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ice_albedo.F90
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!***********************************************************************
!* GNU Lesser General Public License
!*
!* This file is part of the GFDL Flexible Modeling System (FMS).
!*
!* FMS is free software: you can redistribute it and/or modify it under
!* the terms of the GNU Lesser General Public License as published by
!* the Free Software Foundation, either version 3 of the License, or (at
!* your option) any later version.
!*
!* FMS is distributed in the hope that it will be useful, but WITHOUT
!* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
!* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
!* for more details.
!*
!* You should have received a copy of the GNU Lesser General Public
!* License along with FMS. If not, see <http://www.gnu.org/licenses/>.
!***********************************************************************
module ice_albedo_mod
!=======================================================================
!
! ICE SURFACE ALBEDO MODULE
!
! Routines for computing the surface albedo over ice
!
!=======================================================================
#ifdef INTERNAL_FILE_NML
use mpp_mod, only: input_nml_file
#else
use fms_mod, only: open_namelist_file
#endif
use fms_mod, only: error_mesg, file_exist, &
check_nml_error, &
FATAL, close_file, mpp_pe, mpp_root_pe, &
write_version_number, stdlog
implicit none
private
!======= public interface =============================================
public ice_albedo, ice_albedo_init
!--------------------- version number ----------------------------------
character(len=128) :: version = '$Id$'
character(len=128) :: tagname = '$Name$'
!=======================================================================
! DEFAULT VALUES OF NAMELIST PARAMETERS:
real :: crit_thickness = 1.00
real :: t_range = 10.0
real :: min_ice_alb = 0.50
real :: max_ice_alb = 0.80
real :: const_alb = 0.65
namelist /ice_albedo_nml/ crit_thickness , &
t_range , &
min_ice_alb , &
max_ice_alb , &
const_alb
!=======================================================================
! OTHER MODULE VARIABLES
real :: temp_ice_freeze
logical :: do_init = .true.
CONTAINS
!#######################################################################
subroutine ice_albedo_init ( t_freeze )
real, intent(in) :: t_freeze
integer unit, io, ierr
temp_ice_freeze = t_freeze
!------------------- read namelist input -------------------------------
#ifdef INTERNAL_FILE_NML
read (input_nml_file, nml=ice_albedo_nml, iostat=io)
ierr = check_nml_error(io, 'ice_albedo_nml')
#else
if (file_exist('input.nml')) then
unit = open_namelist_file ('input.nml')
ierr=1; do while (ierr /= 0)
read (unit, nml=ice_albedo_nml, iostat=io, end=10)
ierr = check_nml_error(io,'ice_albedo_nml')
enddo
10 call close_file (unit)
endif
#endif
!------- write version number and namelist ---------
if ( mpp_pe() == mpp_root_pe() ) then
call write_version_number(version, tagname)
unit = stdlog()
write (unit, nml=ice_albedo_nml)
endif
do_init = .false.
end subroutine ice_albedo_init
!#######################################################################
subroutine ice_albedo (ice, thickness, temp, albedo, i1, j1)
!-----------------------------------------------------------------------
!----------- CALCULATE SURFACE ALBEDO OVER ICE ------------------------
!-----------------------------------------------------------------------
!
! INPUT
! (i1,j1) = postition in global ice grid of first elements in
! the input
! thickness = thickness of ice (in meters)
! alb_ocean - albedo of open ocean (on ice grid)
! temp = surface temperature (in degrees kelvin)
!
! OUTPUT
! albedo = surface albedo
logical, intent(in), dimension(:,:,:) :: ice
real, intent(in), dimension(:,:,:) :: temp, thickness
real, intent(inout), dimension(:,:,:) :: albedo
integer, intent(in), optional :: i1, j1
!-----------------------------------------------------------------------
integer :: is, js, ie, je, n
real :: tcrit
real, dimension(size(temp,1),size(temp,2)) :: thick_ice_alb, alb_ocean
if (do_init) call error_mesg ('ice_albedo', &
'initialization not called', FATAL)
is = 1; if (present(i1)) is = i1
js = 1; if (present(j1)) js = j1
ie = is + size(temp,1) - 1
je = js + size(temp,2) - 1
tcrit = temp_ice_freeze - t_range
!--- first partition assumed to be open ocean ----
alb_ocean = albedo(:,:,1)
do n = 2, size(temp,3)
where(ice(:,:,n) .and. temp(:,:,n) <= tcrit) &
thick_ice_alb = max_ice_alb
where(ice(:,:,n) .and. temp(:,:,n) >= temp_ice_freeze) &
thick_ice_alb = min_ice_alb
where(ice(:,:,n) .and. temp(:,:,n) < temp_ice_freeze &
.and. temp(:,:,n) > tcrit) &
thick_ice_alb = max_ice_alb + &
(min_ice_alb - max_ice_alb)*(temp(:,:,n) - tcrit)/t_range
where (ice(:,:,n).and.thickness(:,:,n) >= crit_thickness) &
albedo(:,:,n) = thick_ice_alb
where (ice(:,:,n).and.thickness(:,:,n) < crit_thickness) &
albedo(:,:,n) = alb_ocean + &
(thick_ice_alb - alb_ocean) *sqrt(thickness(:,:,n)/crit_thickness)
end do
end subroutine ice_albedo
!######################################################################
end module ice_albedo_mod