# gsw_ntp_pt_vs_CT_ratio

ratio of gradients of potential temperature and Conservative Temperature in a neutral tangent plane (in a locally-referenced potential density surface) (75-term equation)

## Contents

## USAGE:

ntp_pt_vs_CT_ratio = gsw_ntp_pt_vs_CT_ratio(SA,CT,p)

## DESCRIPTION:

Calculates the ratio of the two-dimensional gradient of potential temperature versus that of Conservative Temperature, CT, along the neutral tangent plane. The potential temperature is the regular one which has a reference sea pressure of 0 dbar. Part of the calculation uses the computationally-efficient 75-term expression for specific volume in terms of SA, CT and p (Roquet et al., 2015).

Note that the 75-term equation has been fitted in a restricted range of parameter space, and is most accurate inside the "oceanographic funnel" described in McDougall et al. (2003). The GSW library function "gsw_infunnel(SA,CT,p)" is avaialble to be used if one wants to test if some of one's data lies outside this "funnel".

Click for a more detailed description of the ratio of gradients of potential temperature and Conservative Temperature in a neutral tangent plane. |

## INPUT:

SA = Absolute Salinity [ g/kg ] CT = Conservative Temperature [ deg C ] p = sea pressure [ dbar ] ( i.e. absolute pressure - 10.1325 dbar )

SA & CT need to have the same dimensions. p may have dimensions 1x1 or Mx1 or 1xN or MxN, where SA & CT are MxN.

## OUTPUT:

ntp_pt_vs_CT_ratio = The ratio of the spatial gradient of potential temperature versus that of Conservative Temperature in the neutral tangent plane (ntp). [ unitless ]

## EXAMPLE:

SA = [34.7118; 34.8915; 35.0256; 34.8472; 34.7366; 34.7324;] CT = [28.8099; 28.4392; 22.7862; 10.2262; 6.8272; 4.3236;] p = [ 10; 50; 125; 250; 600; 1000;]

ntp_pt_vs_CT_ratio = gsw_ntp_pt_vs_CT_ratio(SA,CT,p)

ntp_pt_vs_CT_ratio =

1.016134758732110 1.016088712417197 1.011784401675508 1.004314345783137 1.003011679980744 1.002334099137641

## AUTHOR:

Trevor McDougall and Paul Barker [ help@teos-10.org ]

## VERSION NUMBER:

3.05 (16th February, 2015)

## REFERENCES:

IOC, SCOR and IAPSO, 2010: The international thermodynamic equation of seawater - 2010: Calculation and use of thermodynamic properties. Intergovernmental Oceanographic Commission, Manuals and Guides No. 56, UNESCO (English), 196 pp. Available from the TEOS-10 web site. See Eqn. (A.14.5) of this TEOS-10 Manual.

McDougall, T.J., D.R. Jackett, D.G. Wright and R. Feistel, 2003: Accurate and computationally efficient algorithms for potential temperature and density of seawater. J. Atmosph. Ocean. Tech., 20, pp. 730-741.

Roquet, F., G. Madec, T.J. McDougall, P.M. Barker, 2015: Accurate polynomial expressions for the density and specifc volume of seawater using the TEOS-10 standard. Ocean Modelling.

This software is available from http://www.TEOS-10.org