SUBROUTINE calc_liquid_water_content

!--------------------------------------------------------------------------------!
! This file is part of PALM.
!
! PALM is free software: you can redistribute it and/or modify it under the terms
! of the GNU General Public License as published by the Free Software Foundation,
! either version 3 of the License, or (at your option) any later version.
!
! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
! A PARTICULAR PURPOSE.  See the GNU General Public License for more details.
!
! You should have received a copy of the GNU General Public License along with
! PALM. If not, see <http://www.gnu.org/licenses/>.
!
! Copyright 1997-2012  Leibniz University Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
!
! Former revisions:
! -----------------
! $Id: calc_liquid_water_content.f90 1037 2012-10-22 14:10:22Z hoffmann $
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 667 2010-12-23 12:06:00Z suehring/gyschka
! nxl-1, nxr+1, nys-1, nyn+1 replaced by nxlg, nxrg, nysg, nyng
!
! 95 2007-06-02 16:48:38Z raasch
! hydro_press renamed hyp
!
! 19 2007-02-23 04:53:48Z raasch
! Old comment removed
!
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.5  2005/03/26 15:22:06  raasch
! Arguments for non-cyclic boundary conditions added to argument list of
! routine exchange_horiz,
! ql calculated for the ghost points, exchange of ghost points removed
!
! Revision 1.1  2000/04/13 14:50:45  schroeter
! Initial revision
!
!
!
! Description:
! ------------
! Calculation of the liquid water content (0%-or-100%-scheme)
!------------------------------------------------------------------------------!


    USE arrays_3d
    USE cloud_parameters
    USE constants
    USE grid_variables
    USE indices
    USE pegrid

    IMPLICIT NONE

    INTEGER :: i, j, k

    REAL :: alpha, e_s, q_s, t_l

    DO  i = nxlg, nxrg
       DO  j = nysg, nyng
          DO  k = nzb_2d(j,i)+1, nzt

!
!--          Compute the liquid water temperature
             t_l = t_d_pt(k) * pt(k,j,i)

!
!--          Compute saturation water vapor pressure at t_l
             e_s = 610.78 * EXP( 17.269 * ( t_l - 273.16 ) / &
                                          ( t_l - 35.86 ) )

!
!--          Compute approximation of saturation humidity
             q_s = 0.622 * e_s / ( hyp(k) - 0.378 * e_s )

!
!--          Correction factor
             alpha = 0.622 * l_d_r * l_d_cp / ( t_l * t_l )

!
!--          Correction of the approximated value
!--          (see: Cuijpers + Duynkerke, 1993, JAS, 23)
             q_s = q_s * ( 1.0 + alpha * q(k,j,i) ) / ( 1.0 + alpha * q_s )

!
!--          Compute the liquid water content
             IF ( ( q(k,j,i) - q_s ) > 0.0 ) THEN
                ql(k,j,i) = q(k,j,i) - q_s
             ELSE
                ql(k,j,i) = 0.0 
             ENDIF

          ENDDO
       ENDDO
    ENDDO
    
 END SUBROUTINE calc_liquid_water_content