东亚地区矿物尘气溶胶直接辐射强迫的初步模拟研究

为研究东亚地区矿物尘气溶胶的直接辐射效应,在区域气候模式RegCM3中加入起尘方案、建立矿物尘气溶胶输送模式,并将其辐射过程加入区域气候模式的辐射方案.通过对2001年3月～2002年3月的模拟发现：中国西北和蒙古国年平均地表起尘率在1μg/(m2·s)以上,最大达到90μg/(m2·s)是东亚地区最主要的矿物尘气溶胶源地;东亚地区矿物尘气溶胶柱含量最大值达5g/m2,出现在塔克拉玛干沙漠和秦岭地区;气溶胶大气顶直接辐射强迫基本呈现大陆上为正、海洋上正负均有的分布特征,区域平均辐射强迫在春夏秋冬分别为108, 088, 037,040W/m2,短波辐射强迫在陆上为正、海上正负均有,长波辐射强迫均为正值;四季的地表辐射强迫分别为-564, -225, -137, -187W/m2;辐射强迫数值对矿物尘气溶胶单次散射反照率的变化较敏感.     

Estimation of areas of sand and dust emission in the Hexi Corridor from a land cover database: an approach that combines remote sensing with GIS

The present study combined remote sensing with geographical information system (GIS) technology to interpret Landsat TM images from 1996 to 2000 and establish a land cover database for the Hexi Corridor of China’s Gansu Province. The areas of sand and dust emission and trends in their change were extracted by analyzing the database, with the following results: In 2000, the source area for sand and dust storms totaled nearly 170,000 km², accounting for 75.1% of the study region. The emission area decreases from as much as 70,000 km² in winter and spring to around 58,000 km² in summer and autumn, accounting for 41.1 and 34.1% of the source area, respectively. During the 4 years of the study period, the emission area decreased by nearly 57 km² in winter and spring (a 0.1% change); however, the vulnerability of the land surface to wind erosion increased in ca. 190 km² and decreased in ca. 102 km². Although the area of dust emission decreased from 1996 to 2000, the area vulnerable to wind erosion increased by ca. 87 km², and the increased number of sand and dust storm days in the region between 2000 and 2003 appears to be correlated with this increase.     

近年来强沙尘暴天气气候特征的分析研究

2000～2002年春季(3～5月)中国北方有12次强沙尘暴天气过程发生,其中11次与蒙古气旋有关.作者从干旱气候背景、环流状况、沙尘源、沙尘路径及天气系统等方面进行了分析,并集中对引发强沙尘暴的蒙古气旋进行了诊断分析.结果表明:在这3年中,春季我国北方强沙尘暴天气主要与蒙古气旋的发展移动有关,气旋冷锋后的大风是强沙尘暴天气发生的主要动力因子;蒙古国南部、巴丹吉林沙漠、腾格里沙漠、乌兰布和沙漠和毛乌素沙地是强沙尘暴过程的主要沙尘源地;影响我国的强沙尘暴的沙尘路径至少可分为3种类型,即偏西路径、西北路径和南疆盆地型,以西北路径居多;我国北方春季的连续干旱、气温偏高及冷空气活跃是强沙尘暴天气形成的重要气候背景.     

A reanalysis of the Apollo light scattering observations, and implications for lunar exospheric dust

Conspicuous excess brightness, exceeding that expected from coronal and zodiacal light (CZL), was observed above the lunar horizon in the Apollo 15 coronal photographic sequence acquired immediately after orbital sunset (surface sunrise). This excess brightness systematically faded as the Command Module moved farther into shadow, eventually becoming indistinguishable from the CZL background. These observations have previously been attributed to scattering by ultrafine dust grains (radius ∼0.1 microns) in the lunar exosphere, and used to obtain coarse estimates of dust concentration at several altitudes and an order-of-magnitude estimate of ∼10⁻⁹ g cm⁻² for the column mass of dust near the terminator, collectively referred to as model “0”.We have reanalyzed the Apollo 15 orbital sunset sequence by incorporating the known sightline geometries in a Mie-scattering simulation code, and then inverting the measured intensities to retrieve exospheric dust concentration as a function of altitude and distance from the terminator. Results are presented in terms of monodisperse (single grain size) dust distributions. For a grain radius of 0.10 microns, our retrieved dust concentration near the terminator (∼0.010 cm⁻³) is in agreement with model “0” at z=10 km, as is the dust column mass (∼3–6×10⁻¹⁰ g cm⁻²), but the present results indicate generally larger dust scale heights, and much lower concentrations near 1 km (<0.08 cm⁻³ vs. a few times 0.1 cm⁻³ for model “0"). The concentration of dust at high altitudes (z>50 km) is virtually unconstrained by the measurements. The dust exosphere extends into shadow a distance somewhere between 100 and 200 km from the terminator, depending on the uncertain contribution of CZL to the total brightness. These refined estimates of the distribution and concentration of exospheric dust above the lunar sunrise terminator should place new and more rigorous constraints on exospheric dust transport models, as well as provide valuable support for upcoming missions such as the Lunar Atmosphere and Dust Environment Explorer (LADEE).     

Using X‐shooter to measure the extinction in long GRB host galaxies from emission lines

The spectra of the host galaxies of gamma‐ray bursts at low redshift generally show strong hydrogen lines of the Balmer, Paschen and Brackett series, in addition to strong nebular metal lines. In special cases the hosts can be resolved in separate star forming regions, and spatially resolved spectroscopy can be obtained. Generally, the three strongest Balmer lines are used to derive the reddening experienced by the emission lines of the host gas, assuming a Milky Way extinction curve, case B recombination and a fixed electron temperature. We demonstrate how the wide wavelength range of X‐shooter, in combination with a rigorous calibration strategy, can be used to fit explicitly for R_V, T_e, and A_V simultaneously using a large number of H and He I recombination lines, explicitly corrected for stellar atmosphere absorption. This increases our understanding of extinction and absorption in starforming regions in GRB hosts. We use two GRB hosts as examples of the methods, outlining the advantages of using X‐shooter over other instruments (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

区域气候模式对中国沙尘天气气候特征的模拟研究

现有的沙尘天气数值预报模式多选用中尺度天气模式单向耦合起沙模式的方式,不适合用来模拟沙尘气溶胶的长距离输送过程,也无法研究沙尘气溶胶辐射效应对气象场的反馈及气候变化的影响。利用一个耦合沙尘模式的高分辨率区域气候模式,模拟了2001年中国北方沙尘天气爆发的时空分布特征。模拟结果与站点观测结果对比发现,模式能够较好地模拟出中国北方主要的沙尘源地分布及沙尘天气爆发的季节变率。分析不同粒径沙尘颗粒的垂直分布特征发现,沙源地表土壤粒子特征、地形对起沙颗粒的大小都有影响;直径超过5 μm的大粒子是北方沙尘天气的主要成分,而影响长江以南的沙尘天气主要以1 μm以下的小粒子为主。对沙尘传输路径的模拟结果和实况观测发现,来自于不同沙源的沙尘天气其影响的范围有显著差异,模式能够较好地模拟出中国主要沙尘传输路径。     

2009年中国一次沙尘暴过程中的水汽变化特征及WRF回报

通过对2009年4月22日至25日发生在甘肃、宁夏、内蒙古的一次沙尘暴观测和模拟回报试验,分析了沙尘暴过程中水汽及水热的变化特征,检验了天气研究和预报模式（WRF）对沙尘暴过程的模拟能力。结果表明,WRF能较好地再现出沙尘暴过程中水汽变化的基本特征。沙尘暴发生前,地面感热明显增加,大气中水汽明显减少。在沙尘暴过程中,扩散作用和气溶胶的凝结作用影响水汽的变化,而水汽的垂直方向变化较小;高空云水和云冰含量异常偏小,低层大气的温度和水汽含量下降。热力诊断的结果表明,沙尘暴过程中,由于水汽的相变,在600～800 hPa高度处,水汽凝结产生的视热源的加热率高达6 ℃·d-1,表明非绝热加热作用在沙尘暴的维持和发展起着重要的作用。     

一次沙尘过程对天津气溶胶浓度分布的影响

利用气溶胶质量浓度和数浓度监测资料以及不同高度的常规气象资料,结合后向轨迹模式,分析2011年4月30日至5月1日一次沙尘天气过程对天津城区气溶胶浓度的影响。结果表明：沙尘过程前的轻雾天气下PM1贡献了气溶胶质量浓度的96%和数浓度的99.9%以上;本次沙尘天气存在两个不同的浮尘过程,主要区别体现在细粒子浓度差异上,第一次浮尘过程PM1~2.5、PM2.5~10和PM10~100分别占气溶胶数浓度的6.5%、2.5%和0.1%,第二次浮尘过程占比则依次为11.3%、2.6%和0.01%;两次浮尘过程气溶胶粒子性质有明显差异,第一次浮尘过程中粗粒子浓度占PM10的80%以上,第二次浮尘过程风向转变为偏北风,细粒子浓度增高至40%,气溶胶由单纯的沙尘气溶胶转变为沙尘-污染气溶胶。     

中国北部一次沙尘过程中沙尘气溶胶的时空分布及输送特性

利用CALIPSO(Cloud-Aerosol Lidar Infrared Pathfinder Satellite Observations)卫星观测资料,结合气溶胶模式模拟,分析了2011年4月28—30日发生的强度较大的一次沙尘远距离输送过程中气溶胶的时空分布特征及输送特性。结果表明,此次沙尘过程有两个源区,分别为中国南疆盆地和蒙古国中南部,并在沙尘输送过程中交汇于内蒙古西南部和甘肃地区;源区一（南疆盆地）沙尘主要分布高度在1 km以下,退偏振比平均在0.35左右,色比值平均在0.6左右,且沙尘在输送过程中被抬升到自由对流层,并先后影响内蒙古西南部、甘肃、宁夏等地区,输送到内蒙古、甘肃地区时沙尘主要分布在2.5～3 km高度,退偏振比主要分布在0.3～0.5,色比值主要分布在0.5～0.9。源区二（蒙古国中南部）沙尘先后影响内蒙古中西部地区、甘肃、山西北部、内蒙古中东部地区、河北北部、北京天津和东北地区西部部分地区,沙尘输送到中国内蒙古东部、北京、河北等地区时主要分布在1～4 km高度,退偏振比值主要集中在0.3～0.5,色比值主要在0.7～1.2。     

塔克拉玛干沙漠沙尘演变及气候因素分析

Based on the sand dust storms data and climatic data in 12 meteorological stations around sand dust storm originating areas of the Taklimakan Desert, we analyzed the trends of the number of dust storm days from 1960 to 2005 as well as their correlations with temperature, precipitation, wind speed and the number of days with mean wind speed 〉 5 m/s. The results show that the frequency of dust storm events in the Taklimakan region decreased with the elapse of time. Except Ruoqiang and Minfeng, in the other 10 meteorological stations, the frequency of dust storm events reduces, and in 4 meteorological stations of Kuqa, Korla, Kalpin and Hotan, the frequency of dust storm events distinctly decreases. The temperature has an increasing trend, while the average wind speed and the number of days with mean wind speed ≥ 5 m/s have decreasing trends. The correlation analysis between the number of days of dust storms and climatic parameters demonstrates that wind speed and the number of days with mean wind speed 〉 5 m/s have strong positive correlation with the number of days of dust storms, with the correlations coefficients being 0.743 and 0.720 （p〈0.01）, respectively, which indicates that strong wind is the direct factor resulting in sand dust storms. Whereas precipitation has significant negative correlation with the number of days of dust storms （p〈0.01）, and the prior annual precipitation has also negative correlation, which indicates that the prior precipitation restrains the occurrence of sand dust storms, but this restraining action is weaker than the same year＇s precipitation. Temperature has negative correlation with the number of dust storm days, with a correlations coefficient of -0.433 （p〈0.01）, which means that temperature change also has impacts on the occurrence of dust storm events in the Taklimakan region.