戈壁近地表粉尘释放动力机制的野外风洞试验北大核心CSCD

跃移沙粒的轰击是戈壁地表粉尘释放的主要动力机制。以往对戈壁粉尘释放的包括风洞试验及野外监测的研究,由于高频测量仪器与试验方法的欠缺,无法定量化跃移沙粒能量等因素对戈壁地表粉尘释放的影响。本研究采用野外风洞,利用Sensit传感器对跃移沙粒不同能量过程进行测定,研究不同供沙条件下的戈壁近地表(0~20 cm)范围内的粉尘变化规律与地表粉尘释放动力机制。结果表明:跃移沙粒轰击作用是戈壁地表粉尘释放主要因素,也是评估粉尘释放程度的重要指征;跃移沙粒的反弹能量与粉尘释放通量相关性最强,冲击能量次之,5 cm高度撞击能量相关性最小,表明跃移沙粒轰击形成的冲击及反弹能量的转化是粉尘释放的一个重要动力过程。     

沙粒跃移云及Magnus力对床面有效粗糙度的影响

建立了考虑Magnus效应的、吹过平坦沙面的稳定风场中风与跃移沙粒相互耦合的风沙跃移云模型,并通过数值模拟研究了风沙跃移运动对床面粗糙度的影响。结果表明,跃移沙粒对风速的影响类似于床面粗糙度的影响,有效粗糙度随摩阻速度的变化关系可用二次函数表征;Magnus力对有效粗糙度有明显的影响,但这种影响并不改变有效粗糙度与摩阻风速之间的二次函数关系。     

风蚀事件中农田土壤PM10释放特征

地表风蚀导致的粉尘释放涉及全球变化研究的热点。自然条件下对粉尘释放的观测可以为风洞试验结果提供验证并为开发预测模型提供数据支撑与关键参数。本研究在河北坝上风蚀区，通过观测风蚀事件中农田近地表PM₁₀浓度、垂直通量与流失通量，以及风速和风沙流强度的变化，探讨农田风蚀过程中的粉尘释放特征。结果表明：地表风蚀释尘对近地表粉尘浓度的影响随高度增大而逐渐减弱，各高度的粉尘浓度变化趋势与摩阻风速、输沙率变化趋势相同；粉尘垂直通量和流失通量与摩阻风速呈幂函数关系，与输沙率呈线性关系；农田土壤跃移颗粒的轰击效率α数量级为10^-7m^-1。     

风沙流中跃移沙粒冲击速度和角度联合概率分布风洞实验

近地表跃移沙粒速度和角度概率分布是连接风沙运动宏观研究和微观研究的桥梁，对沙粒跃移轨迹和输沙率分布有很大影响。但是，目前跃移沙粒冲击速度概率分布和角度概率分布之间的关系还不明确。使用相位多普勒粒子分析仪（PDPA）测量了风洞沙床面1 mm高度处的跃移沙粒速度，通过分析各冲击速度对应的冲击角度的概率分布研究了沙粒冲击速度和角度的联合概率分布。结果表明：沙粒冲击速度概率分布可用对数正态函数描述，冲击角度概率分布可用指数函数描述；各冲击速度对应的冲击角度都符合指数函数分布，且其衰减速度随冲击速度增加而加快。这表明，冲击速度概率分布和冲击角度概率分布之间具有很强的相关性。最后分别给出了沙粒冲击速度和角度的独立假设概率分布和条件联合概率分布。     

基于起跳初速度分布的沙颗粒浓度廓线的数值模拟

跃移层内沙颗粒浓度分布是风沙两相流相互作用的结果,准确的沙颗粒浓度分布有助于弄清风沙互馈机制及沙颗粒间相互作用机制。由于沙颗粒浓度分布与沙颗粒起跳初速度分布以及气流运动密切相关,本文基于特定的沙颗粒起跳初速度分布函数,通过构建的沙颗粒在气流中运动的物理模型,并利用四阶精度的Adams-Bashforth-Moulton方法对所构建运动模型进行求解,统计分析稳定状态下两相流中沙颗粒运动轨迹的分布,分析其浓度廓线的垂向分布规律。计算结果表明跃移层内沙颗粒浓度分布廓线与高程呈负指数或伽马分布关系;高度一定时沙颗粒浓度廓线随摩阻风速的增大而减小,随颗粒直径的增大而增大。     

土壤风蚀中粉尘释放问题的研究进展北大核心CSCD

土壤风蚀中的粉尘释放问题是国际风沙研究的核心课题之一,近年来研究进展很快,但对研究进展的介绍还不够系统和全面。基于此,对国内外土壤风蚀中粉尘释放问题的研究历史进行了较为全面的梳理,首次进行了阶段划分,提炼了各阶段的主要研究成果,介绍了当前对粉尘释放机制的一些新认识;在对粉尘释放模型重新分类的基础上,介绍了各类模型的建模过程、优缺点及其在全球粉尘模型和区域粉尘模型中的应用。本文还提出了当前粉尘释放研究的一些热点和难点问题,希望能为相关学者开展该领域研究工作提供一定的参考。     

颗粒运动及其数理简析

根据大量的野外观测和沙(雪)颗粒运动动态摄影的资料,分析地球表面上气流带动的各种固体颗粒的主要运动形式——振动、滚动、滑移、跃移和悬移的物理图象中力的作用,给出其主要运动参数的表达式,建立各自简单的数学模型。特别对跃移运动还给出模拟轨迹方程。该模型与实际拍摄的轨迹相对比表明,较之以前风沙物理研究者模拟的跃移轨迹要好。文中首次提出的滑移概念,即振动、滚动和滑移三种颗粒运动形式代替以往分类的蠕移、跃移和悬移运动形式更准确和清晰。文中还明确回答了第一颗砂粒是怎样起跳的这一关键问题。     

稳态风沙流中沙粒体积浓度的模型分析

本文建立了一个简单有效的稳态风沙流中沙粒体积浓度的数学模型,包括3个部分:稳态风沙流的风速廓线描述、跃移沙粒轨迹的计算、床面沙粒起跳速度分布的描述。利用已知实验的风速廓线作为气流速度场输入参数,跃移沙粒轨迹的计算主要考虑重力和拖曳力,基于体积观点的床面起跳沙粒的水平速度和垂直速度概率密度分布函数分别采用正态分布和指数分布函数来描述。根据稳态风沙流中运动沙粒的动态平衡特征可推导计算沙粒体积浓度。计算的沙粒体积浓度与风洞实验结果基本一致,说明本模型有较好的预测能力。     

风沙环境中公路风沙灾害的数值模拟

为揭示沙漠公路两侧风沙流场的空间分布特性，采用欧拉-拉格朗日方法，把气流作为连续介质，把沙粒作为离散体系，利用ANSYS标准k-ε湍流模型和DPM离散相模型，模拟了不同沙粒粒径（150、200、250、300、350 μm）、不同摩阻风速（0.20、0.35、0.50、0.65、0.80 m·s^-1）、不同挡风墙高度（1.0、1.5、2.0、2.5、3.0 m）以及不同挡风墙开孔情况下的公路路基附近的沙粒跃移运动，统计了挡风墙前后的沙粒数目，给出了公路路基坡脚和坡顶等典型断面上的气流速度廓线。结果表明：气流通过挡风墙顶部时受压加速，有利于沙粒的输送，而在挡风墙前部气流遇阻减速，形成沙粒堆积。随着沙粒粒径的变大，沙粒跃过挡风墙的能力逐渐变低；随着摩阻风速的变大，气流输运能力增强，更多沙粒越过挡风墙；随着挡风墙高度的增加，阻挡沙粒数亦逐渐增多；挡风墙开孔的位置和大小亦影响着沙粒的运动。这表明离散相模型对复杂下垫面风沙跃移运动的计算具有良好的效果。     

农牧交错带农田土壤风蚀PM10释放特征

粉尘释放是风蚀造成危害的一个重要过程。以农牧交错带沙区和非沙区农田土壤为研究对象,利用室内风洞模拟实验,实时监测了风蚀过程中释放的PM₁₀,分析了PM₁₀的动态变化特征,以深入认识土壤风蚀粉尘释放机理。结果表明：非沙区农田土壤风蚀强度远低于沙区农田,与风速呈指数函数关系;非沙区农田的土壤粉尘释放在不同风速下均以气流直接抬升模式为主,平均PM₁₀通量与风速呈线性函数关系,最大PM₁₀通量与风速呈幂函数关系;沙区农田的土壤粉尘释放在风速增大到一定程度后呈气流直接抬升和砂粒跃移冲击复合模式,最大PM₁₀通量增加不明显,但平均PM₁₀通量明显高于非沙区农田;对于沙区和非沙区农田而言,平均PM₁₀通量与风蚀速率呈对数函数关系。     

Theoretical expressions for soil particle detachment rate due to saltation bombardment in wind erosion

Saltation bombardment is a dominate dust emission mechanism in wind erosion. For loose surfaces, splash entrainment has been well understood theoretically. However, the mass loss predictions of cohesive soils are generally empirical in most wind erosion models. In this study, the soil particle detachment of a bare, smooth, dry, and uncrusted soil surface caused by saltation bombardment is modeled by means of classical mechanics. It is shown that detachment rate can be analytically expressed in terms of the kinetic energy or mass flux of saltating grains and several common mechanical parameters of soils, including Poisson's ratio, Young's modulus, cohesion and friction angle. The novel expressions can describe dust emission rate from cohesive surfaces and are helpful to quantify the anti-erodibility of soil. It is proposed that the mechanical properties of soils should be appropriately included in physically-based wind erosion models.     

风蚀影响因子的敏感性试验

 对风蚀模式的各重要影响因子进行了敏感性试验，结果表明：①随风力的增大，跃动沙粒的粒径范围迅速增大，从而会使更多、更大的尘粒因受到更强烈的撞击作用而释放于空中。但随土壤水分和植被覆盖度的增加，跃动沙粒粒径范围会变窄，较大的粒子很难被激发到空中。②各种土壤沙流通量及尘粒释放率随粒径的变化趋势Q(d)和F(d)与相应的地表土壤有效粒度分布Ps(d)具有相似的特征，说明前人用近地层沙尘粒度分布来代表地表土壤的有效粒度分布是合理的。③若以总沙流通量Q>0.5 g·m^-1·s^-1为风蚀过程开始发生的标准，在干燥、裸露的情况下，沙土、沙壤土、壤土、黏土和粉黏土表面发生风蚀的临界摩擦速度都约为0.3 m·s^-1。相同风力条件下（u*=0.6 m·s^-1），若地表干燥（w=0）并忽略小于0.1 g·m^-1·s^-1的总沙流通量，则抑制5种土壤发生风蚀的最小植被覆盖度分别约为：沙土0.35、沙壤土0.45、壤土0.45、黏土0.55、粉黏土0.55；若地表裸露，抑制风蚀发生的最小水分含量分别为：沙土0.15、沙壤土0.18、壤土0.3、黏土0.36和粉黏土0.33。④通常情况下沙土最不易起尘，它在各个粒径的尘粒释放率比其他土壤均约小3~5个量级。粉黏土最易起尘，且粒径较小，较容易传输到下游很远处。⑤总尘粒释放率F和总沙流通量Q随风力、地表条件的变化一般是同相的，即Q增大，F也会增大。⑥一般情况下F随摩擦速度u*的增大或植被覆盖度cf和土壤水分w的减小而增大；土壤拖曳系数sx和弹性压力垂直分量pye的增加会大大降低尘粒释放率。⑦通常风蚀情况下，5种土壤中粉黏土和沙壤土因聚合粒子破碎产生的尘粒释放率Fc最大，Fc随风力、地表条件变化的敏感度也最强；沙土的Fc最小，其对风力、地表条件的敏感度也最弱。     

塔克拉玛干沙漠塔中地区春夏季风蚀起沙研究

利用塔克拉玛干沙漠腹地塔中地区的观测资料,对塔中地区春夏季地表土壤风蚀起沙的临界摩擦速度及其变化特征和起沙风速进行了分析研究,并计算了2008年4月19日和7月19日两次沙尘暴天气过程沙漠地表的风蚀起沙量。结果表明:塔中地区春夏季地表起沙的临界摩擦速度为0.26 m·s-1;2 m高度的临界起沙风速约为4.1 m·s-1;两次沙尘暴过程的顺风向沙粒通量和垂直尘粒通量的平均值分别为17.44×10-4 kg·m-1·s-1 、13.8×10-8 kg·m-2·s-1、164.69×10-4 kg·m-1·s-1和799.77×10-8 kg·m-2·s-1;沙尘通量的变化与风速及摩擦速度的变化具有一致性。     

Influence of soil texture on the binding energies of fine mineral dust particles potentially released by wind erosion

Models of the two aeolian processes (saltation and sandblasting) that lead to emission of fine dust particles (PM20) by wind erosion in arid and semi-arid areas have been combined to form the so-called ‘Dust Production Model’ (DPM). In this model, the size dependent binding energies of PM20 embedded within the wind-erodible loose soil aggregates or in the soil surface itself are key input parameters. Indeed, their values condition at the same time the intensity of emissions and their initial size distribution. Previous comparisons of vertical mass fluxes measured on-field with the model predictions suggest that these energies might be relatively independent of soil texture and also probably composition. Because this would greatly facilitate application of the DPM at regional or global scale, the objective of this work is to check experimentally the veracity of this result. The strategy that has been designed for this has involved selecting four natural soil samples collected in various source areas of the world and covering a wide range of textures and compositions. Then, these soil samples have been used to perform carefully controlled wind erosion simulations in a wind tunnel. During the experiments, which were carried out at different wind speeds with each soil, the horizontal flux (F_h) of saltating soil aggregates has been monitored. At the same time, number concentrations (C_i) of PM20 released by the sandblasting process were recorded in the 6 size classes of an optical size analyzer. Thus, the efficiency of the sandblasting process (defined as the ratio of C_i to F_h) could be determined for each of these size classes. Analysis of the results obtained in similar saltation conditions shows that for the four tested soils, and within the range of contents in clay and other components favoring aggregation (mostly organic matter and carbonates), the influence of soil composition and texture on binding energies of the PM20 particles within soil aggregates is at best a second order effect that can be neglected in large scale modeling of wind erosion by the DPM.     

内蒙古拐子湖地区风沙运动若干参数计算

 利用内蒙古拐子湖地区风沙观测场2011年3～5月的沙尘暴强化观测资料,分析计算了巴丹吉林沙漠北缘平坦沙地的地表粗糙度、临界摩擦速度、临界起沙风速等风沙运动关键参数。初步结论如下：观测期间地表粗糙度的变化范围为1.0×10-7～ 9.0×10-1cm,平均粗糙度为0.942 cm;临界摩擦速度约为0.34 m/s;2 m高度的起沙风速约为4.6 m/s。     

利用遥感综合分析西风引导气流与地形对沙尘运移路径的影响

沙尘暴的发生受大气环流、地表状况、降雨的影响，还受到局部地区地形的影响。一次规模较大的沙尘暴过程，沙尘可以从蒙古国和我国西部沙源地输送到我国东部、韩国、日本乃至夏威夷、美国西海岸。中日亚洲沙尘暴ADEC项目对亚洲沙尘暴的起沙、传输和降落的运行机制已经作了深入的研究，并建立了亚洲沙尘暴的数值模拟系统。本文以影响北京地区的沙尘暴事件为例，利用遥感技术，综合DEM地形数据和地面实测数据分析西风引导气流和地形对沙尘运移路径影响，将MODIs影像数据和DEM地形数据以及地面观测站点实测数据相结合，进行综合分析，结果表明在一次沙尘暴过程中，沙尘在运移过程中的运移路径明显地受到西风引导气流、沙尘粒子自然沉降规律以及局部地形的影响，要预防(减少)北京地区的沙尘暴仅仅作好北京地区的生态环境建设是不够的，加强北京周边地区，尤其是张家口地区、官厅水库库区及库区周围地区的生态环境建设尤为重要。     

艾比湖干涸湖底不同地表类型风蚀强度及粉尘输移通量的风洞试验研究

以新疆准格尔盆地西部艾比湖干涸湖底及相关邻近地区7种不同形态的原状土为研究对象,通过风洞模拟试验,揭示干涸湖底不同地表类型的风蚀强度和沙/盐尘低空输送通量。结果表明：粉状盐漠和含盐量较低的淤泥-粘土混合物临界启动风速最低,硬质盐壳的临界启动风速最大;大于16 m·s-1的大风是造成艾比湖干涸湖底风蚀的主要动力,7种地表类型中湖相沉积物、风积物、粉状盐漠的风蚀率最大,是风蚀尘暴的主要尘源;风蚀过程中颗粒的初始运动主要集中在0~10 cm高度范围内,以近地面跃移为主,风积物、湖相沉积物和粉状盐漠的输移通量最大。     

Estimation of PM20 emissions by wind erosion: main sources of uncertainties

The physics of the two processes (saltation and sandblasting) leading to fine mineral dust emissions by wind erosion in arid or semi-arid areas has been detailed and modeled. The combination of these two models has led to a physically explicit Dust Production Model (DPM). In this work, sensitivity tests are performed with the DPM to determine the nature of the main soil parameters that control dust emissions by sandblasting. It is found that the soil roughness length and the dry size distribution of the soil aggregates constituting the loose wind erodible fraction of the topsoil have the greatest influence on the soil potential for mineral dust production. Contrary to what is often assumed, soil texture is not a relevant parameter.In the light of these new findings, results of vertical flux measurements performed over a wide variety of sources in Niger and the US south west (14 soils) have been reanalyzed. Results show (1) that for the tested soils the DPM, and hence sandblasting, explain all dust emissions, and (2) that 13 of the 14 soils that had been selected a priori for their high potential for dust emissions contained a fine soil-aggregate component. This is consistent with the sensitivity tests indicating that the presence of such a component could enhance dust emissions by one order of magnitude. Finally, it can be concluded that most of the apparent scatter in the experimental results was in large part due to an inappropriate choice of soil parameters to interpret them.     

Eolian Dust Erosion from an Agricultural Field on the North Carolina Coastal Plain

Eolian erosion typically has not been considered a significant process on the humid southeastern coastal plain of the United States. A preliminary study of eolian erosion from an agricultural field was undertaken during the late winter of 2002 and early spring of 1999. During those times local agricultural practices leave fields bare while frontal systems produce frequent high wind events. Dust emissions were measured with two samplers; modified Wilson and Cooke passive dust traps and high-volume air samplers. Results of the study indicate that wind erosion is a significant process on agricultural fields of the North Carolina Coastal plain. Dust flux off of the field during the largest of five measured events was estimated as high as 126 kg/m with total losses of 3070 kg/ha. Atmospheric concentrations of suspended material were measured at 58,815 μgm^-3. Sediment erosion was not evenly distributed across the field. Erosion was focused over soils that are better drained. Low levels of soil moisture did not eliminate erosion but instead produced pulses of sediment emission as sustained wind continually dried then activated sequential layers of the field surface. Soil moisture and topography appear to be the primary controls on spatial erosion differences and soil characteristics likely play a secondary role.