# gsw_z_from_p

`height from pressure (75-term equation)`

## 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`