Vertical dispersion of dust particles in a turbulent boundary layer

The flow of glass dust particles in air was investigated experimentally over a flat bed in a wind tunnel. Particle concentrations were measured by light scattering diffusion (LSD) and digital image processing. It was verified that saltation is the main mechanism for ejection of dust particles. Vertical mean dust concentrations for ‘pure dust’ and two mixtures of dust and saltating glass particles were determined and analysed. The experiments confirmed that for the ‘pure dust’ configuration the mean concentration decreases as a power function with height. For the mixture configurations and for free stream velocities close to the threshold velocity, the mean concentration also decreases in a power function. For higher velocities, mean concentration decreases respectively as a power function or exponential function for large and small ratios of the dust:saltating particles respectively. The exponent of the power law reflects the dust:particle ratio and the free stream flow velocity. Copyright © 2007 John Wiley & Sons, Ltd.     

Evolution of crystal sizes in the series of dissolution and precipitation events in open magma systems

We propose a model that describes the evolution of crystal sizes and crystal size distributions (CSD) of igneous phenocrysts in a sequence of dissolution and crystallization events. This model is based on the assumption that crystal dissolution is rate-limited by diffusion in melt while crystal growth is controlled by the slower kinetic of new nucleation and growth. As a result, the dissolution rate is inversely proportional to crystal size coming into effect through the curvature of the crystal's surface, but the growth rate does not depend on the crystal size. Closed-form analytical solution of equation for CSD is obtained. We apply results of modeling to quartz and zircon, two prime minerals in silicic igneous systems that are widely used in geochemical and isotopic investigations. The time-series of multiple solution–reprecipitation episodes generate concave-downward CSDs and this result fits well with experimental and natural observations on the abundant concave-down CSD in silicic igneous rocks. We suggest that maturation of crystal populations with sizes above several micrometers can not be caused by a size effect on the solubility of the crystals (Ostwald ripening), but is rather driven by thermal oscillations in experiments and in nature. The model predicts that mean crystal size increases with time proportionally to ∼ t^0.20, which is very close to the published experimental results for quartz maturation with the exponent of 0.19–0.22. Our proposed model gives an opportunity to use natural CSDs for interpretation of pre-eruptive magma history, when solubilities and diffusion data are available for constituent elements of the dissolving mineral. In particular, we present time estimates for maturing zircon populations in large volume ignimbrites and estimate that it takes 100–1000 yrs to mature an initially exponential CSD to a lognormal CSD.     

蒙古气旋天气过程中的沙尘传输特征

基于沙尘数值预报模式针对不同区域地面起沙的敏感性试验结果,分析讨论了蒙古气旋沙尘暴过程中沙尘传输的特点及形成原因。结果表明：蒙古气旋沙尘暴过程的沙尘传输表现为:沙源区纬度越高,沙尘向东传输越强,纬度越低,向南传输越强;同时,高度越高,沙尘向东传输越强,高度越低,向南传输越强。其形成原因是萨彦岭山地背风坡效应、青藏高原东北侧地形强迫绕流等自然地理因素和蒙古气旋的动力、热力结构共同造成的,具有一定程度的普遍性。     

位涡和Q矢量诊断在毛乌素沙地沙尘天气预报中的应用

利用常规的天气图、卫星云图、湿位涡和Q矢量等,对2007年4月30日和2007年5月2日发生在毛乌素沙地的两次沙尘天气进行了综合分析\.结果表明:对流层低层MPV1＜0中尺度对流不稳定区的生成,为干对流的发生提供了不稳定能量条件;来自上游对流层中高层的干侵入和扰动干侵入在沙尘天气发生过程中起着重要作用;对流层低层由Q矢量辐散、辐合激发生成的次级环流为沙尘天气发生、发展和维持提供了动力机制。在对毛乌素沙地中β尺度沙尘暴的预报预警过程中,同时应考虑下沉对流有效位能的作用。     

Last Glacial Maximum to Early Holocene Wind Strength in the Mid-latitudes of the Southern Hemisphere from Aeolian Dust in the Tasman Sea

Dust transported by Southern Hemisphere mid-latitude westerly winds from Australia and deposited in the Tasman Sea shows no evidence for stronger winds during the last glacial maximum (LGM), compared to the Holocene. Features of the particle-size distributions of the dust do, however, indicate enhanced dry deposition of dust in the LGM changing to rainfall scavenging during deglaciation and the early Holocene as climate ameliorated. From these results it appears that activation of desert dunefields over 40% of Australia during the LGM was the result of a reduction in stabilizing vegetation and more frequent episodes of sand movement rather than of increased wind strength. The LGM climate of inland Australia must have been considerably more stressful for plants as a result of lower precipitation and/or carbon dioxide stress to achieve the implied levels of surface destabilization. Enhanced atmospheric dust loads in the Southern Hemisphere and deposition over Antarctica were most likely the result of greatly expanded source areas in the mid-latitude southern continents and a weaker hydrological cycle rather than greater entrainment or more efficient transport by stronger winds. During the LGM wind strength appears to have varied regionally, and predominantly in high latitudes, rather than uniformly for all zonal winds.     

“豫陕晋金三角”金矿成矿探讨

豫陕晋金三角是我国重要的黄金生产基地。该金三角的成矿条件极为优越,处于多构造体系复合区间,地层出露齐全、岩浆活动强烈、控金断裂系统网络交织、金源层(体)广布,所以金的成矿类型繁多,金矿床星罗棋布,文章对该区金矿成矿作专题探讨。     

含煤地层中石英组构的成因与意义——实例与实验研究

根据我国东部煤田一些实例和高温高压变形实验模拟结果表明,含煤地层中石英C-轴组构普遍具有稀疏小圆环带型式,其环带轴具有显著的应力指向意义。稀疏小圆环带型式组构的形成与石英底面滑移系的运动有关,是点极密型式的过渡状态,与石英颗粒的塑性应变量较小有关。造成含煤地层中石英颗粒塑性应变量较小的原因,除构造变形强度较小外,还与岩石中普遍存在软弱矿物有关。软弱矿物的存在吸收了大部分塑性应变      

与东秦岭超大型钼矿床有关的钾长石—石英条纹岩研究

东秦岭超大型钼矿带是世界上重要的钼矿带之一,带内分布着几个大型至超大型钼矿床。与这些大型－ 超大型钼矿床有关的岩体顶部都发育了钾长石石英条纹岩。钾长石石英条纹岩中钾长石富Ｓｉ,Ｋ,贫Ｎａ;其三斜度、有序度低。石英包裹体中Ｆ－ ,Ｋ＋高,ＣＯ／ＣＯ２ 低,缺少ＣＨ４,形成温度为４００℃～５００℃。氢氧同位素分析表明：δ１８ Ｏ＝ ９．０６×１０－ ３ ～１０．０３×１０－ ３ ,δＤ＝ － ５７．２２×１０－ ３ ～－ ７５．１０×１０－ ３ ,证明钾长石石英条纹岩的物质来自晚期岩浆热液。     

石英和碳酸钙表面位的FDIR谱学研究

本文采用漫反射红外光谱（ＦＤＩＲ）方法对石英、方解石、合成碳酸钙和孔雀石等矿物表面位（基团）作了研究。随着溶液ｐＨ值的升高,由于表面基团间氢键的影响,石英表面位〉Ｓｉ－Ｏ和〉Ｓｉ－Ｏ－Ｓｉ的吸收峰向高频方向漂移,即〉Ｓｉ－Ｏ非对称伸缩振动吸收峰由１０３６ｃｍ＾－１→１０４５ｃｍ＾－１→１０４７ｃｍ＾－１,〉Ｓｉ－Ｏ－Ｓｉ对称伸缩振动吸收峰由７７７ｃｍ＾－１→７８２ｃｍ＾－１→７８８ｃｍ＾－１,而〈     

2017年5月大气环流和天气分析

2017年5月大气环流的主要特征是极涡偏强且呈单极型分布,中高纬环流呈多波型,西太平洋副热带高压强度较常年偏强,南支槽强度较常年偏弱。5月全国平均气温17.1℃,较常年同期偏高0.9℃,为1961年以来第4高;全国平均降水量59.4 mm,比常年同期（69.5 mm）偏少14.5%,但5月7日广州出现破历史极值的极端强降水。月内我国南方地区有5次区域性暴雨天气过程;北方出现极端高温过程;东北西部、华北等地发生严重气象干旱;北方地区有2次沙尘天气过程。