*=*=*=*= LWTT.html =*=*=*=*
SUBROUTINE LWTT

SUBROUTINE LWTT


      SUBROUTINE LWTT (KDLON,PGA,PGB,PUU,PTT)
      IMPLICIT NONE
C
#include "dimensions.h"
#include "dimphys.h"
#include "dimradmars.h"
#include "yomlw.h"
C
C**** *LWTT* - LONGWAVE TRANSMISSION FUNCTIONS
C
C     PURPOSE.
C     --------
C           THIS ROUTINE COMPUTES THE TRANSMISSION FUNCTIONS FOR ALL THE
C     ABSORBERS (H2O, UNIFORMLY MIXED GASES, AND O3) IN ALL SIX SPECTRAL
C     INTERVALS.
C
C**   INTERFACE.
C     ----------
C          *LWTT* IS CALLED FROM *LWV*.
C
C     SUBROUTINE LWTT (KDLON,KND,KT,PUU,PTT)
C
C        EXPLICIT ARGUMENTS :
C        --------------------
C     ==== INPUTS ===
C KND    :                     ; WEIGHTING INDEX
C KT     :                     ; TEMPERATURE INDEX
C PUU    : (KDLON,NUA)         ; ABSORBER AMOUNTS
C     ==== OUTPUTS ===
C PTT    : (KDLON,NTRA)        ; TRANSMISSION FUNCTIONS
C
C        IMPLICIT ARGUMENTS :   NONE
C        --------------------
C
C     METHOD.
C     -------
C
C          1. TRANSMISSION FUNCTION BY H2O AND UNIFORMLY MIXED GASES ARE
C     COMPUTED USING PADE APPROXIMANTS AND HORNER'S ALGORITHM.
C          2. TRANSMISSION BY O3 IS EVALUATED WITH MALKMUS'S BAND MODEL.
C          3. TRANSMISSION BY H2O CONTINUUM AND AEROSOLS FOLLOW AN
C     A SIMPLE EXPONENTIAL DECREASE WITH ABSORBER AMOUNT.
C
C     EXTERNALS.
C     ----------
C
C          NONE
C
C     REFERENCE.
C     ----------
C
C        SEE RADIATION'S PART OF THE MODEL'S DOCUMENTATION AND
C        ECMWF RESEARCH DEPARTMENT DOCUMENTATION OF THE "IN CORE MODEL"
C
C     AUTHOR.
C     -------
C        JEAN-JACQUES MORCRETTE  *ECMWF*
C
C     MODIFICATIONS.
C     --------------
C        ORIGINAL : 88-12-15
C-----------------------------------------------------------------------
C
C
C-----------------------------------------------------------------------
C
C
C*        0.1   ARGUMENTS
C               ---------
C
      INTEGER kdlon
      REAL PUU(NDLO2,NUA), PTT(NDLO2,NTRA)
      REAL PGA(NDLO2,3,2),PGB(NDLO2,3,2)
C
C     ------------------------------------------------------------------
C
C*        0.2   LOCAL ARRAYS
C               ------------
C
      INTEGER JA,JL,jabs
      REAL ZXN(NDLON),ZXD(NDLON),zueq(ndlon)
C
c-----------------------------------------------------------------------
c   Transmission by the CO2 15 microns band:
c   ----------------------------------------

      DO  ja=1,2
       jabs=ja*2-1

c   equivalent absorber amount (Doppler effect):
c   --------------------------------------------

       DO jl=1,kdlon
          zueq(jl)=SQRT(puu(jl,jabs+1))
     s      +cst_voigt(1,ja)*puu(jl,jabs)**cst_voigt(2,ja)
       ENDDO

c   Horner's algorithm:
c   -------------------

         DO jl=1,kdlon
            zxn(jl) = pga(jl,1,ja) +
     1      zueq(jl)*(pga(jl,2,ja) + zueq(jl) * pga(jl,3,ja) )
            zxd(jl) = pgb(jl,1,ja) + zueq(jl)*(pgb(jl,2,ja) +
     1      zueq(jl) * ( pgb(jl,3,ja) + zueq(jl)  ))
            ptt(jl,ja) = zxn(jl) / zxd(jl)
       ENDDO
      ENDDO

      RETURN
      END