TwoStream

INTERFACE:

   subroutine TwoStream (lbc, ubc, lbp, ubp, filter_vegsol, num_vegsol, &
                         coszen, vai, rho, tau, ftdi, gdir)

DESCRIPTION:

   Two-stream fluxes for canopy radiative transfer
   Use two-stream approximation of Dickinson (1983) Adv Geophysics
   25:305-353 and Sellers (1985) Int J Remote Sensing 6:1335-1372
   to calculate fluxes absorbed by vegetation, reflected by vegetation,
   and transmitted through vegetation for unit incoming direct or diffuse
   flux given an underlying surface with known albedo.

USES:

     use shr_kind_mod, only: r8 => shr_kind_r8
     use clmtype
     use clm_varpar, only : numrad
     use clm_varcon, only : omegas, tfrz, betads, betais

ARGUMENTS:

     implicit none
     integer , intent(in)  :: lbc, ubc                 ! column bounds
     integer , intent(in)  :: lbp, ubp                 ! pft bounds
     integer , intent(in)  :: filter_vegsol(ubp-lbp+1) ! filter for vegetated 
     integer , intent(in)  :: num_vegsol               ! number of vegetated p
     real(r8), intent(in)  :: coszen(lbp:ubp)          ! cosine solar zenith a
     real(r8), intent(in)  :: vai(lbp:ubp)             ! elai+esai
     real(r8), intent(in)  :: rho(lbp:ubp,numrad)      ! leaf/stem refl weight
     real(r8), intent(in)  :: tau(lbp:ubp,numrad)      ! leaf/stem tran weight
     real(r8), intent(out) :: ftdi(lbp:ubp,numrad)     ! down direct flux belo
     real(r8), intent(out) :: gdir(lbp:ubp)            ! aver projected leaf/s

CALLED FROM:

   subroutine SurfaceAlbedo in this module

REVISION HISTORY:

   Author: Gordon Bonan
   Modified for speedup: Mariana Vertenstein, 8/26/02
   Vectorized routine: Mariana Vertenstein:  8/20/03

LOCAL VARIABLES:

   local pointers to implicit in scalars
     integer , pointer :: pcolumn(:)    ! column of corresponding pft
     real(r8), pointer :: albgrd(:,:)   ! ground albedo (direct) (column-level
     real(r8), pointer :: albgri(:,:)   ! ground albedo (diffuse)(column-level
     real(r8), pointer :: t_veg(:)      ! vegetation temperature (Kelvin)
     real(r8), pointer :: fwet(:)       ! fraction of canopy that is wet (0 to
     integer , pointer :: ivt(:)        ! pft vegetation type
     real(r8), pointer :: xl(:)         ! ecophys const - leaf/stem orientatio
   local pointers to implicit out scalars
     real(r8), pointer :: albd(:,:)     ! surface albedo (direct)
     real(r8), pointer :: albi(:,:)     ! surface albedo (diffuse)
     real(r8), pointer :: fabd(:,:)     ! flux absorbed by veg per unit direct
     real(r8), pointer :: fabi(:,:)     ! flux absorbed by veg per unit diffus
     real(r8), pointer :: ftdd(:,:)     ! down direct flux below veg per unit 
     real(r8), pointer :: ftid(:,:)     ! down diffuse flux below veg per unit
     real(r8), pointer :: ftii(:,:)     ! down diffuse flux below veg per unit