# gsw_p_from_z

`pressure from height (75-term equation)`

## 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`