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

#include "tsmbkind.h"

USE yoesw    , ONLY : apad     ,bpad     ,d


IMPLICIT NONE


!     DUMMY INTEGER SCALARS
integer_m :: ka
integer_m :: kfdia
integer_m :: kidia
integer_m :: klon
integer_m :: knu



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

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

real_b :: pu(klon), ptr(klon)

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

!*       0.2   LOCAL ARRAYS
!              ------------

real_b :: zr1(klon), zr2(klon)

!     LOCAL INTEGER SCALARS
integer_m :: jl


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

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


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)) * (_one_ - d(knu,ka)) + d(knu,ka)
ENDDO

RETURN
END SUBROUTINE swtt