!> @file lpm_merging.f90 !------------------------------------------------------------------------------! ! This file is part of the PALM model system. ! ! 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 . ! ! Copyright 1997-2017 Leibniz Universitaet Hannover !------------------------------------------------------------------------------! ! ! Current revisions: ! ------------------ ! ! ! Former revisions: ! ----------------- ! $Id: lpm_merging.f90 2716 2017-12-29 16:35:59Z kanani $ ! Corrected "Former revisions" section ! ! ! Change in file header (GPL part) ! ! Added comments ! ! ! 2263 2017-06-08 14:59:01Z schwenkel ! Initial revision ! ! ! ! Description: ! ------------ ! This routine is a part of the Lagrangian particle model. Two Super droplets ! which fulfill certain criterion's (e.g. a big weighting factor and a small ! radius) can be merged into one super droplet with a increased number of ! represented particles of the super droplet. This mechanism ensures an ! improved a feasible amount of computational costs. The limits of particle ! creation should be chosen carefully! The idea of this algorithm is based on ! Unterstrasser and Soelch, 2014. !------------------------------------------------------------------------------! SUBROUTINE lpm_merging USE arrays_3d, & ONLY: ql USE cpulog, & ONLY: cpu_log, log_point_s USE indices, & ONLY: nxl, nxr, nyn, nys, nzb, nzt USE kinds USE particle_attributes, & ONLY: deleted_particles, grid_particles, initial_weighting_factor, & merge_drp, merging, number_of_particles, particles, prt_count, & radius_merge, sum_merge_drp, weight_factor_merge USE pegrid IMPLICIT NONE INTEGER(iwp) :: i !< INTEGER(iwp) :: j !< INTEGER(iwp) :: k !< INTEGER(iwp) :: n !< REAL(wp) :: ql_crit = 1.0E-5_wp !< threshold lwc for cloudy grid cells !< (e.g. Siebesma et al 2003, JAS, 60) CALL cpu_log( log_point_s(81), 'lpm_merging', 'start' ) merge_drp = 0 IF ( weight_factor_merge == -1.0_wp ) THEN weight_factor_merge = 0.5_wp * initial_weighting_factor ENDIF DO i = nxl, nxr DO j = nys, nyn DO k = nzb+1, nzt number_of_particles = prt_count(k,j,i) IF ( number_of_particles <= 0 .OR. & ql(k,j,i) >= ql_crit ) CYCLE particles => grid_particles(k,j,i)%particles(1:number_of_particles) ! !-- Start merging operations: This routine delete super droplets with !-- a small radius (radius <= radius_merge) and a low weighting !-- factor (weight_factor <= weight_factor_merge). The number of !-- represented particles will be added to the next particle of the !-- particle array. Tests showed that this simplified method can be !-- used because it will only take place outside of cloudy grid !-- boxes where ql <= 1.0E-5 kg/kg. Therefore, especially former cloned !-- and subsequent evaporated super droplets will be merged. DO n = 1, number_of_particles-1 IF ( particles(n)%particle_mask .AND. & particles(n+1)%particle_mask .AND. & particles(n)%radius <= radius_merge .AND. & particles(n)%weight_factor <= weight_factor_merge ) & THEN particles(n+1)%weight_factor = & particles(n+1)%weight_factor + & ( particles(n)%radius**3 / & particles(n+1)%radius**3 * & particles(n)%weight_factor & ) particles(n)%particle_mask = .FALSE. deleted_particles = deleted_particles + 1 merge_drp = merge_drp + 1 ENDIF ENDDO ENDDO ENDDO ENDDO sum_merge_drp = sum_merge_drp + merge_drp CALL cpu_log( log_point_s(81), 'lpm_merging', 'stop' ) END SUBROUTINE lpm_merging