SUBROUTINE init_cloud_physics

!--------------------------------------------------------------------------------!
! 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 1997-2014 Leibniz Universitaet Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
! 
! 
! Former revisions:
! ------------------
! $Id: init_cloud_physics.f90 1362 2014-04-16 15:19:12Z witha $
!
! 1361 2014-04-16 15:17:48Z hoffmann
! sed_qc_const is now calculated here (2-moment microphysics)
! 
! 1353 2014-04-08 15:21:23Z heinze
! REAL constants provided with KIND-attribute
! 
! 1334 2014-03-25 12:21:40Z heinze
! Bugfix: REAL constants provided with KIND-attribute
!
! 1322 2014-03-20 16:38:49Z raasch
! REAL constants defined as wp-kind
! 
! 1320 2014-03-20 08:40:49Z raasch
! ONLY-attribute added to USE-statements,
! kind-parameters added to all INTEGER and REAL declaration statements, 
! kinds are defined in new module mod_kinds, 
! revision history before 2012 removed,
! comment fields (!:) to be used for variable explanations added to
! all variable declaration statements 
!
! 1065 2012-11-22 17:42:36Z hoffmann
! The Courant number of sedimentation can be controlled with c_sedimentation. 
!
! 1053 2012-11-13 17:11:03Z hoffmann
! calculation of the maximum timestep according to the terminal velocity of rain 
! drops in the two moment cloud scheme
!
! calculation of frequently used constants (pirho_l, dpirho_l, schmidt_p_1d3, 
! hyrho) 
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 824 2012-02-17 09:09:57Z raasch
! calculation of b_cond replaced by calculation of bfactor
!
! Revision 1.1  2000/04/13 14:37:22  schroeter
! Initial revision
!
!
! Description:
! ------------
! Initialization of parameters for handling cloud-physics
!------------------------------------------------------------------------------!

    USE arrays_3d,                                                             &
        ONLY:  dzu, hyp, pt_init, zu
        
    USE cloud_parameters,                                                      &
        ONLY:  bfactor, cp, c_sedimentation, dpirho_l, dt_precipitation,       &
               hyrho, k_st, l_d_cp, l_d_r, l_d_rv, l_v, mass_of_solute,  &
               molecular_weight_of_solute, molecular_weight_of_water, pirho_l, &
               pt_d_t, rho_l, r_d, r_v, sed_qc_const, schmidt, schmidt_p_1d3,  &
               sigma_gc, t_d_pt, vanthoff, w_precipitation
        
    USE constants,                                                             &
        ONLY:  pi
        
    USE control_parameters,                                                    &
        ONLY:  g, icloud_scheme, message_string, precipitation, pt_surface,    &
               rho_surface, surface_pressure
    
    USE indices,                                                               &
        ONLY:  nzb, nzt
    
    USE kinds

    IMPLICIT NONE

    INTEGER(iwp) ::  k      !:
    
    REAL(wp) ::  t_surface  !:

    ALLOCATE( hyp(nzb:nzt+1), pt_d_t(nzb:nzt+1), t_d_pt(nzb:nzt+1),            &
              hyrho(nzb:nzt+1) )

!
!-- Calculate frequently used parameters
    l_d_cp = l_v / cp
    l_d_r  = l_v / r_d
    l_d_rv = l_v / r_v

    schmidt_p_1d3 = schmidt**( 1.0_wp / 3.0_wp )

    pirho_l  = pi * rho_l / 6.0_wp
    dpirho_l = 1.0_wp / pirho_l
!
!-- constant fot the sedimentation of cloud water (2-moment cloud physics)
    sed_qc_const = k_st * ( 3.0_wp / ( 4.0_wp * pi * rho_l )                   &
                          )**( 2.0_wp / 3.0_wp ) *                             &
                   EXP( 5.0_wp * LOG( sigma_gc )**2 )
!
!-- Calculate timestep according to precipitation
    IF ( icloud_scheme == 0  .AND.  precipitation )  THEN
       dt_precipitation = c_sedimentation * MINVAL( dzu(nzb+2:nzt) ) /         &
                          w_precipitation
    ENDIF
!
!-- Calculate factor used in equation for droplet growth by condensation
    bfactor = 3.0_wp * vanthoff * mass_of_solute * molecular_weight_of_water   &
              / ( 4.0_wp * pi * rho_l * molecular_weight_of_solute )
!
!-- Calculate:
!-- pt / t : ratio of potential and actual temperature (pt_d_t)
!-- t / pt : ratio of actual and potential temperature (t_d_pt)
!-- p_0(z) : vertical profile of the hydrostatic pressure (hyp)
    t_surface = pt_surface * ( surface_pressure / 1000.0_wp )**0.286_wp
    DO  k = nzb, nzt+1
!
!--    Check temperature in case of too large domain height
       IF ( ( t_surface - g/cp * zu(k) ) < 0.0_wp )  THEN
          WRITE( message_string, * )  'absolute temperature < 0.0 at zu(', k, &
                                      ') = ', zu(k)
          CALL message( 'init_cloud_physics', 'PA0142', 1, 2, 0, 6, 0 )
       ENDIF
       hyp(k)    = surface_pressure * 100.0_wp * &
                   ( (t_surface - g/cp * zu(k)) / t_surface )**(1.0_wp/0.286_wp)
       pt_d_t(k) = ( 100000.0_wp / hyp(k) )**0.286_wp
       t_d_pt(k) = 1.0_wp / pt_d_t(k)
       hyrho(k)  = hyp(k) / ( r_d * t_d_pt(k) * pt_init(k) )       
    ENDDO

!
!-- Compute reference density
    rho_surface = surface_pressure * 100.0_wp / ( r_d * t_surface )


 END SUBROUTINE init_cloud_physics