Dust mobilization due to density currents in the Atlas region:: Observations from the Saharan Mineral Dust Experiment 2006 field campaign
Dust mobilization due to density currents in the Atlas region:: Observations from the Saharan Mineral Dust Experiment 2006 field campaign
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DOI：
10.1029/2007jd008774
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发表时间：
2007-11-15
影响因子：
4.4
通讯作者：
Schuetz, L.
中科院分区：
文献类型：
--
作者：
Knippertz, P.;Deutscher, C.;Schuetz, L.
降水蒸发是干旱和炎热沙漠环境中普遍存在的特征。由此产生的冷却通常会产生高密度的气流，并在其前缘产生强烈的湍流，这可以调动大量的灰尘。山脉通过触发对流、冷空气下坡加速以及通过水的作用促进山麓细粒沉积物的积累来支持这一过程。对于世界上最大的沙尘源撒哈拉来说，由于缺乏足够高分辨率的观测数据，对这种机制的研究很少。本研究利用2006年5月/ 6月撒哈拉矿物粉尘实验（SAMUM）野外活动期间收集的独特数据集，证明了摩洛哥南部阿特拉斯山脉撒哈拉一侧密度流的频繁发生。密度流与下午山区上空的对流有关，其寿命约为10小时。有时长达数百公里的尖锐前沿通过时，通常伴随着露点和风速的显著增加、风向的改变以及因悬浮尘埃而导致的温度和能见度的降低。可以想象，这一机制与暖季北非其他山区有关。这意味着用数值模式模拟沙尘循环需要一个可靠的湿对流过程的表示，以便产生来自撒哈拉沙漠的真实沙尘排放。
[1] Evaporation of precipitation is a ubiquitous feature of dry and hot desert environments. The resulting cooling often generates density currents with strong turbulent winds along their leading edges, which can mobilize large amounts of dust. Mountains support this process by triggering convection, by downslope acceleration of the cool air, and by fostering the accumulation of fine-grained sediments along their foothills through the action of water. For the Sahara, the world's largest dust source, this mechanism has been little studied because of the lack of sufficiently high resolution observational data. The present study demonstrates the frequent occurrence of density currents along the Sahara side of the Atlas Mountain chain in southern Morocco using the unique data set collected during the Saharan Mineral Dust Experiment (SAMUM) field campaign in May/June 2006. The density currents are related to convection over the mountains in the afternoon hours and have lifetimes on the order of 10 h. The passage of the sharp leading edge that sometimes reaches several hundred kilometers in length is usually associated with a marked increase in dew point and wind speed, a change in wind direction, and a decrease in temperature and visibility due to suspended dust. It is conceivable that this mechanism is relevant for other mountainous regions in northern Africa during the warm season. This would imply that simulations of the dust cycle with numerical models need a reliable representation of moist convective processes in order to generate realistic dust emissions from the Sahara.