! File %M% from Library %Q%
! Version %I% from %G% extracted: %H%
!------------------------------------------------------------------------------

REAL (KIND = ireals) FUNCTION SfcFlx_wvpreswetbulb (T_dry, T_wetbulb, satwvpres_bulb, P)             

!------------------------------------------------------------------------------
!
! Description:
!
!  Computes water vapour pressure as function of air temperature, 
!  wet bulb temperature, satururation vapour pressure at wet-bulb temperature,
!  and air pressure.
!  
!
! Current Code Owner: DWD, Dmitrii Mironov
!  Phone:  +49-69-8062 2705
!  Fax:    +49-69-8062 3721
!  E-mail: dmitrii.mironov@dwd.de
!
! History:
! Version    Date       Name
! ---------- ---------- ----
! 1.00       2005/11/17 Dmitrii Mironov 
!  Initial release
! !VERSION!  !DATE!     <Your name>
!  <Modification comments>
!
! Code Description:
! Language: Fortran 90.
! Software Standards: "European Standards for Writing and
! Documenting Exchangeable Fortran 90 Code".
!==============================================================================
!
! Declarations:
!
! Modules used:

!_dm Parameters are USEd in module "SfcFlx".
!_nu USE data_parameters , ONLY : &
!_nu     ireals,                  & ! KIND-type parameter for real variables
!_nu     iintegers                  ! KIND-type parameter for "normal" integer variables

!==============================================================================

IMPLICIT NONE

!==============================================================================
!
! Declarations
 
!  Input (function argument) 
REAL (KIND = ireals), INTENT(IN) ::   &
  T_dry                             , & ! Dry air temperature [K]
  T_wetbulb                         , & ! Wet bulb temperature [K]
  satwvpres_bulb                    , & ! Satururation vapour pressure at wet-bulb temperature [N m^{-2}]
  P                                     ! Atmospheric pressure [N m^{-2}]

!==============================================================================
!  Start calculations
!------------------------------------------------------------------------------

! Water vapour pressure [N m^{-2} = kg m^{-1} s^{-2}]

SfcFlx_wvpreswetbulb = satwvpres_bulb & 
                     - tpsf_c_a_p*P/tpsf_L_evap/tpsf_Rd_o_Rv*(T_dry-T_wetbulb)


!------------------------------------------------------------------------------
!  End calculations
!==============================================================================

END FUNCTION SfcFlx_wvpreswetbulb