【作者】 沈洁；

【导师】 李耀辉；

【作者基本信息】 兰州大学 ， 气象学， 2011， 硕士

【摘要】 沙尘暴是恶劣的自然环境与大气异常运动共同作用的结果,是一种危害性极强的灾害性天气。我国西北不同区域沙尘暴的发生发展具有地域特征,民勤县地处巴丹吉林和腾格里两大沙漠的接壤地带,正好位于雅布赖山和龙首山形成的山口下方。有利的地形和丰富的沙尘源,加之又是我国西北路径冷空气的必经之地,使得民勤成为河西走廊沙尘暴的重点发生区。本文研究的目的是利用实际观测资料、GRAPES-SDM沙尘暴模式,分析2010年4月24日发生在民勤地区一次特强沙尘暴的特征,以及通过修改模式中的地形参数,对民勤周边地形做出调整,进而分析地形对沙尘暴天气过程的影响。首先利用实况观测资料对2010年4月24日我国河西走廊民勤出现的区域性特强沙尘暴过程进行天气分析,结果表明：1)乌山脊前低槽、高空急流、地面热低压、地面冷锋等是形成此次特强沙尘暴的主要天气系统,强温度梯度和大气斜压性为沙尘的扬起提供起始动能。2)本次特强沙尘暴过境民勤前,地面处于热低压系统的干暖状态中,地面水平风风向有波动,风速有加大趋势；过境期间,能见度急剧下降,气压升高,3h变压差值增大,温度急剧下降,相对湿度增加,风速迅速增大达到最大值；过境后短时间内,气温持续下降,相对湿度增加,能见度增大,风速有减小趋势且风向少变。3)垂直速度、螺旋度的变化与沙尘暴的发生发展联系密切,同时也能反映出沙尘暴的强度变化。其次利用GRAPES-SDM沙尘模式对民勤周边山地采取三种不同方案(削减山高一倍；增加山高一倍；移动山地)修改地形进行敏感性试验,主要从风速、地面起沙通量及沙尘输送方面进行分析,并与控制实验对比,研究结果表明：1)地形高度降低,单站风速较控制试验增大,携沙气流遇到地形阻挡,沿着坡地爬升,部分沙尘可以翻越地形到背风坡,此时的地形特征将减弱沙尘扩散强度2)地形高度增高,单站风速随时间变化整体为增加趋势,气流发生明显的绕流,改变沙尘扩散方向3)地形移动,单站风速整体趋势增大,民勤地区沙尘暴影响范围减小,沙尘浓度值减小,整体影响强度减弱,沙尘影响范围较控制试验向南及东南方向扩展。4)在相同时间段内,三种地形敏感性试验模拟沙尘通量值要低于控制试验中的数值,其中减少最多的是抬升山地方案。更多还原

【Abstract】 Sandstorm is a hazardous strong severe weather which is the result of the interaction of the bad natural environment and anomaly atmospheric movement. The different areas in the northwest sandstonn occur with local characteristics, MinQin is located on the boundary of Badan Jara and Tenger Desert, and just located on the beneath mountain pass which is fonned by Jas cloth Lai and Longshou Mountain. This advantageous terrain and abundant dust source, plus it is the only way which must be passed of cold air of northwest China, leading to MinQin became the key area of sandstorm occurring in HeXi Corridor.The purpose of this study is to use the actual observation data and GRAPES_SDM sandstorm model, analyzes a particularly strong sandstorm which occurred in MinQin on April 24th 2010, and through the modification of the terrain parameter of the model to make adjustments the surrounding terrain of MinQin, then analyzes the terrain effection in the process of sandstonn.Firstly, based on the live observation data of April 24,2010 to analyse one process of regional strong sandstorm weather which appeared in Minqin in the Hexi Corridor The results show that:1) This heavy dust storm weather mainly touched off by Ural low trough before ridge, high level jet stream, surface thermal pressure and cold front etc, for sand storm,strong temperature gradient and atmosphere baroclinic provided initial energy motion.2) During this heavy dust storm process, Polar dry cold air was transported to the trough under a strongly and northerly airstream which is after Ural trough,so the low trough deepens and frontal zone before trough strengthen, as the pressure and temperature gradient increased resulting in the deep and strong ascending motion which was the large-scale circulation field of the dust storm. Before this heavy dust storm coming, the air temperature rose gradually, relative humidity sharply descend, the surface in thermal low pressure of dry and warm conditions, the wind directions experienced difference phases and increased, the ground temperature also increased; visibility and air temperature sharply decreased during the sandstorm, at the same time,the difference of 3 time-varying pressure rose with the pressure increased, relative humidity increased and the wind speed reached the peak value; after a short time passing, with the long-wave radiation strengthen because of the upper level cold advection and the dust weather weakening, which was leading to the air temperature consecutive drops, relative humidity and visibility increased, the wind speed declined with the little change of directions.3) Beyond that the sandstorm was very much involved with the alteration of vertical velocity and helicity that they could reflect the change of strength of sandstorm.Secondly, using a dust model GRAPES SDM to simulation the terrain filed of this process through three ways of changing terrain and according to the special terrain of MinQin, then mainly analysed by wind speed, surface dust emission, dust transportation and compared to the values of control experiment, the result shows that:1)Firstly found that when lowered terrain level, wind speed of one site was higher than control experiment, this type terrain would weaken the diffusion intensity.2)Secondly the wind speed of site increased with the varying time when heightened the terrain, the spreading of dust storm was changed owing to this terrain.3)Finally, the wind speed obviously increased when removing the terrain, the spreading of dust storm in MinQin and the whole region where the value also declined was weakened but expansion of south and southeast direction compared to the control test.4)During the same time the simulation value of dust emission of three types experiment were less than the control test, and the least one was upraising of the mountain.更多还原