CSIRO Marine Research Ocean Equations Of State for the World's Oceans Software

Algorithms are presented for density, potential temperature, conservative temperature, and the freezing temperature of seawater. The algorithms for potential temperature and density (in terms of potential temperature) are updates to routines recently published by McDougall et al., while the algorithms involving conservative temperature and the freezing temperatures of seawater are new. The McDougall et al. algorithms were based on the thermodynamic potential of Feistel and Hagen; the algorithms in this study are all based on the "new extended Gibbs thermodynamic potential of seawater" of Feistel. The algorithm for the computation of density in terms of salinity, pressure, and conservative temperature produces errors in density and in the corresponding thermal expansion coefficient of the same order as errors for the density equation using potential temperature, both being twice as accurate as the International Equation of State when compared with Feistel's new equation of state. An inverse function relating potential temperature to conservative temperature is also provided. The difference between practical salinity and absolute salinity is discussed, and it is shown that the present practice of essentially ignoring the difference between these two different salinities is unlikely to cause significant errors in ocean models.本文提出了可用于计算海水密度、位势温度（potential temperature）、保守温度（conservative temperature）及海水冻结温度的算法。针对位势温度及以位势温度为自变量的密度的算法，是对McDougall等人近期发表的计算程序的更新；而涉及保守温度与海水冻结温度的算法则为全新研发。McDougall等人的算法基于Feistel与Hagen提出的热力学势；本研究中的全部算法均以Feistel提出的“海水新扩展吉布斯热力学势”为核心理论依据。以盐度、压强与保守温度为变量计算密度的算法，其密度计算误差与对应热膨胀系数的误差量级，与使用位势温度的密度方程的误差量级相当；相较于Feistel提出的新海水状态方程，这两类算法的精度均为国际海水状态方程（International Equation of State）的两倍。本文还提供了可实现位势温度与保守温度相互转换的逆函数。本文探讨了实用盐度（practical salinity）与绝对盐度（absolute salinity）之间的差异，并证实：当前海洋模型中普遍忽略这两类盐度差异的常规做法，不会对模型计算结果造成显著误差。