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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Coastal foredune topography as a control on secondary airflow regimes under offshore winds
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Coastal foredune topography as a control on secondary airflow regimes under offshore winds

机译：沿海福地地形作为对海上风作用下二次气流状态的控制

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摘要

Aeolian sediment transport under offshore winds is usually discounted from sediment budget considerations of coastal dunes. Results presented here indicate however, that depending on wind orientation and foredune morphology, positive contributions to the sediment budget can arise from offshore winds. Lee-side airflow patterns, seaward of the foredune crest, under offshore winds were studied at three sites of varying foredune geometry along Magilligan Strand, Northern Ireland. Ultrasonic anemometers recorded 1 Hz wind velocity data at 1 degrees intervals. Descriptive statistics and wind rose diagrams were used in the analysis of these data. Under perpendicularly offshore winds each site exhibited a different type of lee-side airflow pattern. A tall (11.4 m), sharp-crested foredune produced flow separation with a recirculation cell. A lower (6.6 m), more rounded, foredune crest exhibited lee-side flow that remained attached but was deflected parallel to the crest, while flow over a low incipient foredune crest resulted in attached flow with no deflection in the lee. The morphology of the lee slopes best explained these airflow adjustments. More obliquely offshore winds were also found to affect the secondary airflow patterns, with a smooth transition from flow separation to flow attachment as the incident angle decreased. At higher wind velocities this smooth transition was replaced with a more abrupt switch between the secondary airflow types. This threshold was located at similar approach angles to those recorded for desert dunes (90 degrees +/- 20 degrees). These findings have significant implications for the post-storm recovery and long-term evolution of beach-dune systems where the predominant winds are offshore, and offer an explanation for the presence of many beach-dune systems in lee-coast locations.
机译：通常考虑到沿海沙丘的沉积物预算因素，海上风下的风沙沉积物运输通常会被打折。但是，这里给出的结果表明，根据风向和前缘形态，海上风能会对沉积物收支产生积极贡献。研究人员在北爱尔兰马吉利根海峡的三个不同船首几何形状的地点研究了在海上风的作用下，前船rest向海的李方气流模式。超声波风速仪以1度间隔记录1 Hz风速数据。描述性统计数据和风向图用于分析这些数据。在垂直海上风的作用下，每个站点都表现出不同类型的背风面风型。高度高（11.4 m），尖顶的虎皮鱼与再循环池产生了流动分离。较低的（6.6 m），圆形，前额峰显示出背侧流，该流保持附着，但与峰平行地偏转，而在较低的前额峰上的流导致附着流，而在背中没有偏转。背风坡的形态最能解释这些气流调节。还发现更倾斜的近海风会影响二次气流模式，随着入射角的减小，从气流分离到气流附着的平稳过渡。在较高的风速下，这种平稳的过渡被次级气流类型之间更突然的切换所代替。该阈值位于与沙漠沙丘记录的接近角（90度+/- 20度）。这些发现对暴风雨后的恢复和海滩沙丘系统的长期演变具有重要意义，在这些海滩沙丘系统中主要风是在海上，并为背风地区存在许多海滩沙丘系统提供了解释。

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