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 1997-2012  Leibniz University Hannover
!--------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
!
! Former revisions:
! ------------------
! $Id: init_cloud_physics.f90 1054 2012-11-13 17:30:09Z raasch $
!
! 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
!
! 221 2009-01-12 15:32:23Z raasch
! Bugfix: abort in case that absolute temperature is below zero
!
! 95 2007-06-02 16:48:38Z raasch
! hydro_press renamed hyp
!
! February 2007
! RCS Log replace by Id keyword, revision history cleaned up
!
! Revision 1.5  2005/06/26 19:55:58  raasch
! Initialization of cloud droplet constants, gas_constant renamed r_d,
! latent_heat renamed l_v
!
! Revision 1.1  2000/04/13 14:37:22  schroeter
! Initial revision
!
!
! Description:
! ------------
! Initialization of parameters for handling cloud-physics
!------------------------------------------------------------------------------!

    USE arrays_3d
    USE cloud_parameters
    USE constants
    USE control_parameters
    USE grid_variables
    USE indices

    IMPLICIT NONE

    INTEGER ::  k
    REAL    ::  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 / 3.0 )

    pirho_l  = pi * rho_l / 6.0
    dpirho_l = 1.0 / pirho_l 
!
!-- Calculate timestep according to precipitation
    IF ( icloud_scheme == 0  .AND.  precipitation )  THEN
       dt_precipitation = MINVAL( dzu(nzb+2:nzt) ) / w_precipitation
    ENDIF
!
!-- Calculate factor used in equation for droplet growth by condensation
    bfactor = 3.0 * vanthoff * mass_of_solute * molecular_weight_of_water &
              / ( 4.0 * 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 )**0.286
    DO  k = nzb, nzt+1
!
!--    Check temperature in case of too large domain height
       IF ( ( t_surface - g/cp * zu(k) ) < 0.0 )  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 * &
                   ( (t_surface - g/cp * zu(k)) / t_surface )**(1.0/0.286)
       pt_d_t(k) = ( 100000.0 / hyp(k) )**0.286
       t_d_pt(k) = 1.0 / 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 / ( r_d * t_surface )


 END SUBROUTINE init_cloud_physics