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首页> 外文期刊>Journal of Physical Oceanography >Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders
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Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

机译：海洋亚中尺度运动：滑翔机混合层不稳定性的整个季节周期

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摘要

The importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km(2) region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (~20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September-November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December-March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the open-ocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.
机译：在强而持久的前沿地区，例如黑潮和海湾流域，亚中尺度的不稳定性，特别是混合层斜压不稳定性和对称不稳定性对上层海洋混合和高能的重要性已得到充分证明。投入较少的精力用于研究远洋中的亚中尺度水流，远离长期的，平均的地转锋面，这是全球大部分海洋的特征。这项研究提出了由海洋滑翔机收集的长达一年的近地表浮力梯度，潜在涡度和不稳定性特征的亚中尺度尺度的时间序列，可提供整个全年周期内开放海洋亚中尺度尺度动力学的见识。滑翔机连续采样了亚热带东北大西洋一个225 km（2）的区域，沿292个短（〜20 km）水文剖面测量了温度，盐度和压力。滑翔机的观测结果表明近地表分层有一个季节性周期。在整个秋季（9月至11月），混合层加深，主要是由于重力不稳定性，表明表面冷却主导了亚中尺度的再成矿过程。在冬季（12月至3月），混合层深度变化更大，平衡的理查森数估计值（测量横向和垂直浮力梯度的相对重要性）描述了有利于对称不稳定的条件。与表面加热和冷却相比，混合层不稳定性对混合层再平衡的重要性表明，亚中尺度过程可以使等效热通量的符号逆转，冬季最多可达25％。这些结果表明，开放海洋混合层具有各种强迫和非强迫的不稳定性，这些不稳定性在冬季更为普遍，并强调整个海洋都需要对亚中尺度过程进行精确的参数化。

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