Emergence and growth of sand dunes results from the dynamic interaction between topography, wind flow and sediment transport. While feedbacks between these variables are well studied at the scale of a single and relatively small dune, the average effect of a periodic large-scale dune pattern on atmospheric flows remains poorly constrained, due to a pressing lack of data in major sand seas. Here, we compare local measurements of surface winds to the predictions of the ERA5-Land climate reanalysis at four locations in Namibia, both within and outside the giant linear dune field of the Namib Sand Sea. In the desert plains to the north of the sand sea, observations and predictions agree well. This is also the case in the interdune areas of the sand sea during the day. During the night, however, an additional wind component aligned with the giant dune orientation is measured, in contrast to the easterly wind predicted by the ERA5-Land reanalysis. For the given dune orientation and measured wind regime, we link the observed wind deviation (over \(50^{\circ }\)) to the daily cycle of the turbulent atmospheric boundary layer. During the night, a shallow boundary layer induces a flow confinement above the giant dunes, resulting in large flow deviations, especially for the slower easterly winds. During the day, the feedback of the giant dunes on the atmospheric flow is much weaker due to the thicker boundary layer and higher wind speeds. Finally, we propose that the confinement mechanism and the associated wind deflections induced by giant dunes could explain the development of smaller-scale secondary dunes, which elongate obliquely in the interdune areas of the primary dune pattern.

沙丘的出现和生长是地形、风流和泥沙输送之间动态相互作用的结果。虽然这些变量之间的反馈在单个和相对较小的沙丘的尺度上得到了很好的研究，但由于主要沙海中数据的迫切缺乏，周期性的大尺度沙丘模式对大气流动的平均影响仍然很有限。在这里，我们将当地表面风的测量结果与纳米比亚四个地点的 ERA5-Land 气候再分析的预测进行比较，这些地点包括纳米布沙海的巨大线性沙丘场内外。在沙海以北的沙漠平原，观测和预测非常吻合。白天的沙海沙丘间地区也是如此。然而，在夜间，与 ERA5-Land 再分析预测的东风形成对比，测量了与巨型沙丘方向对齐的额外风分量。对于给定的沙丘方向和测量的风态，我们将观测到的风偏差（超过\(50^{\circ }\) ) 到湍流大气边界层的每日周期。在夜间，较浅的边界层在巨型沙丘上方引起流量限制，导致流量偏差较大，尤其是对于较慢的东风。白天，由于边界层较厚，风速较高，巨型沙丘对大气流动的反馈要弱得多。最后，我们提出由巨型沙丘引起的限制机制和相关的风偏转可以解释较小规模的次级沙丘的发展，这些沙丘在初级沙丘模式的丘间区域倾斜伸长。