【作者】 岳平；

【导师】 牛生杰；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2006， 硕士

【摘要】 沙尘暴是我国北方地区的主要自然灾害之一。自公元前16世纪以来,我国史书、地方志等对沙尘现象就有记载或叙述。近年来,频繁发生的沙尘暴天气所导致的气候效应、生态环境效应、对社会经济发展和社会生产安全带来的负面影响及其对人类身心健康的影响越来越受到广泛的关注。本文主要目的是研究沙尘暴过程气象要素变化特征及其内部热力结构。 研究方法和研究内容如下:1) 引入了相对地面螺旋度对我国西北地区,尤其是对河西走廊沙尘暴期间的相对地面螺旋度进行了分析,并与相对地面螺旋度进行了对比分析;2)应用“3θ”(位温、假相当位温和饱和相当位温)曲线及其变化特征对沙尘暴期间大气热力稳定度进行了诊断分析;3) 通过加密探空,对沙尘暴期间气象要素的垂直分布特征进行了研究;4) 利用自动气象站观测每分钟的气象要素值,对比分析了春夏不同季节沙尘暴期间地面微气象要素的变化特征;5) 在对沙尘暴宏微观特征深入研究的基础上,利用沙尘暴热力模型,分析了对流体激发的强沙尘暴的垂运动速度和切向旋转速度。 本文的研究结果表明: 1) 利用温度平流与相对地面螺旋度之间的关系比较容易得出天气系统所经区域螺旋度的值,但相对地面螺旋度的计算结果依赖于对天气系统的准确分析,尤其是水平温度梯度的判断;相对风暴螺旋度的强中心与沙尘暴的强中心有很好的对应关系。 2) “3θ”曲线及其变化特征表明,沙尘暴来临前大气层结处于超绝热状态,沙尘暴过境的前半期,大气温湿结构分布有利于沙尘暴的发生、发展。沙尘暴过境的后期,大气层结调整到稳定状态,抑制了干对流的发展;沙尘暴前期,大气整层湿度较小,随着高空槽逼近,高空首先出现增湿度现象,随后水汽由高空向低层输送,整层大气相对湿度增加。 3) 对2004年3月28日和7月12日发生在甘肃酒泉的两次沙尘暴过境时地面微气象要素的变化特征对比后发现:两次沙尘暴发生前地面湿度都较小,气压较低,但是在临近发生时地面气压会猛增,接着维持一段时间的相对稳定状态,但春季沙尘暴过程这个时间更长;沙尘暴即将结束时地面气压再次大幅增加。沙尘暴发生前气温偏高,结束后较短时间气温会出现急剧下降;春季沙尘暴期间0cm地温和气温的变化趋势比较一致,但是5cm地温的变化趋势与气温变化差别较大;夏季沙尘暴过程中0cm、5cm地温的变化趋势与气温变化趋势都非常接近比较一致。 4) 热机自然对流理论能够很好地用来研究沙尘暴内部热力动力结构,特别是其内部中小尺度强对流系统的分析和研究,可以更进一步的加深对沙尘暴强度变化和形成机理的认识。强沙尘暴的形成与发展,不仅与环境风速有关,而且与沙尘内部中小尺度气旋自身的强度,特别是切向旋转速度和垂直运动速度的大小密切相关。利用酒泉站探空资料计算出的沙尘暴对流体的最大切向旋转速度为11.4m/s,垂直运动速度为14.0m/s;更多还原

【Abstract】 Sandstorms is one of the major natural disasters in north China region. Since 16 centuries BC, sand-dust phenomenon is documented or described in history books. In recent years, frequent sandstorms weather and climate effects, the effects of the ecological environment, the production of socio-economic development and social security, as well as the negative impact on human health effects caused by sandstorms are widely concerned. In this paper we study the character variations of meteorological parameters during the dust-storm and the thermo-dynamical structure.The method and content as following: (1) Helicity were introduced and used to study sandstorms in north-west China , especially Relative Earth Helicity and Relative Storm Helicity were applied to diagnosis the severe dust-storm in summer in Hexi Corridor. (2) Thermal stability during sandstorms were diagnoses by application of "3θ" curve and change characteristics of atmospheric. (3)The vertical parameters distribution of sandstorms are studied by use encryption sounding data. (4)Per minute data in the season of spring and summer sand-storms, which observed by automatic weather station, were used to analysis the meteorological parameters during dust-storm . (5)Basis on the study of sandstorms microscopic characteristics of sandstorms, thermal-dynamical model is used to computer the convective of sandstorms’ tangential velocity and vertical velocity . The main results show as following:(1) Relative Earth Helicity and Relative Storm Helicity were applied to diagnosis the severe dust-storm in summer. There is a close relationship between thermal advection and Relative Earth Helicity, but this kind of helicity values closely relates to exactly analysis and diagnosis the intensity of weather system, especially the horizontal temperature gradient. Relative Storm Helicity high values center has a good homologous to the dust-storms severe areas.(2) Using high detective data over Minqin and Jiuquan base station in Hexi corridor of Gansu province, 3~θ variations were analyzed. The results show that the atmosphere stratification is hot and dry before the dust-storm, but cold and wet at the end of the sandstorm. The stratification is also beneficial to occur dust-storm at adjust phases, but adjusts to stable state at the end phases of dust-storm. Before sandstorm happened, the layer of atmospheric humidity is small. With the trough is approaching, humidity is increased in high levels and thehumidity transmission to the lower levels in the following time, the atmospheric layer relative humidity is increased.(3) Using the per minute surface meteorological parameter data of the twice sandstorms cases recorded by sandstorm automatic observation system of Jiuquan base station on March 28 and on July 12 of 2004 , the micro meteorological element change characteristic were analyzed . The result indicated that, the surface humidity and barometric pressure are both quite low before sandstorms explode. Surface pressure increases suddenly in the beginning course of the twice sandstorms, then maintains a period of relatively steady states. But the relatively steady period is longer in the spring sandstorm case than winter’s. The surface pressure largely increases once again before sandstorms nearly finished. The surface air temperature is high before sandstorms happened, but decrease quickly at the end of the course. In the spring sandstorm period, Ocm depth earth temperature and surface air temperature change tendency quite consistent. But in summer not only Ocm depth earth temperature but the 5cm depth earth temperature variation is consistent with surface air temperature change tendency. Owning to the difference of the surface characters in different seasons , the horizontal visibility of summer case is bad than the spring courses, although the horizontal wind speed of the spring occurs is obviously bigger than the summer sandstorms.(4) According to the theory of natural convection as a engine proposed by Renn o and Ingersoll in 1996, the thermodynamical structure of a dust-storm were analyzed , which occurred in the Jjiuquan area of Gansu Province at 20 on July 12, 2004. The result shows that the air near the surface is in the dryness and heat condition, and there is extreme low temperature between 200hpa and 300hpa levels. The huge vertical temperature gradient of atmosphere is benefit to dry convection. The intensity of the dust-storm is closely related to the tangential and vertical velocity of the micro-scale and meso-scale convections. The tangential velocity and vertical velocity according to computation are close to the foreign stiu observation results. The tangential velocity is 11.4m/s and vertical velocity is 14m/s according to computation, but the maximal surrounding’s velocity, memorized by the dust-storm observational system, is only 9.3m/s.更多还原