source: palm/trunk/SOURCE/diffusivities.f90 @ 2601

!> @file diffusivities.f90
!------------------------------------------------------------------------------!
! 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 1997-2017 Leibniz Universitaet Hannover
!------------------------------------------------------------------------------!
!
! Current revisions:
! -----------------
! 
! 
! Former revisions:
! -----------------
! $Id: diffusivities.f90 2365 2017-08-21 14:59:59Z scharf $
! Vertical grid nesting implemented (SadiqHuq)
! 
! 2233 2017-05-30 18:08:54Z suehring
!
! 2232 2017-05-30 17:47:52Z suehring
! Adjustments to new topography and surface concept
! 
! 2118 2017-01-17 16:38:49Z raasch
! OpenACC directives removed
! 
! 2031 2016-10-21 15:11:58Z knoop
! renamed variable rho to rho_ocean
! 
! 2000 2016-08-20 18:09:15Z knoop
! Forced header and separation lines into 80 columns
!
! 1711 2015-11-05 07:38:04Z raasch
! bugfix: loop moved into IF block to avoid usage of l without being defined
!
! 1682 2015-10-07 23:56:08Z knoop
! Code annotations made doxygen readable 
! 
! 1374 2014-04-25 12:55:07Z raasch
! rif removed from acc-present-list
! 
! 1353 2014-04-08 15:21:23Z heinze
! REAL constants provided with KIND-attribute 
! 
! 1340 2014-03-25 19:45:13Z kanani
! REAL constants defined as wp-kind
!
! 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 kinds, 
! revision history before 2012 removed,
! comment fields (!:) to be used for variable explanations added to
! all variable declaration statements 
!
! 1179 2013-06-14 05:57:58Z raasch
! use_reference renamed use_single_reference_value
!
! 1036 2012-10-22 13:43:42Z raasch
! code put under GPL (PALM 3.9)
!
! 1015 2012-09-27 09:23:24Z raasch
! OpenACC statements added + code changes required for GPU optimization,
! adjustment of mixing length to the Prandtl mixing length at first grid point
! above ground removed
!
! Revision 1.1  1997/09/19 07:41:10  raasch
! Initial revision
!
!
! Description:
! ------------
!> Computation of the turbulent diffusion coefficients for momentum and heat 
!> according to Prandtl-Kolmogorov
!------------------------------------------------------------------------------!
 SUBROUTINE diffusivities( var, var_reference )
 

    USE arrays_3d,                                                             &
        ONLY:  dd2zu, e, kh, km, l_grid, l_wall
        
    USE control_parameters,                                                    &
        ONLY:  atmos_ocean_sign, e_min, g, outflow_l, outflow_n, outflow_r,    &
               outflow_s, use_single_reference_value, wall_adjustment,         &
               wall_adjustment_factor
                
    USE indices,                                                               &
        ONLY:  nxl, nxlg, nxr, nxrg, nyn, nyng, nys, nysg, nzb, nzt,           &
               wall_flags_0
    USE kinds
    
    USE pegrid
    
    USE statistics,                                                            &
        ONLY :  rmask, statistic_regions, sums_l_l

    USE surface_mod,                                                           &
        ONLY :  bc_h

    USE vertical_nesting_mod,                                                  &
        ONLY:  vnest_boundary_conds_khkm, vnest_init

    IMPLICIT NONE

    INTEGER(iwp) ::  i                   !<
    INTEGER(iwp) ::  j                   !<
    INTEGER(iwp) ::  k                   !<
    INTEGER(iwp) ::  m                   !<
    INTEGER(iwp) ::  omp_get_thread_num  !<
    INTEGER(iwp) ::  sr                  !<
    INTEGER(iwp) ::  tn                  !<

    REAL(wp)     ::  dvar_dz             !<
    REAL(wp)     ::  flag                !<
    REAL(wp)     ::  l                   !<
    REAL(wp)     ::  ll                  !<
    REAL(wp)     ::  l_stable            !<
    REAL(wp)     ::  sqrt_e              !<
    REAL(wp)     ::  var_reference       !<

    REAL(wp)     ::  var(nzb:nzt+1,nysg:nyng,nxlg:nxrg)  !<


!
!-- Default thread number in case of one thread
    tn = 0

!
!-- Initialization for calculation of the mixing length profile
    sums_l_l = 0.0_wp

!
!-- Compute the turbulent diffusion coefficient for momentum
    !$OMP PARALLEL PRIVATE (dvar_dz,i,j,k,l,ll,l_stable,sqrt_e,sr,tn,flag)
!$  tn = omp_get_thread_num()

!
!-- Introduce an optional minimum tke
    IF ( e_min > 0.0_wp )  THEN
       !$OMP DO
       DO  i = nxlg, nxrg
          DO  j = nysg, nyng
             DO  k = nzb+1, nzt
                e(k,j,i) = MAX( e(k,j,i), e_min ) *                            &
                        MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j,i), 0 ) )
             ENDDO
          ENDDO
       ENDDO
    ENDIF

    !$OMP DO
    DO  i = nxlg, nxrg
       DO  j = nysg, nyng
          DO  k = nzb+1, nzt

             flag = MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j,i), 0 ) )

             sqrt_e = SQRT( e(k,j,i) )
!
!--          Determine the mixing length
             dvar_dz = atmos_ocean_sign * &  ! inverse effect of pt/rho_ocean gradient
                       ( var(k+1,j,i) - var(k-1,j,i) ) * dd2zu(k)
             IF ( dvar_dz > 0.0_wp ) THEN
                IF ( use_single_reference_value )  THEN
                   l_stable = 0.76_wp * sqrt_e /                               &
                                 SQRT( g / var_reference * dvar_dz ) + 1E-5_wp
                ELSE
                   l_stable = 0.76_wp * sqrt_e /                               &
                                 SQRT( g / var(k,j,i) * dvar_dz ) + 1E-5_wp
                ENDIF
             ELSE
                l_stable = l_grid(k)
             ENDIF
!
!--          Adjustment of the mixing length
             IF ( wall_adjustment )  THEN
                l  = MIN( wall_adjustment_factor * l_wall(k,j,i), l_grid(k),   &
                          l_stable )
                ll = MIN( wall_adjustment_factor * l_wall(k,j,i), l_grid(k) )
             ELSE
                l  = MIN( l_grid(k), l_stable )
                ll = l_grid(k)
             ENDIF
!
!--          Compute diffusion coefficients for momentum and heat
             km(k,j,i) = 0.1_wp * l * sqrt_e                      * flag
             kh(k,j,i) = ( 1.0_wp + 2.0_wp * l / ll ) * km(k,j,i) * flag
     

!
!--          Summation for averaged profile (cf. flow_statistics)
             DO  sr = 0, statistic_regions
                sums_l_l(k,sr,tn) = sums_l_l(k,sr,tn) + l * rmask(j,i,sr)      &
                                                          * flag
             ENDDO

          ENDDO
       ENDDO
    ENDDO

    sums_l_l(nzt+1,:,tn) = sums_l_l(nzt,:,tn)   ! quasi boundary-condition for
                                                ! data output
!$OMP END PARALLEL

!
!-- Set vertical boundary values (Neumann conditions both at upward- and 
!-- downward facing walls. To set wall-boundary values, the surface data type 
!-- is applied.
!-- Horizontal boundary conditions at vertical walls are not set because
!-- so far vertical surfaces require usage of a Prandtl-layer where the boundary
!-- values of the diffusivities are not needed.
!-- Upward-facing
    !$OMP PARALLEL DO PRIVATE( i, j, k )
    DO  m = 1, bc_h(0)%ns
       i = bc_h(0)%i(m)            
       j = bc_h(0)%j(m)
       k = bc_h(0)%k(m)
       km(k-1,j,i) = km(k,j,i)
       kh(k-1,j,i) = kh(k,j,i)
    ENDDO
!
!-- Downward facing surfaces
    !$OMP PARALLEL DO PRIVATE( i, j, k )
    DO  m = 1, bc_h(1)%ns
       i = bc_h(1)%i(m)            
       j = bc_h(1)%j(m)
       k = bc_h(1)%k(m)
       km(k+1,j,i) = km(k,j,i)
       kh(k+1,j,i) = kh(k,j,i)
    ENDDO
!
!-- Model top
    !$OMP PARALLEL DO
    DO  i = nxlg, nxrg
       DO  j = nysg, nyng
          km(nzt+1,j,i) = km(nzt,j,i)
          kh(nzt+1,j,i) = kh(nzt,j,i)
       ENDDO
    ENDDO


!
!-- Set Neumann boundary conditions at the outflow boundaries in case of
!-- non-cyclic lateral boundaries
    IF ( outflow_l )  THEN
       km(:,:,nxl-1) = km(:,:,nxl)
       kh(:,:,nxl-1) = kh(:,:,nxl)
    ENDIF
    IF ( outflow_r )  THEN
       km(:,:,nxr+1) = km(:,:,nxr)
       kh(:,:,nxr+1) = kh(:,:,nxr)
    ENDIF
    IF ( outflow_s )  THEN
       km(:,nys-1,:) = km(:,nys,:)
       kh(:,nys-1,:) = kh(:,nys,:)
    ENDIF
    IF ( outflow_n )  THEN
       km(:,nyn+1,:) = km(:,nyn,:)
       kh(:,nyn+1,:) = kh(:,nyn,:)
    ENDIF
!
!-- Vertical nesting: set fine grid eddy viscosity top boundary condition
    IF ( vnest_init )  CALL vnest_boundary_conds_khkm

 END SUBROUTINE diffusivities