The Materiality and Neutrality of Neutral Density and Orthobaric Density
The Materiality and Neutrality of Neutral Density and Orthobaric Density
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中性密度和正压密度的物质性和中性
DOI：
10.1175/2009jpo4042.1
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发表时间：
2009
影响因子：
3.5
通讯作者：
S. Springer
中科院分区：
文献类型：
--
作者：
R. D. Szoeke;S. Springer
通过对大西洋暖球水团性质的简单理想化，计算和比较了中性密度和几种正压密度的重要性和中立性。物质性是物质导数的值，表示为准垂直速度，跟随每个变量的运动：零物质性表示完美守恒。中立性是各变量等等值面的倾角与中性面的倾角之间的差异。水样中性密度的重要性和中性性是由以下因素组成的：(I)样品的温度和盐度与当地参考u - S关系的密切程度，（II）参考u - S关系的空间变化，（III）潜在参考中性密度表面的中性性，以及（IV）热量和盐度的不可逆交换。II型贡献占主导地位，但在以前的中性密度特性评估中被忽视。使用空间均匀的u - S关系定义的简单正压密度表面的物质性和中立性具有类似于类型I和IV的贡献，但缺乏类型II或III的任何贡献。扩展正压密度的概念以允许u - S关系的空间变化，减少了I型贡献，但II型贡献的出现抵消了这种影响。扩展正压密度的离散类比，基于区域间边界匹配的区域平均u - S关系，揭示了扩展正压密度与实际中性密度之间的密切相似。在物质性或中立性方面，中性密度并不优于简单的正压密度。
The materiality and neutrality of neutral density and several forms of orthobaric density are calculated and compared using a simple idealization of the warm-sphere water mass properties of the Atlantic Ocean. Materiality is the value of the material derivative, expressed as a quasi-vertical velocity, following the motion of each of the variables: zero materiality denotes perfect conservation. Neutrality is the difference between the dip in the isopleth surfaces of the respective variables and the dip in the neutral planes. The materiality and neutrality of the neutral density of a water sample are composed of contributions from the following: (I) how closely the sample’s temperature and salinity lie in relation to the local reference u‐S relation, (II) the spatial variation of the reference u‐S relation, (III) the neutrality of the underlying reference neutral density surfaces, and (IV) irreversible exchanges of heat and salinity. Type II contributions dominate but have been neglected in previous assessments of neutral density properties. The materiality and neutrality of surfaces of simple orthobaric density, defined using a spatially uniform u‐S relation, have contributions analogous to types I and IV, but lack any of types II or III. Extending the concept of orthobaric density to permit spatial variation of the u‐S relation diminishes the type I contributions, but the effect is counterbalanced by the emergence of type II contributions. Discrete analogs of extended orthobaric density, based on regionally averaged u‐S relations matched at interregional boundaries, reveal a close analogy between the extended orthobaric density and the practical neutral density. Neutral density is not superior, even to simple orthobaric density, in terms of materiality or neutrality.