saturation.F90

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module saturation_mod
  use datadefn_mod, only : default_precision
  implicit none

   real(kind=DEFAULT_PRECISION), parameter :: &
        tk0c = 273.15_default_precision,      &! Temperature of freezing in Kelvin
        qsa1 = 3.8_default_precision,         &! Top in equation to calculate qsat
        qsa2 = -17.2693882_default_precision, &! Constant in qsat equation
        qsa3 = 35.86_default_precision,       &! Constant in qsat equation
        qsa4 = 6.109_default_precision       ! Constant in qsat equation

   public qsaturation, dqwsatdt
contains

  real(kind=DEFAULT_PRECISION) function qsaturation(temperature, pressure)
    real(kind=DEFAULT_PRECISION), intent(in) :: temperature, pressure

    qsaturation = qsa1/(pressure*exp(qsa2*(temperature - tk0c)/(temperature - qsa3)) - qsa4)
  end function qsaturation  

  real(kind=DEFAULT_PRECISION) function dqwsatdt(saturation_mixing_ratio, temperature)
    real(kind=DEFAULT_PRECISION), intent(in) :: saturation_mixing_ratio, temperature
    
    dqwsatdt = -qsa2*(tk0c-qsa3)*(1.0_default_precision+qsa4*saturation_mixing_ratio/qsa1)*&
         saturation_mixing_ratio*(temperature-qsa3)**(-2.0_default_precision)
  end function dqwsatdt  
end module saturation_mod