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首页> 外文期刊>Journal of Physical Oceanography >Energy Conversion, Mixing Energy, and Neutral Surfaces with a Nonlinear Equation of State
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Energy Conversion, Mixing Energy, and Neutral Surfaces with a Nonlinear Equation of State

机译：能量转换，混合能量和具有非线性状态方程的中性表面

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A local neutral plane is defined so that a water parcel that is displaced adiabatically a small distance along the plane continues to have the same density as the surrounding water. Since such a displacement does not change the density field or the gravitational potential energy, it is generally assumed that it does not produce a restoring buoyancy force. However, it is here shown that because of the nonlinear character of the equation of state (in particular the thermobaric effect) such a neutral displacement is accompanied by a conversion between internal energy E and gravitational potential energy U, and an equal conversion between U and kinetic energy K. While there is thus no net change of U, K does change. This implies that a force is in fact required for the displacement. It is further shown that displacements that are orthogonal to a vector P do not induce conversion between U and K, and therefore do not require a force. Analogously to neutral surfaces, which are defined to be approximately orthogonal to the dianeutral vector N, one may define "P surfaces" to be approximately orthogonal to P. These P surfaces are intermediate between neutral surfaces and surfaces of constant σ_0 (potential density reference to the surface). If the equation of state is linear, there exists a well-known expression for the mixing energy in terms of the diapycnal flow. This expression is here generalized for a general nonlinear equation of state. The generalized expression involves the velocity component along P. Since P is not orthogonal to neutral surfaces, this means that stationary flow along neutral surfaces in general requires mixing energy.
机译：定义了局部中性平面，以使沿该平面绝热地移动了一小段距离的水块继续具有与周围水相同的密度。由于这种位移不会改变密度场或重力势能，因此通常认为它不会产生恢复浮力。但是，这里显示出，由于状态方程的非线性特性（特别是热压效应），这种中性位移伴随有内部能量E和重力势能U之间的转换，以及U和E之间的相等转换。动能K。因此，虽然U没有净变化，但K确实发生了变化。这实际上意味着位移需要力。进一步示出，正交于向量P的位移不会引起U和K之间的转换，因此不需要力。类似于中性表面，将其定义为与正交向量N大致正交，可以将“ P个表面”定义为与P近似正交。这些P个表面介于中性表面和常数σ_0（介于表面）。如果状态方程是线性的，则存在关于混合能量的以径向流动为单位的公知表达式。该表达式在这里针对一般的非线性状态方程进行了概括。广义表达式包含沿P的速度分量。由于P与中性表面不正交，因此这意味着沿中性表面的平稳流动通常需要混合能。

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  • 来源
    《Journal of Physical Oceanography》 |2011年第1期|p.28-41|共14页
  • 作者

    Jonas Nycander;

  • 作者单位

    Dept. of Mete-orology, University of Stockholm, Stockholm 106 91, Sweden;

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