# gsw_enthalpy_diff

    difference of enthalpy between two pressures (75-term equation)

## Contents

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

## USAGE:

    enthalpy_diff = gsw_enthalpy_diff(SA,CT,p_shallow,p_deep)

## DESCRIPTION:

    Calculates the difference of the specific enthalpy of seawater between
    two different pressures, p_deep (the deeper pressure) and p_shallow
    (the shallower pressure), at the same values of SA and CT.  This
    function uses the computationally-efficient 75-term expression for
    specific volume in terms of SA, CT and p (Roquet et al., 2015).  The
    output (enthalpy_diff) is the specific enthalpy evaluated at
    (SA, CT, p_deep) minus the specific enthalpy at (SA, CT, p_shallow).

    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 difference
    of enthalpy between two pressures

## INPUT:

    SA         =  Absolute Salinity                                 [ g/kg ]
    CT         =  Conservative Temperature                         [ deg C ]
    p_shallow  =  upper sea pressure                                [ dbar ]
                  (ie. shallower absolute pressure - 10.1325 dbar)
    p_deep     =  lower sea pressure                                [ dbar ]
                  (ie. deeper absolute pressure - 10.1325 dbar)

    p_shallow and p_deep may have dimensions Mx1 or 1xN or MxN,
    where SA and CT are MxN.

## OUTPUT:

    enthalpy_diff  =  difference of specific enthalpy               [ J/kg ]
                      (deep minus shallow)

## EXAMPLE:

    SA        =  [34.7118; 34.8915; 35.0256; 34.8472; 34.7366; 34.7324;]
    CT         =  [28.7856; 28.4329; 22.8103; 10.2600;  6.8863;  4.4036;]
    p_shallow =  [     10;      50;     125;     250;     600;    1000;]
    p_deep    =  [    110;     150;     225;     350;     700;    1100;]

    enthalpy_diff = gsw_enthalpy_diff(SA,CT,p_shallow,p_deep)

    enthalpy_diff =

    1.0e+002 *

       9.784180644568052
       9.780195056105020
       9.759587700515114
       9.727552719534447
       9.708223170174454
       9.687871289079633

## 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 Eqns. (3.32.2) and (A.30.6) 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.

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