USTAR_1D Function

FUNCTION USTAR_1D(PWIND,PZ,PZ0,PLMO)
  USE MODD_CSTS
  USE MODD_SURF_PAR,  ONLY : XUNDEF
  IMPLICIT NONE  
  REAL, DIMENSION(:), INTENT(IN)               :: PWIND
  REAL, DIMENSION(:), INTENT(IN)               :: PZ
  REAL, DIMENSION(:), INTENT(IN)               :: PZ0
  REAL, DIMENSION(:), INTENT(IN)               :: PLMO
  REAL, DIMENSION(SIZE(PZ))                    :: USTAR_1D

  REAL, DIMENSION(SIZE(PZ))                    :: ZZ_O_LMO
  REAL, DIMENSION(SIZE(PZ))                    :: ZZ0_O_LMO
  REAL(KIND=JPRB) :: ZHOOK_HANDLE
!
!* purely unstable case
  IF (LHOOK) CALL DR_HOOK('MODE_SBLS:USTAR_1D',0,ZHOOK_HANDLE)
  USTAR_1D (:) = 0.
  ZZ_O_LMO (:) = XUNDEF
  ZZ0_O_LMO(:) = XUNDEF
!
!* general case
  WHERE(ABS(PLMO) > 1.E-20 .AND. PLMO/=XUNDEF)
    ZZ_O_LMO  = PZ(:)  / PLMO(:)
    ZZ0_O_LMO = PZ0(:) / PLMO(:)
    USTAR_1D(:) = PWIND                                   &
                  * XKARMAN / ( LOG(PZ(:)/PZ0(:))           &
                               - PAULSON_PSIM(ZZ_O_LMO(:))  &
                               + PAULSON_PSIM(ZZ0_O_LMO(:)) )  
  END WHERE
!
!* purely neutral case
  WHERE(PLMO==XUNDEF)
    ZZ_O_LMO = 0.
    USTAR_1D(:) = PWIND     &
                    * XKARMAN / LOG(PZ(:)/PZ0(:))  
  END WHERE
IF (LHOOK) CALL DR_HOOK('MODE_SBLS:USTAR_1D',1,ZHOOK_HANDLE)
!
END FUNCTION USTAR_1D