A new set of approximations to the standard TEOS-10 equation of state has recently been proposed. These follow a polynomial form, making it computationally efficient for use in numerical ocean models. Two versions are provided, the first polyTEOS10_bsq being a fit of density for Boussinesq ocean models, and the second polyTEOS10_55t fitting specific volume which is more suitable for compressible models.
Both versions are given as the sum of a vertical reference profile (6th-order polynomial) and an anomaly (52-term polynomial, cubic in pressure), with relative errors of 0.1% on the thermal expansion coefficients.
A 75-term polynomial expression polyTEOS10_75t is also presented for computing specific volume, with a better accuracy than the existing TEOS-10 48-term rational approximation, especially regarding the sound speed. This version is now used (since 2015) as the standard approximation of the TEOS-10 equation of state.
Finally, a stiffened version polyTEOS10_stif of the equation of state is also proposed.
More details on these approximations of the TEOS-10 equation of state are available in Roquet et al. (2016).
Reference: Roquet, F., Madec, G., McDougall, T. J., and Barker, P. M., 2015. Accurate polynomial expressions for the density and specific volume of seawater using the TEOS-10 standard. Ocean Modelling, 90:29-43.