# gsw_enthalpy_diff

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

## 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`