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首页> 外文学位 >The influence of source landforms, antecedent precipitation, and winds on dust events in North Africa.
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The influence of source landforms, antecedent precipitation, and winds on dust events in North Africa.

机译：源地貌，前期降水和风对北非沙尘事件的影响。

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摘要

This dissertation identifies conditions associated with dust storms in North Africa. The introductory chapter frames a conceptual model of how atmospheric dustiness is governed by static landforms, dynamic characteristics of the surface (represented by cumulative antecedent precipitation or CAP), and surface wind fields. Visibility at 225 meteorological stations across Africa, north of 10° north latitude, is used as a proxy for atmospheric dust. A map of landforms is created from a multiple endmember mixture analysis of MODIS satellite imagery to represent landforms. The ten landforms identified are alluvial surfaces, dunes, dry lakebeds, water, basaltic surfaces, mountains, regs, bedrock surfaces, sandsheets, and vegetated surfaces. Climatological and event-based statistics are used to determine relationships between parameters related to visibility, landforms, CAP, and wind speed. CAP represents dynamic changes in the erodibility of the surface including the sheltering effect of vegetation and delivery of erodible sediments. Surface wind velocities represent the winds that mobilize fine sediments to become dust. Alluvial surfaces, dunes, dry lakebeds, regs, bedrock, and sandsheets are more often associated with low visibility (5 km) events than high. Negative correlations between median wind speed and the monthly frequency of visibility less than five kilometers (DEF-5) identify 33 stations where factors other than dust strongly influence the visibility record and these stations are removed. Results regarding the relationship between CAP and dustiness find that at Sahelian and southern Saharan locations, vulnerability to dust emissions is related to drought reducing vegetation cover. At central, northern, and eastern Saharan locations, vulnerability to dust emissions is related to wet conditions, probably as a result of fresh sediment being deposited at erodible locations in the landscape. Wind speed results find that for any dust source, there is an intermediate wind speed with minimum visibility, above which dispersion increases visibility and below which the wind is not strong enough to generate enough dust. Any study using dust measurements (visibility in this case) that are not close to the dust source will be characterizing the dust mobilization as well as the dust transport process so such measurements must be used with caution when trying to characterize dust sources.
机译：本文确定了与北非沙尘暴有关的条件。介绍性章节构成了一个概念模型，该模型说明了大气尘埃如何通过静态地形，地面的动态特性（以累积的前期降水或CAP表示）以及地面风场来控制。在北纬10°以北的非洲225个气象站的能见度被用作大气尘埃的替代物。通过对MODIS卫星图像进行多端元混合分析来创建地形图，以表示地形。确定的十个地貌是冲积面，沙丘，干lake的湖床，水，玄武岩面，山脉，雷格斯，基岩面，沙床和植被面。气候和基于事件的统计数据用于确定与能见度，地形，CAP和风速有关的参数之间的关系。 CAP代表了表面可蚀性的动态变化，包括植被的遮挡作用和可蚀性沉积物的输送。地表风速代表动员细小的沉积物变成灰尘的风。冲积层，沙丘，干lake的湖床，残渣，基岩和沙床通常比能见度低（<5 km）的事件多。中位风速与月度可见度小于5公里（DEF-5）之间的负相关关系确定了33个站，其中除尘埃以外的其他因素都对能见度记录产生了很大影响，这些站已被删除。关于CAP与尘土含量之间关系的结果发现，在萨赫勒地区和撒哈拉以南地区，粉尘排放的脆弱性与减少植被的干旱有关。在撒哈拉沙漠的中部，北部和东部地区，粉尘排放的脆弱性与潮湿条件有关，这很可能是由于新鲜沉积物沉积在景观中易受侵蚀的位置所致。风速结果发现，对于任何粉尘源，都存在一个中间风速，其可见度最小，在此范围内，分散会增加可见度，在此之下，风的强度不足以产生足够的灰尘。任何使用不靠近粉尘源的粉尘测量（在这种情况下为可见性）的研究都将表征粉尘的流动以及粉尘的运输过程，因此在尝试表征粉尘源时必须谨慎使用此类测量。

著录项

  • 作者

    Ballantine, John-Andrew Chapin.;

  • 作者单位

    University of California, Santa Barbara.;

  • 授予单位 University of California, Santa Barbara.;
  • 学科 Physical Geography.;Geology.;Atmospheric Sciences.
  • 学位 Ph.D.
  • 年度 2008
  • 页码 381 p.
  • 总页数 381
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 自然地理学;地质学;
  • 关键词

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