swtt.F90

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SUBROUTINE swtt ( KIDIA, KFDIA, KLON, KNU, KA , PU, PTR)

!**** *SWTT* - COMPUTES THE SHORTWAVE TRANSMISSION FUNCTIONS

!     PURPOSE.
!     --------
!           THIS ROUTINE COMPUTES THE TRANSMISSION FUNCTIONS FOR ALL THE
!     ABSORBERS (H2O, UNIFORMLY MIXED GASES, AND O3) IN THE TWO SPECTRAL
!     INTERVALS.

!**   INTERFACE.
!     ----------
!          *SWTT* IS CALLED FROM *SW1S*, *SWNI*.

!        EXPLICIT ARGUMENTS :
!        --------------------
! KNU    :                     ; INDEX OF THE SPECTRAL INTERVAL
! KA     :                     ; INDEX OF THE ABSORBER
! PU     : (KLON)             ; ABSORBER AMOUNT
!     ==== OUTPUTS ===
! PTR    : (KLON)             ; TRANSMISSION FUNCTION

!        IMPLICIT ARGUMENTS :   NONE
!        --------------------

!     METHOD.
!     -------

!          TRANSMISSION FUNCTION ARE COMPUTED USING PADE APPROXIMANTS
!     AND HORNER'S ALGORITHM.

!     EXTERNALS.
!     ----------

!          NONE

!     REFERENCE.
!     ----------

!        SEE RADIATION'S PART OF THE MODEL'S DOCUMENTATION AND
!        ECMWF RESEARCH DEPARTMENT DOCUMENTATION OF THE IFS

!     AUTHOR.
!     -------
!        JEAN-JACQUES MORCRETTE  *ECMWF*

!     MODIFICATIONS.
!     --------------
!        ORIGINAL : 88-12-15
!        M.Hamrud      01-Oct-2003 CY28 Cleaning
   
!-----------------------------------------------------------------------

USE parkind1  ,ONLY : jpim     ,jprb
USE yomhook   ,ONLY : lhook,   dr_hook

USE yoesw    , ONLY : apad     ,bpad     ,d

IMPLICIT NONE

INTEGER(KIND=JPIM),INTENT(IN)    :: KLON 
INTEGER(KIND=JPIM),INTENT(IN)    :: KIDIA 
INTEGER(KIND=JPIM),INTENT(IN)    :: KFDIA 
INTEGER(KIND=JPIM),INTENT(IN)    :: KNU 
INTEGER(KIND=JPIM),INTENT(IN)    :: KA 
REAL(KIND=JPRB)   ,INTENT(IN)    :: PU(klon) 
REAL(KIND=JPRB)   ,INTENT(OUT)   :: PTR(klon) 
!-----------------------------------------------------------------------

!*       0.1   ARGUMENTS
!              ---------

!-----------------------------------------------------------------------

!              ------------

REAL(KIND=JPRB) :: ZR1(klon), ZR2(klon)

INTEGER(KIND=JPIM) :: JL
REAL(KIND=JPRB) :: ZHOOK_HANDLE

!-----------------------------------------------------------------------

!*         1.      HORNER'S ALGORITHM TO COMPUTE TRANSMISSION FUNCTION

IF (lhook) CALL dr_hook('SWTT',0,zhook_handle)
DO jl = kidia,kfdia
  zr1(jl) = apad(knu,ka,1) + pu(jl) * (apad(knu,ka,2) + pu(jl)&
   & * ( apad(knu,ka,3) + pu(jl) * (apad(knu,ka,4) + pu(jl)&
   & * ( apad(knu,ka,5) + pu(jl) * (apad(knu,ka,6) + pu(jl)&
   & * ( apad(knu,ka,7) ))))))  

  zr2(jl) = bpad(knu,ka,1) + pu(jl) * (bpad(knu,ka,2) + pu(jl)&
   & * ( bpad(knu,ka,3) + pu(jl) * (bpad(knu,ka,4) + pu(jl)&
   & * ( bpad(knu,ka,5) + pu(jl) * (bpad(knu,ka,6) + pu(jl)&
   & * ( bpad(knu,ka,7) ))))))  

!*         2.      ADD THE BACKGROUND TRANSMISSION

  ptr(jl) = (zr1(jl) / zr2(jl)) * (1.0_jprb - d(knu,ka)) + d(knu,ka)
ENDDO

IF (lhook) CALL dr_hook('SWTT',1,zhook_handle)
END SUBROUTINE swtt