21 Surface Fractions

21.1 Module frac_mod - handles surface fractions. (Source File: frac_mod.F90)

Defines, declares, initializes, and updates surface fractions.

These fractions are used for merging fields onto various domains. This particular implementation of this module makes certain assumptions about which domains exist and the relationships between them. These assumptions are hard-coded into this software implementation.

ASSUMPTIONS:

• atm and lnd grid cells and domain decompostion are identical
• ice and ocn domains are identical (includes decomposition)
• all atm cells are fully active
• all ocn cells are either fully active or fully inactive
• lnd cells can be partially active - the fraction of a lnd cell that is active is the fraction that is not occupied by ocn
• ice cells can be partially active - the fraction that is active is determined by the ice component itself

For each domain (atm,lnd,ice,ocn) there are four fractions: $f_a,f_i,f_l,f_o,$ three that could be used for merging, and one which indicatates the fraction of the cell which is active.

• merging on atm domain: $F_a = f_i F_i + f_l F_l + f_o F_o \hfil (f_i + f_l + f_o = 1)$
• merging on ice domain: $F_i = f_a F_a + f_o F_o = F_a + F_o \hfil (f_a = f_o = 1, f_l=0)$
• merging on lnd domain: $F_l = f_a F_a = F_a \hfil (f_a = 1, f_o = f_i = 0)$
• merging on ocn domain: $F_o = f_a F_a + f_o F_o \hfil (f_a + f_i = 1, f_l = 0)$
• on the atm domain: $f_a = 1$ (atm cells are fully active)
• on the ice domain: $f_i$ is time-variant and determined by the ice model
• on the lnd domain: $f_l = 1 - f_o$ and is time-invariant
• on the ocn domain: $f_o = 1$ (ocn cells are fully active)

REVISION HISTORY:

       2002-Aug-21 - B. Kauffman, 1st version.

INTERFACE:

 
 module frac_mod

USES:

 
    use shr_sys_mod         ! shared system routines
    use shr_timer_mod       ! shared timer routines
    use shr_mpi_mod         ! shared mpi layer
    use cpl_kind_mod        ! kinds
    use cpl_comm_mod        ! mpi/mph communicator info
    use cpl_mct_mod         ! mct interface
    use cpl_const_mod       ! constants
    use cpl_domain_mod      ! defines domain
    use cpl_bundle_mod      ! defines bundle
    use cpl_map_mod         ! access to map data types and methods
    use cpl_control_mod, only: dbug=>cpl_control_infoDBug
 
    implicit none
 
    private ! except

PUBLIC TYPES:

 
   ! no public types

PUBLIC MEMBER FUNCTIONS:

 
    public :: frac_init  ! one-time initialization of fraction values
    public :: frac_set   ! time-variant update of fraction values

PUBLIC DATA MEMBERS:

 
    !--- note: these could be declared in data_mod.F90            ---
    !--- or in a cpl/frac_mod.F90 & passed down from main program ---
 
    type(cpl_bundle),public :: bun_frac_a   ! surface fractions on atm domain
    type(cpl_bundle),public :: bun_frac_i   ! surface fractions on ice domain
    type(cpl_bundle),public :: bun_frac_l   ! surface fractions on lnd domain
    type(cpl_bundle),public :: bun_frac_o   ! surface fractions on ocn domain
 
    character(*),parameter :: frac_fields = 'afrac:ifrac:lfrac:ofrac'

21.1.1 frac_init - Initialize all the surface fraction bundles

Initialize all the fraction bundles bun_frac_* using the input domains domain_. All fractions are derived from the (time-invariant) ice/ocn domain masks plus the (time-variant) ice fraction.

This initialization routine sets the time-invariant values.

REVISION HISTORY:

       2002-aug-21 - B. Kauffman, 1st version.

INTERFACE:

 
 subroutine frac_init(map_o2a,domain_a,domain_i,domain_l,domain_o)

USES:

INPUT/OUTPUT PARAMETERS:

 
    type(cpl_map   ),intent(inout) :: map_o2a  ! use to map ice-frac from ocn -> atm
    type(cpl_domain),intent(in   ) :: domain_a ! domain of atm fraction bundle
    type(cpl_domain),intent(in   ) :: domain_i ! domain of ice fraction bundle
    type(cpl_domain),intent(in   ) :: domain_l ! domain of lnd fraction bundle
    type(cpl_domain),intent(in   ) :: domain_o ! domain of ocn fraction bundle

21.1.2 frac_set - set/update the surface fraction bundles

Set/update the fraction bundles to account for time varying sea-ice distribution using the ice fraction information in the input real array ifrac_i.

Update bun_frac_i, then bun_frac_o, then use map_o2a to update bun_frac_a. Make use of bun_frac_l.

The companion initialization routine frac_init must be called first to set the time-invariant values.

REMARKS:

       The domain_* arguments should be removed because they aren't used.

REVISION HISTORY:

       2002-aug-21 - B. Kauffman, 1st version.

INTERFACE:

 
 subroutine frac_set(ifrac_i,map_o2a,domain_a,domain_i,domain_l,domain_o)

USES:

INPUT/OUTPUT PARAMETERS:

 
    real(R8)        ,intent(in   ) :: ifrac_i(:) ! temporary data array on atm domain
    type(cpl_map   ),intent(inout) :: map_o2a    ! use to map ifrac from ocn -> atm
    type(cpl_domain),intent(in   ) :: domain_a   ! domain of atm fraction bundle
    type(cpl_domain),intent(in   ) :: domain_i   ! domain of ice fraction bundle
    type(cpl_domain),intent(in   ) :: domain_l   ! domain of lnd fraction bundle
    type(cpl_domain),intent(in   ) :: domain_o   ! domain of ocn fraction bundle