【作者】 牛生杰；

【导师】 孙照渤；

【作者基本信息】 南京气象学院 ， 大气科学， 2004， 博士

【摘要】 深入滕格里沙漠、巴丹吉林沙漠、毛乌素沙地等沙漠源地采用直接测量的方法对沙尘天气进行了综合观测。观测项目包括：微气象学测量、三维风速测量、KB-120和Anderson采样、APS—3310A粒子谱仪以及太阳光度计观测，并用中子活化方法分析了沙尘气溶胶的元素浓度。利用所取资料，系统分析了不同强度沙尘天气条件下沙尘气溶胶质量浓度和质量浓度谱、粒子谱分布、光学厚度、化学组分等特征；综合分析了影响沙尘起动的诸物理因子在沙尘起动中的作用；用沙尘输送模式对一次沙尘暴天气造成的泥雨过程的形成机制进行了模拟。 历史气象资料统计分析表明，沙尘暴有其高发期（4、5月）和高发时段（14-20时），14时到20时之间发生的沙尘暴约占沙尘暴总次数的66％。 扬沙和沙尘暴天气条件下，湍流动量通量和湍流感热通量都是重要的湍流交换，沙尘暴发生前近地层的超绝热不稳定对沙尘暴天气有加强作用。沙尘天气条件下σ_y和σ_z的日变化特征与沙尘天气起始时间有关。 银川、巴音浩特和通古淖尔三地背景大气沙尘气溶胶粒子的数浓度谱和质量浓度谱均呈单峰型，服从对数正态分布，与城市污染物气溶胶的三峰、双峰质量谱明显不同。浮尘、扬沙、沙尘暴天气条件下，平均数浓度和质量浓度是依次增加的，可相差4-7倍。沙尘气溶胶粒子谱分布还与地理位置有关。 背景大气、浮尘、扬沙、沙尘暴天气平均质量浓度依次存在倍数关系。从沙尘气溶胶TSP平均质量浓度来看，背景大气（82.8μg／m³）、浮尘天气（356.4μg／m³）、扬沙天气（1205.8μg／m³）、沙尘暴天气（3955.3μg／m³），从中可以看出，浮尘天气TSP是背景大气的4.30倍，扬沙天气TSP是浮尘天气的3.38倍，沙尘暴TSP天气是扬沙天气的3.28倍。 沙尘天气下以亲地壳元素为主的气溶胶元素浓度均高于背景大气和浮尘天气，而且沙尘天气强度愈强，元素浓度的增加愈显著；背景大气、浮尘天气条件下亲地壳元素的浓度一般在10^-1～10⁰μg／m³量级，扬沙、沙尘暴时一般达10¹μg／m³量级，特强沙尘暴时高达10²μg／m³量级。 在沙尘气溶胶中，亲硫元素和亲沉积层元素的富集程度均较高，元素的易挥发性常使其富集程度明显提高，污染元素易在细颗粒上富集。摘要 在浮尘、扬沙和沙尘暴天气下，大气气溶胶光学厚度迅速增大，同时浑浊度系数p增大和波长指数。的减小，可反应沙尘含量的增多和较大粒径含量的比例增大;并根据实际观测的沙尘粒子谱资料建立近地面层沙尘粒子的数浓度C。与p的正相关、沙尘粒子的空气动力学几何平均直径GMD与a的负相关关系。 产生沙尘暴的闽值风速在sms一，左右。沙尘暴的发生均伴随大、中尺度天气系统，主要是冷锋。从沙尘尺度谱和沙尘的沉降末速分析，出现沙尘暴，尤其是强沙尘暴时，系统中的上升气流可达每秒几米的量级，有时甚至更高。由于沙漠地表的热力强迫作用和地表的热力、动力的不均匀性，使得沙尘暴中的湍流输送比较强烈，加剧了尺度范围更广的沙尘粒子的向上输送。 沙漠和沙地上空，白天热力不稳定状态出现的频率高，超绝热梯度大，逆湿现象明显，净辐射主要用于发展湍流。在大、中尺度天气系统的上升运动的激发下，使不稳定层结积蓄的能量得以持续释放，发展对流运动，从而促使大量沙尘不断被卷起向上输送并随系统移运。大范围的强沙尘暴常发生于午后，其中沙漠地区强烈不稳定的热力层结特征是一个很重要的因素。 作为沙尘暴的物质源，其粒度组成、地表硬度、含水率，对沙尘暴的形成和强度变化有重要作用。 用三维区域欧拉长距离输送模式与新的东亚黄沙起动模式相祸合，来模拟1998年4月15一16日发生在北京的强的泥雨过程。沙尘粒子谱分为9个尺度档，MMS提供必要的气象条件。结果表明三维区域欧拉长距离输送模式与沙尘起沙模式结合，可以用来预报由抬升、输送、扩散和清除过程中的黄沙的浓度和尺度谱。观测结果与预报结果非常一致。输送过程的垂直分布清楚地表明小粒子在两个层次输送，一个接近地面，一个在对流层中层。黄沙的长距离输送和小雨是泥雨形成的原因。云物理和降水与来自沙尘粒子混合，尤其是小于Zpm的粒子，导致了华北地区泥雨的发生。更多还原

【Abstract】 Sandstorm is a frequent meso-scale disastrous event in spring over extensive north China. Asevere event may cause great losses of crops, livestock and human lives. Sandstorm acts as the primary source of sand aerosols. It is estimated that as high as two billion tons of such particles comes into air and, influencing radiation properties, cloud physics and environment, they exert strong impacts on the earth - air system and, particularly, the atmospheric environment.To investigate the space/time distributions and occurrence and evolution of such events, the diffusion pattern over deserts, turbulent transfer features in sandstorm weather, the particle size distribution, mass concentration and its distribution, optic properties, chemical composition and physical factors responsible for the initiation of raising sands, we made integrative observation and sounding of sandstorms deep in the large-scale desert area, including Tengri, Badanjilin and Maowusu, with the items consisting of micrometeorological measurement, 3D wind observation, data from KB-120 and Anderson samplers of mass concentrations of sands with their spectrum, the distribution of aerodynamic particle sizes from the APS3310A, retrieval of aerosols’ optic depth from sunphotometer data, assay of the chemical composition by means of Neutron Activiation Analysis (NAA) and integrated study of all related factors for causing sandstorm to occur, based on the observations of all kinds. And the "muddy rain" produced a single event of sandstorm is simulated in the context of a sand transfer model. From the above we come to the following conclusions.1) The number of sandstorm days from 12 weather stations in the Helanshan zone is documented, indicating that the events can happen on the east and west sides of the ranges all the year round, with high frequencies in April to May, averaging 3.2 and 3.1 days on the west side, respectively and with the eastern high frequency in April, averaging 2.0 days. Also, analysis reveals that the high frequency period for eastern station Yanchi and western Guaizihu is April, with 5.4 and 5.2 days, on average, respectively. Nine of the twelve stations have apparently reduced the number of sandstorm days, with the decreasing trend quite obvious, but an increasing trend is shown for three stations among them for the 1960s to the late 1980s, with severe and extremely severe events appreciably augmented during the 1960s to 1970s, a point that deserves our particular attention. Both on the east and west sides of the Helanshan Mountains the preferred frequency of such events happens between 14:00 to 20:00 (Beijing Time BT), with mean persistence depending strongly on the distance from station to source. And the shorter the distance, the longer the duration.2) From the analysis of the aerodynamic parameters and turbulent flux transfer under different synoptic conditions we achieve the conclusion that on sands raising and sandstorm days turbulent momentum and sensible-heat fluxes are important exchange factors in the boundary layer, with turbulent exchange stronger in sandstorm weather than both on fine and sand raising days. Prior tothe occurrence of such an event, in particular, the super-adiabatic instability in the near-surface boundary will reinforce sandstorm weather condition.3) Atmospheric turbulent diffusion parameters z and y have apparent daily variation. Under a clear sky, the vertical (horizontal) diffusion parameteroz (oy) peaks around 14:00 BT and valleys between 03:00 to 06:00 BT. Under a sandstorm sky great difference arises in their daily variation, depending on the starting time of a sandstorm. The zis smaller in diffusion speed compared to y, which shows a bigger range of daily variation. Mean wind, when smaller, has no distinct correspondence to the daily cycle of z and y.4) The number and mass concentration distributions of the background atmospheric sand particles of Ymchuan, Bayanhot and Tonggunur display a unimodal form, obeying a logarithmic normal distribution, greatly differing f更多还原