# gsw_z_from_p

    height from pressure (75-term equation)

## Contents

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

## USAGE:

    z = gsw_z_from_p(p,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)

    Note. Height z is NEGATIVE in the ocean. ie. 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
    height from pressure.

## INPUT:

    p    =  sea pressure                                            [ dbar ]
            ( ie. absolute pressure - 10.1325 dbar )
    lat  =  latitude in decimal degrees north                [ -90 ... +90 ]

    OPTIONAL:
    geo_strf_dyn_height = dynamic height                          [ m2/s^2 ]
    sea_surface_geopotental = geopotential at zero sea pressure  [ m^2/s^2 ]

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

## OUTPUT:

    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.

## EXAMPLE:

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

    z = gsw_z_from_p(p,lat)

    z =

      1.0e+002 *

      -0.099445834469453
      -0.497180897012550
      -1.242726219409978
      -2.484700576548589
      -5.958253480356214
      -9.920919060719987

## AUTHOR:

    Trevor McDougall, Claire Roberts-Thomson & 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