【作者】 陶健红；

【导师】 郑有飞；

【作者基本信息】 南京信息工程大学 ， 大气物理学与大气环境， 2007， 博士

【摘要】 西北地区是世界上沙尘天气的高发区之一，沙尘天气对生态环境的影响已经引起了社会和政府的高度重视。本论文主要通过统计、诊断分析和数值模拟的方法对西北地区的沙尘天气及其影响进行了探讨。研究结果表明西北地区沙尘天气的气候特征是：西北地区大部分地方年平均沙尘日数在5天以上，50天以上的沙尘发生高频区主要集中在沙漠及周边地区。沙尘活动春季频繁，秋季较少。近46年年沙尘日数趋势总体上呈显著下降，沙尘天气高发区下降趋势更为明显。70年代中期开始由较多期跃变为一个相对较少期。当北太平洋地区位势高度偏低，青藏高原至新疆500hPa高压脊异常偏强，亚洲大陆中高纬高度场较常年偏高时，西北地区沙尘日数偏少，反之亦然。当春季太平洋海温表现为厄尔尼诺（拉尼娜）典型态时，同期沙尘日数偏少（多）。通过沙尘暴天气的天气学特点的诊断和模拟分析，找出沙尘天气的预报着眼点：伴随着强冷空气的入侵，地面蒙古气旋及其冷锋的强烈发展，中尺度切变线触发了沙尘活动。强沙尘暴发生在200hPa高空急流中心前部的出口区右侧。沙尘暴发生在不稳定的大气层结中，沙尘暴伴随有能量的积聚和释放过程。CUACE-Dust沙尘模式系统对沙尘天气有一定的预报能力。螺旋度反映了沙尘暴附近的动力场特征，将水平螺旋度、垂直螺旋度二者有机地结合在一起，可为沙尘暴预报提供参考依据，使沙尘暴天气的预报更具针对性。一方面，水平螺旋度更具预报指示性，另一方面，垂直螺旋度更倾向于反映系统的维持状况和系统发展、天气现象的剧烈程度。沙尘暴区上空垂直螺旋度的垂直分布为中高层负值，低层正值。随着正垂直螺旋度的加强且高度抬高，沙尘暴发展愈强烈。从时间演变上看，水平螺旋度正值区的加强时间超前于沙尘暴的发生。研究认为，沙尘天气对环境（空气质量、酸雨、辐射）有明显的影响。春季河西沙尘发生次数与同期兰州PM₁₀浓度呈显著正相关。通过定义指数的方法来定量评估河西沙尘活动对空气质量造成的影响，结果表明，兰州年度（3月，4月）PM₁₀质量浓度中的8.8％（13.9％，23.1％）是河西走廊沙尘活动向兰州输送PM₁₀颗粒的结果。青藏高原东北侧酸雨空间分布受沙尘的影响，沙尘活动频繁地区的降水pH值基本呈弱碱性或中性。沙尘较多的春季产生酸雨的概率小。沙尘活动可以使兰州、西峰站的降水pH值增加0.7。沙尘活动期间，大气浑浊度明显增加，沙尘活动对太阳辐射有明显的影响。与晴空日相比较，沙尘的散射辐射增加12.66-18.00％，净辐射下降6.68-45.79％、总辐射下降12.97-47.80％、反射辐射下降13.19-57.49％，直接辐射下降47.81-87.45％。在沙尘暴强盛期，各种辐射的强度都有显著的下降，对应的地面气温也有明显的下降。更多还原

【Abstract】 As one of the areas with frequent sand-dust event occurrences,The effect ofsand-dust events on coo-environment of Northwest China have been highly regarded bythe government and the whole society. On the basis of the statistics, diagnosis, andnumerical simulation, the sand-dust weather of Northwest China is studied.Results show that the climatic characteristics of sand-dust events in the NorthwestChina are: the numbers of sand dust days in the most part of the Northwest China ismore than 5 days. The high frequency areas with sand-dust occurrence days more than50 days are mainly in the deserts and their surroundings. The events are frequent inspring and scarce in autumn. The occurrence days of sand-dust in the last four decadesappears a generally decrease trend which is more significant in the high frequency areas.There is a transform from a relative frequent period to a relative scarce period in themiddle 1970s. The negative anomaly of sand dust days in the Northwest chinacompanied with the negative anomaly of geopotential height in the north Pacific, theabnormal strong 500hpa ridge of high pressure, and the abnormal high geopotentialheight field in the extratropical latitude of Asia, and vice versa. The typical EL Nine （LaNina）style of the sea surface temperature in spring of Pacific consist with thenegative（positive） anomaly of sand dust days in the same period.The key points of the sand-dust event prediction is obtained by use of thediagnosis, numerical analysis, and the synoptic characteristics of sand-storm weather:the sand dust event is triggered by the strong upper cold air, the vigorous developmentof the surface Mongolia cycle and its cold front, and the meso-scale shear-line. Intensesand storms occur in the right side of the front area of front part of 200hPa upper air jetstream center. Sand-storms appear in the unstable atmospheric stratification, wherein theevent companied with accumulation and release process of energy. CUACE-Dust modelsystem has the forecast ability of sand dust weather event.Helicity reflect the characteristics of dynamic field near the sandstorm, and thecombination of the horizontal and vertical helicity can provide instruction in sand-stormprediction, and pertinence to the prediction. On the one hand, the horizontal helicity hasmore instructive meaning for prediction, on the other hand, the vertical helicity canmore reflect the maintenance and development of the system, as well as the acuteextend of the synoptic phenomenal. The distribution of helicity over the sandstorm areawas negative at higher levels and positive at lower levels. The heavier is the sandstormas the positive helicity enhanced and the height increased. Strengthen of the positivevalue area of horizontal helicity occurred earlier than the sand-storm.Results show: sand-storm events have evident effect on the environments, such asair quality, acid rain, and radiation. Frequency of sand dust event in spring of Hexicorridor is positive relate to the PM₁₀ concentration in Lanzhou. Analysis via definition of index present that the 8.8% （13.9%, 23.1%） of the yearly（March, April） PM₁₀ massconcentration is the result of the PM₁₀ transportation from sand dust event of Hexicorridor to Lanzhou. The spatial distribution of acid rain in the northeast Qinghai-TibetPlateau is influenCed by sand dust, with the weak alkali or neutral pH value for theprecipitation in the high frequency areas with sand-dust. The small probability for acidaccompanied with relative more sand-dust in spring. The sand-dust events in Lanzhouand Xifeng stations can make pH value increased 0.7.During sand-dust events, turbidity of atmosphere increased significantly and theevents apparently influenCed the solar radiation. Scatter radiation increased12.66-18.00%, with net radiation, total radiation, reflection radiation and directradiation deCreased 6.68-45.79%,12.97-47.80%,13.19-57.49% and 47.81-87.45%,respectively, with respect to the clear sky. Strength of every radiation decreasedevidently in the vigorous period of sand-storm, with the significant decrease ofcorresponding surface temperature.更多还原