A modeling study of shelf circulation off northern California in the region of the Coastal Ocean Dynamics Experiment: Response to relaxation of upwelling winds
A modeling study of shelf circulation off northern California in the region of the Coastal Ocean Dynamics Experiment: Response to relaxation of upwelling winds
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DOI：
10.1029/2000jc000768
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发表时间：
2002-09-01
影响因子：
3.6
通讯作者：
Allen, JS
中科院分区：
文献类型：
--
作者：
Gan, JP;Allen, JS
[1]本文对沿海海洋动力学实验（CODE）区域（37 ° ~ 40 ° N）内北方加州外陆架的风强迫流进行了两部分模拟研究。本文是一个以过程为导向的研究与理想化的风应力强迫。Gan和艾伦[2002]涉及1982年4 - 5月观测风和热通量的强迫以及模式结果与CODE观测的比较。一个特征，但以前无法解释的，在CODE期间观察到的响应减弱，或放松，向南上升流有利的风是时间依赖性的发展，向北流的内大陆架旁边的海岸。北风的存在不是发生这种情况的必要条件。本文的目的是研究在理想条件下，陆架流响应上升流风松弛事件的动力学。在基本的情况下，实验空间均匀的上升流有利的南风应力为0.1帕施加到海洋最初在休息。应力保持恒定10天，然后在3天内线性降低至零。响应于向南风的应力，向南的沿岸流在陆架上发展，伴随着海岸附近的冷的、稠密的水的上涌。相当大的空间变异性的陆架流，显然与沿岸的海岸线和底部地形的变化，被发现。沿岸电流往往从海角以南的海岸分离，最冷的地表水被发现在这些位置。随着风力的减弱，与观测到的相似，向北的海流在许多沿岸位置靠近海岸的内大陆架上发展。沿岸动量平衡的检查表明，北向流是由与负沿岸压力梯度相关的北向压力梯度力推动的。这些压力梯度是由风强迫流动与陆架地形的沿岸变化相互作用而形成的。总体上，负的沿岸压力梯度在Pt附近增强。Reyes和Pt。竞技场受梯度风平衡，均为海角以南。负压梯度在地转上平衡了深处的陆上流动，并且这些位置的上升流得到加强。在海角以北，正气压梯度主要与非线性平流作用相平衡，风停止后，强迫的跨陆架环流减弱，海角以南产生的不平衡的负气压梯度加速了沿岸流向北流动。Gan和艾伦[2002]在对观测到的时变风的更复杂的沿海海洋响应中发现了具有类似动力学的过程。
[1] A two-part modeling study of the wind-forced flow on the continental shelf off northern California in the region (37degrees-40degrees N) of the Coastal Ocean Dynamics Experiment (CODE) is pursued. This paper involves a process-oriented study with idealized wind stress forcing. Gan and Allen [2002] involves forcing with observed winds and heat flux for April-May 1982 and comparison of model results with CODE observations. A characteristic, but previously unexplained, response observed during CODE following the weakening, or relaxation, of southward upwelling favorable winds is the time-dependent development of northward currents over the inner shelf next to the coast. The presence of northward winds is not necessary for this occurrence. The objective in this paper is to investigate the dynamics of the shelf flow response to upwelling wind relaxation events under idealized conditions. In the basic case experiment a spatially uniform upwelling favorable southward wind stress of 0.1 Pa is applied to the ocean initially at rest. The stress is held constant for 10 days and then decreased linearly to zero over 3 days. In response to the southward wind stress, southward alongshore currents develop on the shelf accompanied by upwelling of cold, dense water near the coast. Considerable spatial variability in the shelf flow, clearly related to the alongshore variations in coastline and bottom topography, is found. The alongshore currents tend to separate from the coast south of capes, and the coldest surface water is found at those locations. As the winds decrease, northward currents, similar to those observed, develop on the inner shelf next to the coast at many alongshore locations. Examination of the alongshore momentum balances shows that the northward currents are forced by a northward pressure gradient force associated with negative alongshore pressure gradients. These pressure gradients are set up by the interaction of the wind-forced flow with the alongshore variations in shelf topography. In general, negative alongshore pressure gradients, intensified off Pt. Reyes and Pt. Arena by the gradient wind balance, are found south of capes. The negative pressure gradients geostrophically balance onshore flow at depth, and upwelling is strengthened in these locations. North of capes, positive pressure gradients that are primarily in balance with nonlinear advective effects are found. After the winds cease the forced across-shelf circulation weakens, and the resulting unbalanced negative pressure gradients south of the capes accelerate the alongshore currents northward. Processes with similar dynamics are found embedded in the more complex coastal ocean response to observed time varying winds by Gan and Allen [2002].