cycalc.F90

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!
!=====================SUBROUTINE CYCALC=================================
subroutine cycalc( aparkk, vm, atheta, btheta, par, &
        gammas, resp_can, rrkk, omss, c3, c4, &
        pco2i, assimn, assim)
!=======================================================================
! calculates smoothed minimum photosynthetic rate equivelent to steps
! in figure 4 of SE-92A.  C4 calculation based on CO-92
!
! modifications:
!  Kevin Schaefer multiply assim and resp_can by aparkk separately (5/31/05)
!
! OUTPUT:   
!       ASSIM         
!       ASSIMN
!
! DIAGNOSTICS:
!       OMC            RUBISCO LIMITED ASSIMILATION (MOL M-2 S-1)
!       OME            LIGHT LIMITED ASSIMILATION (MOL M-2 S-1)
!       OMS            SINK LIMITED ASSIMILATION (MOL M-2 S-1)
!       CO2S           CANOPY SURFACE CO2 CONCENTRATION (MOL MOL-1)
!+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

    use kinds

    implicit none

    !Bio...INPUT VARIABLES
    real(kind=dbl_kind),intent(in) :: 
        aparkk,  ! (-) PAR use Parameter
        vm,      !
        atheta,  !
        btheta,  !
        gammas,  !
        par,     !
        resp_can,   ! (mole/m2/s) canopy autotrophic respiration
        rrkk,    !
        omss,    !
        c3,      !
        c4,      !
        pco2i     !

    !Bio...OUTPUT VARIABLES
    real(kind=dbl_kind),intent(out) :: 
        assimn,  !
        assim     !

    !Bio...LOCAL VARIABLES
    real(kind=dbl_kind) :: 
        ome,    !
        omc,    !
        omp,    !
        oms,    !
        sqrtin   !

    !-----------------------------------------------------------------------
    !     CALCULATE ASSIMILATION RATE
    !
    !      OMC         (OMEGA-C): EQUATION (11) , SE-92A
    !      OME         (OMEGA-E): EQUATION (12) , SE-92A
    !      OMS         (OMEGA-S): EQUATION (13) , SE-92A
    !      ASSIMN      (A-N)    : EQUATION (14,15), SE-92A
    !-----------------------------------------------------------------------

    omc = vm *(pco2i-gammas)/(pco2i + rrkk)*c3    &
        + vm * c4
    ome = par*(pco2i-gammas)/(pco2i+2.*gammas)*c3 &
        + par * c4
    sqrtin= MAX( 0.0_dbl_kind, ( (ome+omc)**2 - 4.*atheta*ome*omc ) )
    omp  = ( ( ome+omc ) - SQRT( sqrtin ) ) / ( 2.*atheta )
    oms  = omss * c3 + omss*pco2i * c4
    sqrtin= MAX( 0.0_dbl_kind, ( (omp+oms)**2 - 4.*btheta*omp*oms ) ) 
    assim = (( ( oms+omp ) - SQRT( sqrtin ) ) / ( 2.*btheta ))*aparkk
    assimn = assim - resp_can 

    return
end subroutine cycalc