gsw_sigma4

potential density anomaly with reference pressure
of 4000 dbar, this being this particular potential
density minus 1000 kg/m^3 (75-term equation)

Contents

USAGE:

sigma4 = gsw_sigma4(SA,CT)

DESCRIPTION:

Calculates potential density anomaly with reference pressure of 4000 
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".
TEOS-10 
Click for a more detailed description of potential
density anomaly with p_ref of 4000 dbar (sigma_1).

INPUT:

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

OUTPUT:

sigma4  =  potential density anomaly with                     [ kg/m^3 ]
           respect to a reference pressure of 4000 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;]
sigma4 = gsw_sigma4(SA,CT)
sigma4 =
  37.900374609834898
  38.166979617032439
  40.280876075282549
  43.896091033421953
  44.631677245327637
  45.171817312020039

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