gsw_ct_freezing_exact.f90

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!==========================================================================
elemental function gsw_ct_freezing_exact (sa, p, saturation_fraction)
!==========================================================================
!
!  Calculates the Conservative Temperature at which seawater freezes.  The 
!  Conservative Temperature freezing point is calculated from the exact 
!  in-situ freezing temperature which is found by a modified Newton-Raphson
!  iteration (McDougall and Wotherspoon, 2013) of the equality of the 
!  chemical potentials of water in seawater and in ice.
!
!  An alternative GSW function, gsw_CT_freezing_poly, it is based on a 
!  computationally-efficient polynomial, and is accurate to within -5e-4 K 
!  and 6e-4 K, when compared with this function.
!
!  SA  =  Absolute Salinity                                        [ g/kg ]
!  p   =  sea pressure                                             [ dbar ]
!         ( i.e. absolute pressure - 10.1325 dbar ) 
!  saturation_fraction = the saturation fraction of dissolved air in 
!                        seawater
!
!  CT_freezing = Conservative Temperature at freezing of seawater [ deg C ]
!--------------------------------------------------------------------------

use gsw_mod_toolbox, only : gsw_t_freezing_exact
use gsw_mod_toolbox, only : gsw_ct_from_t

use gsw_mod_kinds

implicit none

real (r8), intent(in) :: sa, p, saturation_fraction

real (r8) :: gsw_ct_freezing_exact

real (r8) :: t_freezing

t_freezing = gsw_t_freezing_exact(sa,p,saturation_fraction)
gsw_ct_freezing_exact = gsw_ct_from_t(sa,t_freezing,p)

return
end function

!--------------------------------------------------------------------------