# gsw_p_from_z

pressure from height (75-term equation)

## Contents

## 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