Physical processes controlling the formation, evolution, and perturbation of the low‐salinity front in the inner shelf off the southeastern United States: A modeling study
Physical processes controlling the formation, evolution, and perturbation of the low‐salinity front in the inner shelf off the southeastern United States: A modeling study
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DOI：
10.1029/1998jc900040
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发表时间：
1999-01
影响因子：
--
通讯作者：
Changsheng Chen;Lianyuan Zheng;J. Blanton
中科院分区：
文献类型：
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作者：
Changsheng Chen;Lianyuan Zheng;J. Blanton
利用全三维原始方程和湍流闭合模型，研究了控制南大西洋湾内陆架低盐度锋形成、演化和扰动的物理过程。该模式受半日潮（M2、S2和N2）、多河流量气候资料和上升流有利风的影响。该模式对半日潮的两周和月变化提供了合理的模拟。计算所得的潮汐幅值和相值与沿岸测潮站的观测资料吻合良好。分层潮汐整流对浮力流的空间结构有显著的改变。因此，向南残余流在锋面明显增强，靠近海岸处减弱或逆转。在每条河流的下游区域形成一个弱流速区，它阻挡了低盐度的水，在内陆架形成了多个“舌状”圆顶。对于给定的春季气候上升流有利风，孤立的低盐度透镜可以分两步形成。首先，由于潮汐、多种河流流量和有利于上升流的风之间的相互作用，在锋面区外缘形成一个几何上控制的波状锋面形状。然后，当波峰靠岸一侧的水被来自波峰南部上游槽的相对高盐度的水平流取代并从较深区域向上扩散时，在波峰形成孤立的低盐度透镜。在南大西洋湾内陆架上，在河流排放和有利于上升流的风的气候条件下，风致上升流在孤立透镜体的形成中起不了关键作用。
Physical processes that control the formation, evolution, and perturbation of the low-salinity front over the inner shelf of the South Atlantic Bight have been examined using a fully three-dimensional primitive equation and turbulent closure model. The model was forced by semidiurnal tides (M2, S2, and N2), climatological means of multiple river discharges, and upwelling-favorable wind. This model has provided a reasonable simulation of the fortnightly and monthly variations of semidiurnal tides. Computed amplitudes and phases of tides show good agreement with observational data available at tidal gauge stations along the coast. Spatial structures of buoyancy currents are significantly modified by stratified tidal rectification. As a result, the southward residual current intensifies significantly at the front and reduces or reverses close to the coast. A weak velocity area forms in the downstream region of each river, which blocks the low-salinity water to form multiple “tongue-like” domes in the inner shelf. For a given springtime climatological upwelling-favorable wind, isolated low-salinity lenses can form episodically in two steps. At first, a geometrically controlling wave-like frontal shape develops at the outer edge of the frontal zone as a result of the interaction between tides, multiple river discharges, and upwelling-favorable wind. Then, isolated low-salinity lenses form at the crest when water on the shoreward side of the crest is displaced by relatively high salinity water advected from the upstream trough south of the crest and diffused upward from the deeper region. Wind-induced upwelling is noticeable to compensate for the water loss due to the near-surface offshore Ekman transport, but it does not play a critical role in the formation of isolated lenses under the climatological conditions of river discharges and upwelling-favorable winds over the inner shelf of the South Atlantic Bight.