (MARs) for western Nebraska, calculated using the OSL ages, are extremely high from 18,000 to 14,000 yr—much higher than those calculated for any other pre-Holocene location worldwide. These unprecedented MARs coincide with the timing of a mismatch between paleoenvironmental evidence from central North America, and the paleoclimate simulations from atmospheric global circulation models (AGCMs). We infer that the high atmospheric dust loading implied by these MARs may have played an important role, through radiative forcing, in maintaining a colder-than-present climate over central North America for several thousand years after summer insolation exceeded present-day values.