A NOTE ON THE REPRESENTATION OF STERIC SEA-LEVEL IN MODELS THAT CONSERVE VOLUME RATHER THAN MASS
A NOTE ON THE REPRESENTATION OF STERIC SEA-LEVEL IN MODELS THAT CONSERVE VOLUME RATHER THAN MASS
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DOI：
10.1029/94jc00847
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发表时间：
1994-06-15
影响因子：
3.6
通讯作者：
GREATBATCH, RJ
中科院分区：
文献类型：
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作者：
GREATBATCH, RJ
本文讨论海洋环流模式中空间海平面的表示。当水柱密度的变化意味着水柱的膨胀或收缩时，就会引起空间海平面的变化。模型通常采用Boussinesq近似并保持体积，而不是质量，因此不能正确地表示膨胀或收缩。这意味着，尽管状态方程中包含膨胀/收缩，但模型动力学并不考虑膨胀/收缩。本文研究了控制海平面位移随时间演化的方程。结果表明，需要守恒的质量，而不是体积，引入了一个新的长期这个方程。通过一个简单的算例，说明了新项与表面浮力通量的关系。对新项的均衡反应有两部分。其中一部分由Goldsbrough和Stommel环流组成，在海洋内部，由于水柱的局部膨胀/收缩而导致的涡旋拉伸通过行星涡旋的变化来平衡。另一部分对应于"逆气压计“。其效果是通过一个全球统一但随时间变化的因素来调整海平面，该因素由全球海洋的净扩张/收缩决定。由于这种修正是全局一致的，因此它没有动力学意义。Goldsbrough/Stommel环流和逆气压计的解决方案是从目前制定的模型失踪。这并不代表严重错误。然而，如果与海平面观测值进行比较，则模型计算的海平面应根据全球海洋的净扩张/收缩确定的全球统一的时变因子进行调整。这对于评估海平面因全球变暖而可能上升的情况很重要。
This note discusses the representation of steric sea level in ocean circulation models. Changes in steric sea level are caused when changes in the density of the water column imply an expansion or contraction of the column. Models usually intake the Boussinesq approximation and conserve volume, rather than mass, and so do not properly represent expansion or contraction. This means that although expansion/contraction is included in the equation of state, it is not accounted for by the model dynamics. In this note, we examine the equation governing the time evolution of the sea level displacement. It is shown that requiring conservation of mass, rather than volume, introduces a new term to this equation. A simple example is used to show the relationship of the new term to the surface buoyancy flux. The equilibrium response to the new term has two parts. One part consists of the Goldsbrough and Stommel gyres, for which, in the ocean interior, vortex stretching due to the local expansion/contraction of the water column is balanced by changes in planetary vorticity. The other part corresponds to the ''inverse barometer.'' The effect is to adjust sea level by a globally uniform but time-varying factor, determined by the net expansion/contraction of the global ocean. Since this correction is globally uniform, it has no dynamical significance. Both the Goldsbrough/Stommel gyres and the inverse barometer solution are missing from models as currently formulated. This does not represent a serious error. However, if comparison is made with observations of sea level, model-calculated sea level should be adjusted by a globally uniform, time-varying factor, determined by the net expansion/contraction of the global ocean. This would be important for assessing the likely rise in sea level in response to global warming.