CLOUDS AND PRECIPITATION IN THE TEXAS HIGH PLAINS1

A study of the relationship among cloudiness, precipitable water vapor, stability and precipitation is presented for the Texas High Plains. A study of clouds during periods of above-normal rainfall indicates that precipitation during late fall and winter is associated with stratiform clouds which develop in conjunction with cyclonic activity. Spring and summer precipitation is most highly correlated with cumuliform clouds characteristic of convective activity. Investigation of other macroscale atmospheric features indicates that wet periods are further characterized by atmospheric instability and above-normal amounts of precipitable water vapor and water-vapor flux. Dry periods are associated with atmospheric circulation patterns which either serve to cut off the supply of low-level moisture, produce subsidence and consequent atmospheric stability, or both.     

层状云降水中化学过程的数值模拟

对一维时变的层状云物理化学模式的化学过程作了研究,引入了较为细致的化学模式,并以类似化学反应方程式的方式处理了气液传输、碰并和云雨转化过程。在此基础上讨论了典型条件下的云雨酸化过程。模拟结果表明,高空云雨水组成随时间逐渐减小,地面雨水组成呈峰型分布。在降水后期pH值主要同O₃和SO₂有关;主要来自气溶胶,来自NH₃,气体和气溶胶对的贡献大致相当,和Ca￣(2＋)的云下清除约占60％～80％;在降水前期H₂O₂时S(Ⅳ)的氧化超过O₃,降水后期S(Ⅳ)的氧化主要通过O₃。      

武山铜矿层状含铜黄铁矿矿体锶同位素地球化学特征及矿床成因

武山铜矿层状含铜黄铁矿矿体与花岗闪长斑岩具有完全不同的Sr同位素组成。层状矿体中胶黄铁矿、黄铁矿的87Sr／86Sr比值变化于0．7117－0．7241之间，而花岗闪长斑岩中长石和磷灰石的87Sr／87Sr在0．7072-0．7099之间。表明二者具有不同的物质来源，层状矿体物质主要来自上地壳和地层。而花岗间长班岩则主要来自上地幔和下地壳。铅同位素组成表明层状矿体中的铅来自古生代地层。层状矿体硫化物的Rb－Sr等时线年龄为328±21Ma，87Sr／86Sr的初始值为0．7138，表明民状矿体矿石形成于石炭纪，成矿物质自上地壳；而花岗闪长班岩的Rb－Sr等时线年龄为140Ma，为燕山早期的产物。根据研究结果，并结合矿体地质特征等，我们认为武山层状含铜黄铁矿矿体为与海西期海底火山活动有关的喷气（热水）沉积矿床。     

Measurement of minimum ignition energies (MIEs) of dust clouds – History,present, future

Nearly 130 years ago Holtzwart and von Meyer (1891) demonstrated by experiments that explosible dust clouds could be ignited by inductive electric sparks. Then more than half a century passed before the publication of the important quantitative research of Boyle and Llewellyn (1950) and Line et al. (1959). They worked with capacitive electric sparks and found that the minimum capacitor energies ½CU² required for ignition of various dust clouds in air decreased substantially when a large series resistance, in the range 10⁴–10⁷ Ω, was introduced in the discharge circuit. When considering that the net energies of the sparks themselves were only of the order of 10% of the ½CU² discharged, the minimum net spark energies required for ignition with a large series resistance were only a few per cent of the net energies required without such a resistance.Line et al. observed that the essential effect of increasing the series resistance, and hence increasing the discharge time of the sparks, was to reduce the disturbance of the dust cloud by the blast wave from the spark. This phenomenon was explored further by Eckhoff (1970, 2017), and subsequently by some simple experiments by Eckhoff and Enstad (1976). Franke (1974, 1977) and Laar (1980) confirmed the additional finding of Line et al. (1959) that the minimum ½CU² for ignition is also substantially reduced by including a series inductance in the discharge circuit, rather than a series resistance. The basic reason is the same as with a large series resistance, viz. increased spark discharge time and hence decreased disturbance of the dust cloud by blast wave from the spark. For this reason inclusion of an appreciable series inductance in the spark discharge circuit is an essential element in current standard MIE test methods.In experiments with spark ignition of transient dust clouds produced by a blast of air in a closed vessel, it is necessary to synchronize the occurrence of the spark with the formation of the dust cloud. The precision required from this type of synchronization is typically of the order of 10 ms, which can be obtained even by mechanical arrangements, such as rapid change of spark gap length, or of the distance between two capacitor plates. The present paper reviews some methods that have been/are being used for achieving adequate synchronization of dust cloud appearance and spark discharge. Some current standard experimental methods for determining MIEs of dust clouds experimentally have also been reviewed. The same applies to some theories of electric-spark ignition of dust clouds.At the end of paper some suggestions for possible future modifications of current standard methods for measuring MIEs of explosible dust clouds are presented. With regard to justifying significant modifications of existing standard methods, the “bottom line” is, as quite often in many connections, that any modifications should be based on realistic cost/benefit evaluations.     

Testing of dust clouds for the electrostatic-spark ignition hazard in industry. Need for a modified approach?

Current standard test methods for electric-spark minimum ignition energies (MIEs) of dust clouds in air require that a series inductance of at least 1–2 mH be included in the electric-spark discharge circuit. The reason is to prolong the spark discharge duration and thus minimize the spark energy required for ignition. However, when assessing the minimum electrostatic energy ½CU² for dust cloud ignition by accidental electrostatic-spark discharges, current testing standards require that the series inductance of at least 1–2 mH be removed from the spark discharge circuit. No other changes of apparatus and test procedure are required. The present paper questions whether this simple approach is always adequate. The reason is that in practice in industry accidental electrostatic-spark discharge circuits may contain large ohmic resistances due to corrosion, poor electrical grounding connections, poorly electrically conducting construction materials etc. The result is increased spark discharge durations and reduced mechanical disturbance of the dust cloud by the blast wave emitted by the spark. Therefore, testing for minimum ½CU² for ignition by accidental electrostatic spark discharges may not only require removal of the series inductance of 1–2 mH from the standard MIE spark discharge circuit. Additional tests may be needed with one or more quite large series resistances R_s inserted into the spark discharge circuit. The present paper proposes a modified standard test procedure for measurement of the minimum electrostatic-spark ignition energy of dust clouds that accounts for these effects.     

冰核对华北平原地区积云发展的影响

利用包括双参数化微物理方案的云分辨的WRF模式（简称CR-WRF）,对2014年8月24日发生在华北平原地区的一次积云过程进行了数值模拟。CR-WRF模式比较全面地考虑了气溶胶粒子的活化过程,对不同气溶胶的不同核化方案进行了参数化,包括云凝结核（CCN）的核化、冰核（IN）的均质和异质核化等,令其浓度分为HCCN,MCCN和LCCN三个等级,分别对应数密度为 9000 cm^?3,900 cm^?3和90 cm^?3的情况下,考虑黑碳气溶胶（BC）作为IN,将其数浓度从2 cm^?3增加至 2000 cm^?3,并且在CCN浓度不变的情况下,通过改变BC的浓度探讨积云微物理过程对IN的响应。模拟结果表明：在LCCN条件下,BC浓度很低的时候冰晶数浓度大于HCCN情况下的冰晶浓度。随着BC浓度的不断增加,冰晶粒子数浓度在HCCN条件下迅速增长,并超过了LCCN和MCCN情况下的冰晶数浓度。这是由于LCCN条件下,BC浓度较低时云内过饱和水汽含量高于HCCN情况下的含量,从而形成了较多的冰晶粒子;而随着BC浓度的不断增加,在HCCN条件下的上升气流逐渐大于LCCN条件下的上升气流,因此在HCCN条件下的冰晶得以迅速增长。随着BC浓度的增长,云滴数浓度没有明显的变化;而云滴有效半径呈现出随BC浓度的增长而减小的趋势。这是由于BC对云滴粒子的形成没有较大贡献,随着BC的增加云内上升气流增强,导致云滴粒子有效半径减小。此外,对流中心上升速度随BC浓度的增长而增长;与此同时,下沉速度在LCCN情况下随BC浓度的增长而增长,在HCCN和MCCN情况下则随BC浓度的增长而减小。由此得出以下结论：在LCCN条件下由于云滴粒子的核化过程较低,因此对冰晶的异质核化过程提供了足够的水汽,使得在BC浓度很低的情况下冰晶数浓度大于HCCN和MCCN的条件。由于相变过程会不断地释放潜热,使云内对流中心上升气流增大,下沉气流减弱,并产生更多粒径较小的云滴粒子,从而起到抑制降水发生的作用。     

多无人机协作监测污染气团的研究现状

分析了多无人机协作监测污染气团的研究意义,以及涉及到的4个主要技术问题——未知环境的搜索方法、环境地图建模、任务分配和路径规划的研究现状,指出多无人机协作监测研究的仿真平台、三维空间的监测技术及精确的模型是开展该项工作的重要研究方向。     

青海湖沙柳河河源区降水同位素云下二次蒸发效应

河源地区的水源储蓄和涵养能力,深刻影响河流的水资源补给与供续,研究河源地区降水同位素的二次蒸发效应有助于深入理解河源区降水循环过程。选取2020年5～9月青海湖沙柳河河源地区的逐月降水同位素数据,利用基于稳定同位素的Stewart雨滴蒸发模型,计算了青海湖沙柳河河源地区雨滴蒸发剩余比(f),以及蒸发分馏的氢氧同位素组分(Δδ¹⁸O、ΔδD和Δd),探讨了研究期内Δδ¹⁸O、ΔδD、Δd和f的差异以及影响因素,结果表明：(1)青海湖沙柳河河源区5～9月地面降水同位素δD_p、δ¹⁸O_p和d-excess_p平均值分别为-30.93‰、-6.67‰和22.42‰;云下降水同位素δD_c、δ¹⁸O_c和d-excess_c平均值分别为-49.57‰、-11.16‰和39.70‰。云下二次蒸发效应使降水d-excess值发生贫化。(2)沙柳河河源区5～7月f和Δd均值分别呈上升趋势,7～...     

On East Asian Sand and Duststorms and Associated Significant Dustfall Observed from January to May 2001

Monitoring of dust pollution at the western shore of Tae-ahn Peninsula (TAP) and in the Chongju area of central Korea was carried out from January to May 2001. It was found that in Koreathere were 9 cases of sand and duststorms (DS) and 16 associatedsignificant dustfall (SD) days. Observed maximum concentrations of DS and SD coming from NW China and Mongolia were in the rangeof 300–920 for TSP, 200–690 for PM₁₀ and 100–170 g m^-3 for PM_2.5.Satellite measurements clearly showed the formation and subsequent movement of DS to the Korean Peninsula and onward to the Korea East Sea, Japan and the Gulf of Alaska. According to satellite image analysis of dust clouds there were abundant coarse particles, measuring in size of 11.0 m. Medium-sizedparticles measuring in the range of 3.5–7.0 were also prevalent,while fine particles of less than 2.0 m were less distinctive in reflectivity. Measured values of PM_2.5 were alsorelatively low with SD events.The measured average pH values of dusty precipitation associatedwith DS were 7.24. Alkaline precipitation can play a `temporary'role in the neutralization of acidified soil until the subsequentevent of acidic rain. The new selection criteria of SD days from PM_2.5 at 85 g m^-3, PM₁₀ 190 g m^-3 and TSP 250 g m^-3 are recommended on dust pollution occurring from the invasion of a DS elsewhere.     

A theoretical model for the prediction of the minimum ignition energy of dust clouds

In this study, a physical model of the dust cloud ignition process is developed for both cylindrical coordinates with a straight-line shaped ignition source and spherical coordinates with a point shaped ignition source. Using this model, a numerical algorithm for the calculation of the minimum ignition energy (MIE) is established and validated. This algorithm can evaluate MIEs of dusts and their mixtures with different dust concentrations and particle sizes. Although the average calculated cylindrical MIE (MIE_cylindrical) of the studied dusts only amounts to 63.9% of the average experimental MIE value due to reasons including high idealization of the numerical model and possible energy losses in the experimental tests, the algorithm with cylindrical coordinates correctly predicts the experimental MIE variation trends against particle diameter and dust concentration. There is a power function relationship between the MIE and particle diameter of the type MIE ∝ d_p^k with k being approximately 2 for cylindrical coordinates and 3 for spherical coordinates. Moreover, as dust concentration increases MIE(conc) first drops because of the decreasing average distance between particles and, at fuel-lean concentrations the increasing dust cloud combustion heat; however, after the dust concentration rises beyond a certain value, MIE(conc) starts to increase as a result of the increasingly significant heat sink effect from the particles and, at fuel-rich concentrations the no longer increasing dust cloud combustion heat.