Observations of the Nocturnal Boundary Layer Associated with the West African Monsoon
Observations of the Nocturnal Boundary Layer Associated with the West African Monsoon
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DOI：
10.1175/2010mwr3287.1
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发表时间：
2010-08-01
影响因子：
3.2
通讯作者：
Guichard, Francoise
中科院分区：
文献类型：
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作者：
Bain, Caroline L.;Parker, Douglas J.;Guichard, Francoise
获得并分析了2005年8月萨赫勒中部（北纬15.2度，西经1.3度）的一组夜间系留气球和风筝测量结果。利用边界层高度标准化测量的高度，产生了所有夜晚数据的合成。观测结果显示了夜间边界层发展的一些典型特征，特别是日落后强烈的逆温和夜间晚些时候形成的低空夜间急流。在大多数夜晚，所采样的急流在夜间没有明显的方向变化，边界层热力结构从一个晚上到另一个晚上表现出一定的变化。这是使用两个对比的案例研究期间进行调查。其中一个个案（2005年8月18日）显示，低层风向在夜间显著改变。这一变化被两个大尺度模式很好地捕捉到，表明大尺度动力学对当晚的边界层风有显著影响。对于这两个案例研究，模型往往低估近地面风速在夜间，这是一个功能，可能会导致低估的水分通量向北的模型。
A set of nighttime tethered balloon and kite measurements from the central Sahel (15.2 degrees N, 1.3 degrees W) in August 2005 were acquired and analyzed. A composite of all the nights' data was produced using boundary layer height to normalize measured altitudes. The observations showed some typical characteristics of nocturnal boundary layer development, notably a strong inversion after sunset and the formation of a low-level nocturnal jet later in the night. On most nights, the sampled jet did not change direction significantly during the night.The boundary layer thermodynamic structure displayed some variations from one night to the next. This was investigated using two contrasting case studies from the period. In one of these case studies (18 August 2005), the low-level wind direction changed significantly during the night. This change was captured well by two large-scale models, suggesting that the large-scale dynamics had a significant impact on boundary layer winds on this night. For both case studies, the models tended to underestimate near-surface wind speeds during the night, which is a feature that may lead to an underestimation of moisture flux northward by models.