# gsw_ntp_pt_vs_CT_ratio_CT25

    ratio of gradients of potential temperature
    and Conservative Temperature in a neutral
    tangent plane (in a locally-referenced
    potential density surface) (25-term equation)

## Contents

- USAGE:
- DESCRIPTION:
- INPUT:
- OUTPUT:
- EXAMPLE:
- AUTHOR:
- VERSION NUMBER:
- REFERENCES:

## USAGE:

    [ntp_pt_vs_CT_ratio_CT25, in_funnel] = gsw_ntp_pt_vs_CT_ratio_CT25(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 25-term expression for density in
    terms of SA, CT and p (McDougall et al., 2010).

    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 ]
            (ie. 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_CT25  =  The ratio of the spatial gradient of
                                potential temperature versus that of
                                Conservative Temperature in the
                                neutral tangent plane (ntp).    [ unitless ]
    in_funnel  =  0, if SA, CT and p are outside the "funnel"
               =  1, if SA, CT and p are inside the "funnel"
    Note. The term "funnel" describes the range of SA, CT and p over which
      the error in the fit of the computationally-efficient 25-term
      expression for density was calculated (McDougall et al., 2010).

## 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_CT25, in_funnel] = ...
                         gsw_ntp_pt_vs_CT_ratio_CT25(SA,CT,p)

    ntp_pt_vs_CT25_ratio =             in_funnel =

     1.016122079370071                   1
     1.016078060102738                   1
     1.011790779852534                   1
     1.004313933279649                   1
     1.003007924869312                   1
     1.002330826430900                   1

## AUTHOR:

    Trevor McDougall and Paul Barker    [ gsw_help@csiro.au ]

## VERSION NUMBER:

    2.0 (26th August, 2010)

## 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, P. M. Barker, C. Roberts-Thomson, R.
     Feistel and R. W. Hallberg, 2010:  A computationally efficient 25-term
     expression for the density of seawater in terms of Conservative
     Temperature, and related properties of seawater.  To be submitted
     to Ocean Science Discussions.

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