Select an equation of state

INTERFACE:

    REALTYPE function eqstate1(S,T,p,g,rho_0)

DESCRIPTION:

Calculates the in-situ buoyancy according to the selected method. S is salinity $S$ in psu, T is potential temperature $\theta$ in $^{\circ}$C (ITS-90), p is gauge pressure (absolute pressure - 10.1325 bar), g is the gravitational acceleration in ms$^{-2}$ and rho_0 the reference density in kgm$^{-3}$. eqstate1 is the in-situ-density in kgm$^{-3}$. For eq_state_method=1, the UNESCO equation of state is used, for eq_state_method=2, the Jackett et al. (2005) equation of state is used. Here, some care is needed, since the UNESCO equation used bar for pressure and the Jackett et al. (2005) uses dbar for pressure. For values of eq_state_method ranging from 1 to 4, one of the following methods will be used.

1. the full equation of state for sea water including pressure dependence.
2. the equation of state for sea water with the pressure evaluated at the sea surface as reference level. This is the choice for computations based on potential temperature and density.
3. a linearised equation of state. The parameters T0, S0 and p0 have to be specified in the namelist.
4. a linear equation of state with prescribed rho0, T0, S0, dtr0, dsr0 according to

   $$\rho = \rho_0 + (T - T_0) + (S - S_0) \quad .$$ (243)

   
   

USES:

    IMPLICIT NONE

INPUT PARAMETERS:

    REALTYPE,intent(in)                 :: S,T,p
    REALTYPE,optional,intent(in)        :: g,rho_0

REVISION HISTORY:

    Original author(s): Hans Burchard & Karsten Bolding