Energy fluxes and cascades in models of ocean circulation

海洋环流模型中的能量通量和级联

• 批准号: 155049-2012
• 负责人: Straub, David
• 金额: $ 2.77万
• 依托单位: McGill University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2012
• 资助国家: 加拿大
• 起止时间: 2012-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=507820
• 关键词: Energy; fluxes; cascades; models; ocean

Understanding ocean circulation involves understanding how mechanical energy is transferred from the basin scale where it is added by the winds to the centimetre scale where it is converted to heat. Ocean currents and eddies are in approximately geostrophic balance (Coriolis and horizontal pressure gradient forces) on length scales down to 10km. How energy is transferred from the basin scale to the ocean mesoscale (10-50km) is reasonably well understood, although part of this proposal corrects some misconceptions relating to this process. A bigger problem is getting energy from the mesoscale to the smaller submesoscale. The mesoscale is characterized by geostrophic turbulence which, unlike 3d turbulence, transfers energy in the inverse sense: from small to large scales. Dissipation then requires a transfer of energy from the nearly-geostrophic circulation to ageostrophic modes such as inertial oscillations. Much work suggests these transfers to be weak in the interior of the water column. Observations, however, show a rich field of near-inertial motion (frequencies close to the Coriolis frequency) super-imposed on the geostrophic flow. These are forced in large part by high frequency events (stroms, tides, etc) that are often ignored in theoretical studies. In other words, the background level of near-inertial motion in the ocean is considerably higher than it is in most studies aimed at quantifying these sorts of energy transfers. High frequency forcing increases the background level of the near-inertial energy. Our basic thesis is that this can significantly enhance the geostrophic to ageostrophic energy transfer mechanism and - even where it does not - will affect the vertical velocity field (and hence transport of tracers). We consider various forcing mechanisms to excite the unbalanced motion; for example, a sea surface temperature dependence in the wind stress divergence which may add significant ageostrophic motion to strong ocean currents (where geostrophic to ageostrophic transfers more readily occur). Finally, because much of the wind energy input occurs over the Southern Ocean, some of our work will relate to an understanding of the Antarctic Circumpolar Current.

了解海洋环流包括了解机械能如何从盆地尺度(风将其添加到厘米尺度)转移到厘米尺度(将其转化为热量)。洋流和涡旋在长度尺度上大致处于地转平衡(科里奥利力和水平气压梯度力)，直至10公里。能量如何从盆地尺度转移到海洋中尺度(10-50公里)是相当清楚的，尽管这一提议的一部分纠正了与这一过程有关的一些误解。一个更大的问题是将能量从中尺度转移到更小的亚中尺度。中尺度以地转湍流为特征，与3D湍流不同，它以相反的意义传递能量：从小尺度到大尺度。消散则需要能量从近地转环流转移到非地转模式，如惯性振荡。许多研究表明，这些迁移在水柱内部很弱。然而，观测显示了叠加在地转流上的丰富的近惯性运动(频率接近科里奥利频率)。这在很大程度上是由高频事件(闪电、潮汐等)造成的，这些事件在理论研究中往往被忽视。换句话说，海洋中近惯性运动的背景水平比大多数旨在量化这种能量转移的研究中的水平要高得多。高频强迫增加了近惯性能量的背景能级。我们的基本论点是，这可以显著地增强地转到非地转的能量传递机制，并且--即使它不会--将影响垂直速度场(从而影响示踪物的传输)。我们考虑了激发不平衡运动的各种强迫机制；例如，风应力散度对海表面温度的依赖，这可能会给强洋流增加显著的非地转运动(在那里更容易发生地转到非地转的转换)。最后，由于大部分风能输入发生在南大洋上，我们的一些工作将与理解南极绕极洋流有关。