# gsw_p_from_z

    pressure from height (75-term equation)

## Contents

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

## USAGE:

    p = gsw_p_from_z(z,lat,{geo_strf_dyn_height},{sea_surface_geopotental})

## DESCRIPTION:

    Calculates sea pressure from height using computationally-efficient
    75-term expression for specific volume (Roquet et al., 2015).  Dynamic
    height anomaly, geo_strf_dyn_height, if provided, must be computed with
    its p_ref = 0 (the surface). Also if provided, sea_surface_geopotental
    is the geopotential at zero sea pressure. This function solves
    Eqn.(3.32.3) of IOC et al. (2010) iteratively for p.

    Note. Height (z) is NEGATIVE in the ocean.  Depth is -z.
          Depth is not used in the GSW computer software library.

    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 calculating
    pressure from height.

## INPUT:

    z   =  height                                                      [ m ]
     Note. At sea level z = 0, and since z (HEIGHT) is defined
       to be positive upwards, it follows that while z is
       positive in the atmosphere, it is NEGATIVE in the ocean.
    lat =  latitude in decimal degrees north                 [ -90 ... +90 ]

    OPTIONAL:
    geo_strf_dyn_height = dynamic height anomaly                 [ m^2/s^2 ]
      Note that the reference pressure, p_ref, of geo_strf_dyn_height must
       be zero (0) dbar.

    lat may have dimensions 1x1 or Mx1 or 1xN or MxN, where z is MxN.
    geo_strf_dyn_height and geo_strf_dyn_height, if provided, must have
    dimensions MxN, which are the same as z.

## OUTPUT:

     p  =  sea pressure                                             [ dbar ]
           ( i.e. absolute pressure - 10.1325 dbar )

## EXAMPLE:

    z   =  [    -10;     -50;    -125;    -250;    -600;   -1000;]
    lat = 4;

    p = gsw_p_from_z(z,lat)

    p =
     1.0e+003 *

       0.010055726724518
       0.050283543374874
       0.125731858435610
       0.251540299593468
       0.604210012340727
       1.007990337692001

## AUTHOR:

    Trevor McDougall, Claire Roberts-Thomson 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.

    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.

    Moritz, 2000: Goedetic reference system 1980. J. Geodesy, 74, 128-133.

    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.

    Saunders, P. M., 1981: Practical conversion of pressure to depth.
     Journal of Physical Oceanography, 11, 573-574.

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