Numerical implementation and oceanographic application of the thermodynamic potentials of water, vapour, ice, seawater and air – Part 2: The library routines

Abstract

Abstract. The SCOR/IAPSO1 Working Group 127 on Thermodynamics and Equation of State of Seawater has prepared recommendations for new methods and algorithms for numerical estimation of the thermophysical properties of seawater. As an outcome of this work, a new International Thermodynamic Equation of Seawater (TEOS-10) was endorsed by IOC/UNESCO2 in June 2009 as the official replacement and extension of the 1980 International Equation of State, EOS-80. As part of this new standard a source code package has been prepared that is now made freely available to users via the World Wide Web. This package includes two libraries referred to as the SIA (Sea-Ice-Air) library and the GSW (Gibbs SeaWater) library. Information on the GSW library may be found on the TEOS-10 web site (http://www.TEOS-10.org). This publication provides an introduction to the SIA library which contains routines to calculate various thermodynamic properties as discussed in the companion paper. The SIA library is very comprehensive, including routines to deal with fluid water, ice, seawater and humid air as well as equilibrium states involving various combinations of these, with equivalent code developed in different languages. The code is hierachically structured in modules that support (i) almost unlimited extension with respect to additional properties or relations, (ii) an extraction of self-contained sub-libraries, (iii) separate updating of the empirical thermodynamic potentials, and (iv) code verification on different platforms and between different languages. Error trapping is implemented to identify when one or more of the primary routines are accessed significantly beyond their established range of validity. The initial version of the SIA library is available in Visual Basic and FORTRAN as a supplement to this publication and updates will be maintained on the TEOS-10 web site. 1 SCOR/IAPSO: Scientific Committee on Oceanic Research/International Association for the Physical Sciences of the Oceans 2 IOC/UNESCO: Intergovernmental Oceanographic Commission/United Nations Educational, Scientific and Cultural Organization

Thermodynamic properties of sea air

“…That is, new functions based on the fundamental thermodynamic relations can be introduced into user libraries (e.g., Feistel et al, 2009;Wright et al, 2009) and/or new or extended versions of the empirically determined thermodynamic potentials can be introduced without directly affecting the other part. All that is required is that a standard interface be established to communicate information between the two parts.…”

“…Based on functions available from the literature as repeated in detail in the appendix, a new seawater library Wright et al, 2009) has currently been developed as source code in Fortran and Visual Basic, with later versions planned also in MatLab and C/C++, and will offer easy Table A1. Chemical composition of sea salt (Millero et al, 2008 (9) Sea salt 1.000 0000 1.000 0000 31.404 (2) access to sea-air as well as fluid water, ice and seawater properties.…”

“…of seawater (IAPWS, 2008a;Feistel, 2008a;Feistel et al, 2009;Wright et al, 2009) consist of a pure-water part, g W , available from the Helmholtz function f W (T , ρ) given by the IAPWS-95 formulation, and a saline addition, g S , accounting for the solute regarded as sea salt. Here, S A = m S / m W + m S is the absolute salinity (Millero et al, 2008), expressed by the mass, m S , of salt dissolved in a mass of liquid water, m W .…”

“…Combined, these four potentials permit the computation of thermodynamic properties of the atmosphere, the ocean, clouds, ice and lakes in a comprehensive and consistent manner, valid over wide ranges in temperature, pressure and concentrations, from polar cirrus clouds at high altitudes to saline estuaries in the tropics, with the highest accuracy presently available. Rather than being a mere theoretical exercise, these four independent functions and numerous properties derived thereof are available from a numerical source-code library which has currently been developed, supporting the implementation of the intended new oceanographic TEOS-10 standard Wright et al, 2009). The library will be available in Fortran and Visual Basic/Excel for easy use on various platforms.…”

“…The time it takes to determine tailored formulae or to compute and store tabulated values in look-up tables is irrelevant for their later usage. The sea-air functions implemented in the library Wright et al, 2009) permit the computation of look-up tables for practically any desired combination of input and output properties, since the thermodynamic potentials provide a complete description. Real-time models 96 R. Feistel et al: Thermodynamic properties of sea air require the highest computation speeds; so, we believe that our equations may well feed such models with the most accurate properties available.…”