surface_cd.F90

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!SFX_LIC Copyright 1994-2014 CNRS, Meteo-France and Universite Paul Sabatier
!SFX_LIC This is part of the SURFEX software governed by the CeCILL-C licence
!SFX_LIC version 1. See LICENSE, CeCILL-C_V1-en.txt and CeCILL-C_V1-fr.txt  
!SFX_LIC for details. version 1.
!   #################################################################
    SUBROUTINE surface_cd(PRI, PZREF, PUREF, PZ0EFF, PZ0H,   &
                              pcd, pcdn) 
!   #################################################################
!
!!****  *SURFACE_CD*  
!!
!!    PURPOSE
!!    -------
!
!     Computes the drag coefficients for momentum near the ground
!         
!     
!!**  METHOD
!!    ------
!
!
!
!    1 and 2 : computation of relative humidity near the ground
!
!    3 : richardson number
!
!    4 : the aerodynamical resistance for heat transfers is deduced
!
!    5 : the drag coefficient for momentum ZCD is computed
!
!
!!    EXTERNAL
!!    --------
!!
!!
!!    IMPLICIT ARGUMENTS
!!    ------------------
!!
!!    MODD_CST
!!    MODD_GROUND_PAR
!!
!!      
!!    REFERENCE
!!    ---------
!!
!!      
!!    AUTHOR
!!    ------
!!
!!      V. Masson           * Meteo-France *
!!
!!    MODIFICATIONS
!!    -------------
!!      Original    20/01/98 
!!                  02/04/01 (P Jabouille) limitation of Z0 with 0.5 PUREF
!-------------------------------------------------------------------------------
!
!*       0.     DECLARATIONS
!               ------------
!
USE modd_csts,ONLY : xkarman
!
USE mode_thermos
!
USE yomhook   ,ONLY : lhook,   dr_hook
USE parkind1  ,ONLY : jprb
!
IMPLICIT NONE
!
!*      0.1    declarations of arguments
!
!
REAL, DIMENSION(:), INTENT(IN)    :: pri      ! Richardson number
REAL, DIMENSION(:), INTENT(IN)    :: pzref    ! reference height of the first
                                              ! atmospheric level
REAL, DIMENSION(:), INTENT(IN)    :: puref    ! reference height of the wind
!                                             ! NOTE this is different from ZZREF
!                                             ! ONLY in stand-alone/forced mode,
!                                             ! NOT when coupled to a model (MesoNH)
REAL, DIMENSION(:), INTENT(IN)    :: pz0eff   ! roughness length for momentum
                                              ! with subgrid-scale orography
REAL, DIMENSION(:), INTENT(IN)    :: pz0h     ! roughness length for heat
!
REAL, DIMENSION(:), INTENT(OUT)   :: pcd      ! drag coefficient for momentum
REAL, DIMENSION(:), INTENT(OUT)   :: pcdn     ! neutral drag coefficient for momentum
!
!*      0.2    declarations of local variables
!
!
REAL                       :: zz0eff, zz0h, zmu,     &
                               zcmstar, zpm, zcm, zfm 
INTEGER                    :: jj
REAL(KIND=JPRB) :: zhook_handle

! Functions :
REAL :: x, cmstar, pm
 cmstar(x) = 6.8741 + 2.6933*x - 0.3601*x*x + 0.0154*x*x*x
pm(x) = 0.5233 - 0.0815*x + 0.0135*x*x - 0.0010*x*x*x

!-------------------------------------------------------------------------------
!
!*       1.     Drag coefficient for momentum transfers
!               ---------------------------------------
!

!
IF (lhook) CALL dr_hook('SURFACE_CD',0,zhook_handle)
DO jj=1,SIZE(pri)
  zz0eff = min(pz0eff(jj),puref(jj)*0.5)
  zz0h   = min(zz0eff,pz0h(jj))
!
  zmu = log( min(zz0eff/zz0h,200.) )
!
  pcdn(jj) = (xkarman/log(puref(jj)/zz0eff))**2

  zcmstar = cmstar(zmu)
  zpm     = pm(zmu)
!
  zcm = 10.*zcmstar*pcdn(jj)*( puref(jj)/zz0eff )**zpm
!
  IF ( pri(jj) > 0.0 ) THEN
    zfm = 1. + 10.*pri(jj) / sqrt( 1.+5.*pri(jj) )
    zfm = 1. / zfm
  ELSE
    zfm = 1. - 10.*pri(jj) / ( 1.+zcm*sqrt(-pri(jj)) )
  ENDIF
!
  pcd(jj) = pcdn(jj)*zfm
!
ENDDO
IF (lhook) CALL dr_hook('SURFACE_CD',1,zhook_handle)
!
!-------------------------------------------------------------------------------
!
END SUBROUTINE surface_cd