# gsw_enthalpy_diff

    difference of enthalpy between two pressures (48-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 48-term expression for
    density in terms of SA, CT and p (McDougall et al., 2011).  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 48-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. (2011).  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 *

       9.784175745249133
       9.780190029261341
       9.759582348180077
       9.727549624783435
       9.708223563805783
       9.687874865406878

## AUTHOR:

    Trevor McDougall & Claire Roberts-Thomson.          [ help@teos-10.org ]

## VERSION NUMBER:

    3.01 (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 Eqns. (3.32.2) and (A.30.6) of this TEOS-10 Manual.

    McDougall T.J., P.M. Barker, R. Feistel and D.R. Jackett, 2011:  A
     computationally efficient 48-term expression for the density of
     seawater in terms of Conservative Temperature, and related properties
     of seawater.  To be submitted to Ocean Science Discussions.

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