Simulation of Terrestrial Dust Devil Patterns

Introducing the surface properties [initial vortex, ground temperature and surface momentum impact height (SMIH)] for the boundary conditions, dust-devil-scale large eddy simulations (LES) were carried out. Given three parameters of initial vortex, ground temperature and the SMIH based on Sinclair's observation, the dust devil physical characteristics, such as maximum tangential velocity, updraft velocity, pressure drop in the inner core region, and even reverse flow at the top of the core region, are predicted, and are found to be close to the observations, thus demonstrating the ability of the simulation. The physical characteristics of different modeled dust devils are reproduced and compared to the values predicted by Renno et al.' theory. Even for smaller temperature differences or weaker buoyancy, severe dust devils may be formed by strong incipient vortices. It is also indicated that SMIH substantially affects the near-surface shape of terrestrial dust devils.     

中、美和苏丹强沙尘暴的对比分析

为了更好地认识我国的强沙尘暴，对中、美和苏丹三地的强沙尘暴个例进行了对比分析，讨论了它们之间的异同，强调了我国西北的强沙尘暴也存在干飑线对流特征和雷暴下曳气流的作用     

东亚春季沙尘天气的卫星云图特征分析和分型

2001年春季,沙尘天气对我国北方地区产生了较大的影响,作者给出了卫星遥感监测到的沙尘过程的图像特征并对产生沙尘的天气系统进行了云图分型.最后得出沙尘天气主要发生在3种天气系统及相应的云系分布类型下.     

塔克拉玛干沙漠腹地贴地层风沙流结构研究

利用微梯度集沙仪在塔克拉玛干沙漠腹地塔中地区实测的2014年7—8月贴地层输沙量梯度观测资料(观测高度区间0~5 mm、5~15 mm、15~35 mm、35~85 mm),对沙尘天气过程贴地层风沙流结构进行了研究。结果表明:(1)沙尘天气(沙尘暴和扬沙)过程中,随着风速的增大,各高度层输沙量也随之增大。沙尘暴天气中,风速7.5 m·s~(-1)时,15~35 mm处的百分含量超过5~15 mm处的百分含量,风速7.5 m·s~(-1)时,15~35 mm处的百分含量达到最大,其余各高度含量变化不明显。扬沙天气中,风速8.0 m·s~(-1)时,百分含量最大值出现在35~85 mm高度处,占48.9%,风速8.0 m·s~(-1)时,大小依次为:15~35 mm(49.5%)35~85 mm(31.7%)0~5 mm(12.7%)5~15 mm(9.2%)。(2)两种天气过程中,沙粒的平均粒径在垂直高度上均呈现先减小后增大的趋势。粒径峰值均处在125~250 um,极细砂含量最高,细砂次之。与扬沙天气相比,沙尘暴天气过程中极细砂、细砂、中砂在各高度层上的含量略微下降,粉尘含量有所升高。     

沙尘暴研究中的若干科学问题

近年来,中国北方频繁发生的沙尘暴事件引起世人的关注.实际上,沙尘暴不仅影响空气质量、交通,造成土壤风蚀和其他人、畜生命财产等社会、经济损失,作为一种特殊类型的大气气溶胶,沙尘粒子还具有重要的气候和环境效应.作者在简单综述沙尘暴研究的基础上,将重点探讨沙尘暴研究中一些值得注意的科学问题.     

基于CALIPSO资料的沙尘暴过程沙尘垂直结构特征分析

综合利用CALIPSO星载激光雷达探测资料和MM5数值模拟结果,对2010年3月19—22日强沙尘暴过程不同阶段沙尘垂直分布特征及其动力、热力结构进行了初步分析,结果发现:在沙尘暴成熟阶段,沙尘层分布于2~9 km(850~250 hPa)的几乎整个对流层中,冷锋前抬升和锋后下沉导致的旺盛垂直混合使沙尘呈现相对均匀的垂直分布。在沙尘扩展及远距离传输阶段,沙尘层明显分为两层,分别位于对流层低层(700 hPa以下)和对流层中高层(600~300 hPa)。在沙尘暴各个阶段,弱风速垂直切变和弱位温、相当位温垂直变化始终与沙尘层配合,显示沙尘层维持中性混合层,而两个沙尘层之间则为强风速垂直切变及位温、相当位温锋区。另外,沙尘暴发展过程中,高空急流、位涡、比湿等要素均表明出明显的对流顶折叠和高空位涡下传,且在对流顶较高的区域,沙尘向上的扩展也较高,反之则较低。需要指出,在沙尘暴扩展和远距离传输阶段,在40°N附近,7~9 km沿纬向一线,均出现一小范围孤立沙尘区位于平流层中(或平流层附近),表明沙尘暴过程中能够产生沙尘的对流层—平流层输送,并在平流层中形成持续性的沙尘传输带。这可以成为沙尘气溶胶对流层—平流层输送及其在平流层中传输的一个直接的监测证据。     

The Umov effect for single irregularly shaped particles with sizes comparable with wavelength

The Umov effect manifests itself as an inverse correlation between the linear polarization maximum of an object’s scattered light P_max and its geometric albedo A. This effect is observed for the Moon, Mercury and Mars, and there are data suggesting this effect is valid for asteroids. The Umov effect is due to the contribution of interparticle multiple scattering that increases albedo and decreases polarization. We here study if the Umov effect can be extended to the case of single irregularly shaped particles with sizes comparable with the wavelength. This, in particular, is important for cometary dust polarimetry. We show the Umov effect being valid for weakly absorbing irregular particles (Im(m) ? 0.02) almost through the entire range of size parameters x considered. Highly absorbing particles (Im(m) > 0.02) follow the Umov effect only if x exceeds 14. In the case of weakly absorbing particles, the inverse correlation is essentially non-linear, which is caused by the contribution of particles with small x. However, averaging over many different types of irregularly shaped particles could make it significantly more linear. The size averaging does not change qualitatively the diagram log(P_max)-log(A) for weakly absorbing particles. For single irregular particles whose sizes are comparable with wavelength, there is no reliable correlation between the slope of the polarization curve h near the inversion phase angle and geometric albedo A. Using the extended Umov Law, we estimate the geometric albedo of dust particles forming cometary circumnuclear haloes A = 0.1 − 0.2, which is a few times larger than the average geometric albedo over the entire comae. Note that, using the obtained values for A of cometary particles, one can derive their number density in circumnuclear haloes from photometric observations.     

河西走廊干旱区春季沙尘气溶胶对辐射的影响初步研究

利用2008年春季中美沙尘暴联合观测实验中张掖站晴朗少云天正午的地表辐射和太阳光度计资料,计算分析了沙尘气溶胶对太阳辐射和大气逆辐射的影响,结果表明：沙尘对太阳总辐射有一定程度的削弱作用,经估算,大气浑浊度每增加0.1,太阳总辐射平均减少约10.45 W·m^-2;当大气浑浊度一定时,沙尘粒子越小,对太阳总辐射的削弱效率就越高;大气浑浊度小于0.3时,大气逆辐射有随大气浑浊度的增加而增加的趋势,大气浑浊度大于0.3时,大气逆辐射随大气浑浊度增加有减小的趋势。     

Intercomparison of PIXE and ICP‐AES Analyses of Aeolian Dust from Owens (Dry) Lake,California

Particle‐induced X‐ray emission (PIXE) and ICP‐AES can be combined to obtain a wider range of detected elements, augment previous data and/or to verify measured concentrations of heavy and trace metals in geological samples. Intercomparison of data sets generated by multiple techniques is challenging due to the differing processes and methods of each technique. Here, we compare elemental data obtained by both techniques for aeolian dust from Owens (Dry) Lake, California. Nineteen elements were detected by PIXE, sixteen by ICP‐AES and ten elements were detected by both techniques. Statistical analyses of data set groupings illustrated which parameters differed significantly between PIXE and ICP‐AES. Relative variation (%) showed that PIXE gave higher concentrations than ICP‐AES for Al, As, Cu, Fe, K, Mn, Ni, Sr, Ti and Zn in all samples. For As, Cu, Sr and Zn, relative variation was variable between the techniques. PIXE detection limits exceeded ICP‐AES concentrations for Ba, Cd, Co, Cr, Pb and Mo. Low ICP‐AES percentage recoveries of Al, Fe, K, Mn and Ti for NIST SRM 2710 indicated incomplete dissolution during digestion (EPA Method 3050B), since elements were bound in silicate structures. Variability between the two data sets is explained by differences between analytical techniques, sample preparation methods and/or variability in sample matrices.