PhaseChange

INTERFACE:

   subroutine PhaseChange (fact,   brr, hs, dhsdT, &   
                           tssbef, xmf, c)

DESCRIPTION:

   Calculation of the phase change within snow and soil layers:
   (1) Check the conditions for which the phase change may take place, 
       i.e., the layer temperature is great than the freezing point 
       and the ice mass is not equal to zero (i.e. melting), 
       or the layer temperature is less than the freezing point 
       and the liquid water mass is not equal to zero (i.e. freezing).
   (2) Assess the rate of phase change from the energy excess (or deficit) 
       after setting the layer temperature to freezing point.
   (3) Re-adjust the ice and liquid mass, and the layer temperature

USES:

     use shr_kind_mod, only: r8 => shr_kind_r8
     use clmtype
     use globals, only: dtime
     use clm_varcon, only : tfrz, hfus
     use clm_varpar, only : nlevsoi

ARGUMENTS:

     implicit none
     type (column_type),target,intent(inout):: c	      !column derived type
     real(r8), intent(in) :: tssbef(c%cps%snl+1:nlevsoi) !temperature at previous time step [K]
     real(r8), intent(in) :: brr   (c%cps%snl+1:nlevsoi) !
     real(r8), intent(in) :: fact  (c%cps%snl+1:nlevsoi) !temporary variables
     real(r8), intent(in) :: hs                          !net ground heat flux into the surface
     real(r8), intent(in) :: dhsdT                       !temperature derivative of "hs"
     real(r8), intent(out):: xmf                         !total latent heat of phase change

CALLED FROM:

   subroutine SoilTemperature in this module

REVISION HISTORY:

   15 September 1999: Yongjiu Dai; Initial code
   15 December 1999:  Paul Houser and Jon Radakovich; F90 Revision 
   2/14/02, Peter Thornton: Migrated to new data structures.

LOCAL VARIABLES:

   local pointers to original implicit in scalars
     integer , pointer :: snl          !number of snow layers
     real(r8), pointer :: h2osno       !snow water (mm H2O)
   local pointers to original implicit inout scalars
     real(r8), pointer :: snowdp       !snow height (m)
   local pointers tooriginal implicit out scalars
     real(r8), pointer :: qflx_snomelt !snow melt (mm H2O /s)
     real(r8), pointer :: eflx_snomelt !snow melt heat flux (W/m**2)
   local pointers to original implicit in arrays
     real(r8), dimension(:), pointer :: h2osoi_liq  !liquid water (kg/m2) (new)
     real(r8), dimension(:), pointer :: h2osoi_ice  !ice lens (kg/m2) (new)
   local pointers to original implicit inout arrays
     real(r8), dimension(:), pointer :: t_soisno !soil temperature (Kelvin)
   local pointers to original implicit out arrays
     integer, dimension(:), pointer ::  imelt !flag for melting (=1), freezing (=2), Not=0 (new)