# gsw_geo_strf_Cunningham

    Cunningham geostrophic streamfunction

## Contents

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

## USAGE:

    [geo_strf_Cunningham, in_funnel] = gsw_geo_strf_Cunningham(SA,CT,p,interp_style)

## DESCRIPTION:

    Calculates the Cunningham geostrophic streamfunction (see Eqn. (3.29.2)
    of IOC et al. (2010)).  This is the geostrophic streamfunction for the
    difference between the horizontal velocity at the pressure concerned,
    p, and the horizontal velocity at the sea surface.  This function
    calculates specific volume anomaly using the computationally efficient
    25-term expression for specific volume of McDougall et al. (2010).
    Under the default setting, this function evaluates the pressure integral
    of specific volume using SA and CT “interploted” with respect to pressure
    using a scheme based on the method of Reiniger and Ross (1968).  Our
    method uses a weighted mean of (i) values obtained from linear
    interpolation of the two nearest data points, and (ii) a linear
    extrapolation of the pairs of data above and below. This "curve fitting"
    method resembles the use of cubic splines.  If the option “linear” is
    chosen, the function interpolates Absolute Salinity and Conservative
    Temperature linearly with presure in the vertical between “bottles”.

    Click for a more detailed description of the Cunningham
    streamfunction.

## INPUT:

    SA   =  Absolute Salinity                                       [ g/kg ]
    CT   =  Conservative Temperature                               [ deg C ]
    p    =  sea pressure                                            [ dbar ]
           ( ie. absolute pressure - 10.1325 dbar )

    OPTIONAL:
    interp_style = interpolation technique.
                 = if nothing is entered the programme defaults to "curved"
                   interpolation between bottles in the vertical.
                 = if "linear" or "lin" is entered then the programme
                   interpolates linearly between bottles in the
                   vertical.

    SA & CT need to have the same dimensions.
    p may have dimensions Mx1 or 1xN or MxN, where SA & CT are MxN.

## OUTPUT:

    geo_strf_Cunningham = Cunningham geostrophic streamfunction  [ m^2/s^2 ]

    in_funnel           = 0, if SA, CT and p are outside the "funnel"
                        = 1, if SA, CT and p are inside the "funnel"
    Note. The term "funnel" describes the range of SA, CT and p over which
      the error in the fit of the computationally-efficient 25-term
      expression for density was calculated (McDougall et al., 2010).

## 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;]
    p =  [     10;      50;     125;     250;     600;    1000;]

    [geo_strf_Cunningham, in_funnel] = gsw_geo_strf_Cunningham(SA,CT,p)

    geo_strf_Cunningham =             in_funnel =

       0.6007                             1
      -0.0151                             1
      -1.6280                             1
      -6.5022                             1
      -8.3101                             1
     -10.7625                             1

## AUTHOR:

     Trevor McDougall and Paul Barker [ help_gsw@csiro.au ]

## VERSION NUMBER:

    2.0 (26th August, 2010)

## REFERENCES:

    Cunningham, S.A., 2000: Circulation and volume flux of the North
     Atlantic using syoptic hydrographic data in a Bernoulli inverse.
     J. Marine Res., 58, 1-35.

    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 section 3.29 of this TEOS-10 Manual.

    McDougall T.J., D.R. Jackett, P.M. Barker, C. Roberts-Thomson, R.
     Feistel and R.W. Hallberg, 2010:  A computationally efficient 25-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