# gsw_sigma3

```potential density anomaly with reference pressure
of 3000 dbar, this being this particular potential
density minus 1000 kg/m^3 (75-term equation)```

## USAGE:

`sigma3 = gsw_sigma3(SA,CT)`

## DESCRIPTION:

```Calculates potential density anomaly with reference pressure of 3000
dbar, this being this particular potential density minus 1000 kg/m^3.
This function has inputs of Absolute Salinity and Conservative
Temperature.  This function 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 potential density anomaly with p_ref of 3000 dbar (sigma_1).```

## INPUT:

```SA  =  Absolute Salinity                                        [ g/kg ]
CT  =  Conservative Temperature                                [ deg C ]```
`SA & CT need to have the same dimensions.`

## OUTPUT:

```sigma3  =  potential density anomaly with                     [ kg/m^3 ]
respect to a reference pressure of 3000 dbar,
that is, this potential density - 1000 kg/m^3.```

## 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;]```
`sigma3 = gsw_sigma3(SA,CT)`
`sigma3 =`
```  34.003747849903675
34.267409891564057
36.316415829697917
39.732367693977039
40.397934186745033
40.881795690566832```

## AUTHOR:

`Trevor McDougall & 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.30.1) 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`