USTAR_0D Function

FUNCTION USTAR_0D(PWIND,PZ,PZ0,PLMO)
  USE MODD_CSTS
  USE MODD_SURF_PAR,  ONLY : XUNDEF
  IMPLICIT NONE  
  REAL, INTENT(IN)               :: PWIND
  REAL, INTENT(IN)               :: PZ
  REAL, INTENT(IN)               :: PZ0
  REAL, INTENT(IN)               :: PLMO
  REAL                           :: USTAR_0D
  REAL(KIND=JPRB) :: ZHOOK_HANDLE
!
!* purely unstable case
  IF (LHOOK) CALL DR_HOOK('MODE_SBLS:USTAR_0D',0,ZHOOK_HANDLE)
  USTAR_0D = 0.
!
!* general case
  IF ( ABS(PLMO) >= 1.E-20 .AND. PLMO/=XUNDEF)    &
    USTAR_0D = PWIND * XKARMAN / ( LOG(PZ/PZ0) - PAULSON_PSIM(PZ/PLMO) + PAULSON_PSIM(PZ0/PLMO) )  
!
!* purely neutral case
  IF (PLMO==XUNDEF)                  &
    USTAR_0D = PWIND * XKARMAN / LOG(PZ/PZ0)  
IF (LHOOK) CALL DR_HOOK('MODE_SBLS:USTAR_0D',1,ZHOOK_HANDLE)

END FUNCTION USTAR_0D