Revisiting Near-Inertial Wind Work: Slab Models, Relative Stress, and Mixed Layer Deepening
Revisiting Near-Inertial Wind Work: Slab Models, Relative Stress, and Mixed Layer Deepening
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DOI：
10.1175/jpo-d-20-0105.1
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发表时间：
2020-11-01
影响因子：
3.5
通讯作者：
Alford, Matthew H.
中科院分区：
文献类型：
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作者：
Alford, Matthew H.
通过使用 Pollard-Rhines-Thompson 理论、Price-Weller-Pinkel (PWP) 混合层模型以及 Crawford 和 Large 的共振力 KPP 模拟，重新审视了风力产生的近惯性波。 Argo 混合层气候学和 0.6 度 MERRA-2 再分析风用于计算全球总数并探索假设。首先，当混合层相对于缩放比例 H* [u*/(Nf)(1/2) 较浅时，平板模型会高估风功 2-4 倍，但对于较深的混合层却很准确，与 PWP 相比，将全球总量高估了 1.23 +/- 0.03 倍。利用相对于洋流的风应力进一步将风功进一步减少 13 +/- 0.3%，全球总风功为 0.26 TW。其次，检查了由于风驱动混合层加深而导致的 Delta PE 势能增加，并与根据 Argo 和 ERA-Interim 热通量气候学计算出的 Delta PE 进行了比较。 Argo 衍生的 Delta PE 与冷却密切相关，证实冷却决定了混合层深度的季节周期，并为混合层底部对流浮力通量的观测估计提供了新的约束。在局部地区和秋季，风力加深的重要性与降温相当。在全球范围内，风力驱动的 Delta PE 约占风功的 11%，这意味着超过 50% 的风功转化为湍流，因此不会传播惯性运动。这种“改进的风功”的比例以两种方式进行了不完美的估计，但我们得出的结论是，需要对混合层和过渡层物理进行更多研究。因此，可用于传播近惯性波的功率仍然不确定，但似乎比之前认为的要低。
The wind generation of near-inertial waves is revisited through use of the Pollard-Rhines-Thompson theory, the Price-Weller-Pinkel (PWP) mixed layer model, and KPP simulations of resonant forcing by Crawford and Large. An Argo mixed layer climatology and 0.6 degrees MERRA-2 reanalysis winds are used to compute global totals and explore hypotheses. First, slab models overestimate wind work by factors of 2-4 when the mixed layer is shallow relative to the scaling H* [u*/(Nf)(1/2), but are accurate for deeper mixed layers, giving overestimation of global totals by a factor of 1.23 +/- 0.03 compared to PWP. Using wind stress relative to the ocean currents further reduces the wind work by an additional 13 +/- 0.3%, for a global total wind work of 0.26 TW. Second, the potential energy increase Delta PE due to wind-driven mixed layer deepening is examined and compared to Delta PE computed from Argo and ERA-Interim heat flux climatology. Argo-derived Delta PE closely matches cooling, confirming that cooling sets the seasonal cycle of mixed layer depth and providing a new constraint on observational estimates of convective buoyancy flux at the mixed layer base. Locally and in fall, wind-driven deepening is comparable in importance to cooling. Globally, wind-driven Delta PE is about 11% of wind work, implying that >50% of wind work goes to turbulence and thus not into propagating inertial motions. The fraction into this "modified wind work'' is imperfectly estimated in two ways, but we conclude that more research is needed into mixed layer and transition-layer physics. The power available for propagating near-inertial waves is therefore still uncertain, but appears lower than previously thought.