The seawater package

Introduction

The seawater module provides basic functions in Python for physical properties of sea water. The scope is similar to the MATLAB toolboxes SEAWATER from CSIRO and parts of OCEANS from Woods Hole Institute.

Most of the formulas used are taken from Unesco's joint panel on oceanographic tables and standards, UNESCO 1981 and UNESCO 1983.

The present version is 1.2, released 22 January 2015 This is an minor update from version 1.1 from 2004. It is now compatible with python 3 and 2.7.

With the new Gibbs function based equation of state TEOS-10 this seawater package is becoming obsolete. It is retained here under the MIT-license for backwards compability. Filipe Fernandes is leading the python implentation of the new equation of state in python, python-gsw.

User documentation

The functions are mainly polynomials, with an occasional fractional exponent. The functions can therefore be used traditionally without NumPy to compute a single value. With NumPy the functions act like "ufuncs" in the NumPy sence. This means that they can take array arguments and return an array of the same shape.

Public functions:

Density related
  dens(S,T,P)           Density of sea water              kg/m**3
  svan(S,T,P)           Specific volume anomaly           m**3/kg
  sigma(S,T,P)          Density anomaly                   kg/m**3
  drhodt(S,T,P)         Temperature derivative of density kg/(K*m**3)
  alpha(S,T,P)          Thermal expansion coefficient     1/K
  drhods(S,T,P)         Salinity derivative of density    kg/m**3
  beta(S,T,P)           Salinity expansion coefficient

Salinity related
  salt(R,T,P)           Salinity
  cond(S,T,P)           Conductivity ratio

Heat related
  heatcap(S,T,P)        Heat capacity                     J/(kg*K)
  adtgrad(S,T,P)        Adiabatic lapse rate              K/dbar
  temppot(S,T,P,Pref)   Potential temperature             °C
  temppot0(S,T,P)       Potential temperature             °C

Miscellaneous
  freezept(S,P)         Freezing point                    °C
  soundvel(S,T,P)       Sound velocity                    m/s
  depth(P,lat)          Depth                             m

Arguments:
  S                     Salinity
  T                     Temperature                       °C
  P                     Pressure                          dbar
  R                     Conductivity ratio
  Pref                  Reference pressure                dbar
  lat                   Latitude                          deg

Test scripts

The test directory contains several test scripts. The script test.py tests some standard values in the UNESCO 1983 report. The script testwater.py prints out part of table A3.1 in the book by Gill (1982). To recreate the potential temperature values the alternative function temppot0, implementing an algorithm from Bryden (1973), is used.

The scripts testdens, testsalt, testheat, and testmisc computes and prints tables from the UNESCO 1983 report.

Install

The seawater package is written in pure Python and should work on any system. NumPy is not necessary, but highly recommended. To install the package, use the commands:

python setup.py build python setup.py install

(the install commmand may need root access).

References

Bryden, 1973 New polynomials for thermal expansion, adiabatic temperature gradient and potential temperature gradient of sea water, Deep-Sea Res. 20, 401-408

A. E. Gill, 1982 Atmosphere-Ocean Dynamics, Academic Press.

UNESCO 1981, Tenth report of the joint panel on oceanographic tables

and standards, Unesco technical papers in marine science, 36.

UNESCO 1983, N.P. Fofonoff and R.C. Millard Jr., Algorithms for computation of fundamental properties of seawater, Unesco technical papers in marine science, 44.

Author

Bjørn Ådlandsvik <bjorn@imr.no>
Institute of Marine Research
Version 1.1 November 2004
Version 1.2 January 2015