Spatial variation of cold front wind-driven circulation and quasi-steady state balance in Lake Pontchartrain Estuary
Spatial variation of cold front wind-driven circulation and quasi-steady state balance in Lake Pontchartrain Estuary
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DOI：
10.1016/j.ecss.2019.04.031
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发表时间：
2019-08
期刊：
影响因子：
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通讯作者：
Wei Huang;Chunyan Li
中科院分区：
文献类型：
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作者：
Wei Huang;Chunyan Li
在低盐度河口与限制开口到海洋的流通主要是由风驱动，并在较小程度上由开放边界的水位波动。数值模式实验进行了使用斜压有限体积社区海洋模式（FVCOM）的风驱动的环流在一段时间内，包括在庞恰特雷恩湖河口共16冷锋。这项工作的重点是检查的空间结构的环流响应当地和远程风。进一步分析了地面坡度和风应力之间的准稳态平衡。通过将FVCOM计算的表面斜率与稳态平衡方程的表面斜率进行比较来评估平衡的准确性。结果表明，这种平衡在跨河口方向比在沿河口方向更准确（R2 = 0.94 vs.0.60）。这种跨河口和沿河口方向之间准稳态平衡精度的差异是由开放边界引起的-存在潮汐引起的平均坡度。此外，即使去除潮汐效应，对于两个方向上的斜坡，精度仍然朝向开口端降低。远程风效应和剩余流量通过东部开放边界往往会引入偏离准稳态平衡在两个沿着和跨河口方向。由于底部摩擦，远距离风的影响减小到内部。局地风效应在沿岸、浅水区和海面产生顺风流，在近底层产生逆风流，这与正压风驱动环流的结果一致;而远风效应主要在开边界附近。此外，准稳态平衡是更准确的沿河口方向的冷锋通道之前，然后之后，因为风在该方向上的冷锋之前比之后相对较高的发生。相比之下，这种准稳态平衡在冷锋通道之前比之后在跨河口方向上不太准确，因为冷锋之前比之后在该方向上风的发生相对较低。
Circulation in a low-salinity estuary with restricted openings to the ocean is mainly driven by wind and to a lesser extent by water level fluctuations at the open boundaries. Numerical model experiments are conducted using a baroclinic Finite Volume Community Ocean Model (FVCOM) for wind-driven circulations during a period encompassing a total of 16 cold fronts in the Lake Pontchartrain Estuary. The work is focused on the examination of the spatial structure of circulation in response to local and remote winds. A quasi-steady state balance between the surface slope and wind stress is further analyzed. The accuracy of the balance is evaluated by comparing the FVCOM calculated surface slope with that from the steady state balance equation. Results show that this balance is more accurate in the cross-estuary direction than that in the along-estuary direction (R2∼ 0.94 vs. 0.60). This difference in the accuracy of the quasi-steady state balance between the cross- and along-estuary directions is caused by the open boundary - a tidally-induced mean slope exists. In addition, even if the tidal effect is removed, the accuracy still decreases toward the open end for slopes in both directions. Remote wind effect and residual flow through the eastern open boundary tend to introduce a departure from the quasi-steady state balance in both along- and cross-estuary directions. Remote wind effect decreases into the interior due to bottom friction. Local wind effect tends to produce downwind flows in coastal, shallow water regions and on the surface, but upwind flows near the bottom, a result consistent with barotropic wind-driven circulations; while the remote wind effect is important mostly near the open boundary. Furthermore, quasi-steady state balance is more accurate in the along-estuary direction before cold front passages then after, because of the relatively higher occurrence of the wind in that direction before the cold fronts than after. In contrast, this quasi-steady state balance is less accurate in the cross estuary direction before cold front passages than after, because of the relatively lower occurrence of the wind in that direction before the cold fronts than after.