# Gamma Global Polynomial (γGP)

These pages contain oceanographic software based on seawater equations of state that predate TEOS-10 (such as EOS-80 and JMFWG-06).

# Reference

Serazin, G., T.J. McDougall and P.M. Barker (2012) An approximate Neutral Density variable for the world's oceans.
To be submitted to *J. Atmos. Ocean. Tech.*

# Abstract

Transport of heat, salt and other tracers in the ocean occurs principally along neutral surfaces. Due to the significant differences in mixing intensities between the exchanges that occur along and those that occur through these surfaces, it is crucial to be able to accurately determine neutral surfaces in order to describe flows inside the ocean. Because neutral surfaces are not mathematically well defined, several density variables have been introduced in order to approximate them. Potential density referenced to 2000 db is typically used in oceans models because it is fast compute. However, the results are close to being neutral only around the reference pressure. The two Neutral Density functions γn and gamma_i currently provide the best approximation of neutral surfaces unfortunately they are not practical solutions for use in ocean models because they are very computationally intensive. Hence, this project aims to build an approximate form of Neutral Density, gamma_GP, which is designed to replace the current variable sigma_2 in ocean models. The world's oceans were decomposed into segments that covered each of the major oceanic basins. This allowed for accurate polynomial functions, gamma_poly, to be fitted to a Neutral Density labelled version of the WOCE climatology. The global polynomial gamma_GP is a result of combining each of the gamma_poly functions. The polynomials have been built in terms of Practical Salinity and potential temperature to be able be applied in current ocean models. The gamma_poly polynomials give 30 % of improvement compared to sigma_2 in the amount of fictitious dyapicnal diffusivity on the Southern Ocean and at least 40 % on the other ocean basins. Performed on a snapshot of the ocean model MOM4, the global polynomial gamma_GP has a 45 % reduction in fictitious dyapicnal diffusivity when compared with those from sigma_2.

# Code and documentation

*Note that this is a beta release*

# Corresponding author address:

Email: god@teos-10.org