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1! radiation_tripleclouds_lw.F90 - Longwave "Tripleclouds" solver
2!
3! (C) Copyright 2016- ECMWF.
4!
5! This software is licensed under the terms of the Apache Licence Version 2.0
6! which can be obtained at http://www.apache.org/licenses/LICENSE-2.0.
7!
8! In applying this licence, ECMWF does not waive the privileges and immunities
9! granted to it by virtue of its status as an intergovernmental organisation
10! nor does it submit to any jurisdiction.
11!
12! Author:  Robin Hogan
13! Email:   r.j.hogan@ecmwf.int
14!
15! Modifications
16!   2017-04-28  R. Hogan  Receive emission/albedo rather than planck/emissivity
17!   2017-04-22  R. Hogan  Store surface fluxes at all g-points
18!   2017-10-23  R. Hogan  Renamed single-character variables
19!   2018-10-08  R. Hogan  Call calc_region_properties
20!   2020-09-18  R. Hogan  Replaced some array expressions with loops
21!   2020-09-19  R. Hogan  Implement the cloud-only-scattering optimization
22
23module radiation_tripleclouds_lw
24
25  public
26
27contains
28  ! Small routine for scaling cloud optical depth in the cloudy
29  ! regions
30#include "radiation_optical_depth_scaling.h"
31
32  !---------------------------------------------------------------------
33  ! This module contains just one subroutine, the longwave
34  ! "Tripleclouds" solver in which cloud inhomogeneity is treated by
35  ! dividing each model level into three regions, one clear and two
36  ! cloudy (with differing optical depth). This approach was described
37  ! by Shonk and Hogan (2008).
38  subroutine solver_tripleclouds_lw(nlev,istartcol,iendcol, &
39       &  config, cloud, &
40       &  od, ssa, g, od_cloud, ssa_cloud, g_cloud, planck_hl, &
41       &  emission, albedo, &
42       &  flux)
43
44    use parkind1, only           : jprb
45    use yomhook,  only           : lhook, dr_hook
46
47!    use radiation_io, only             : nulout
48    use radiation_config, only         : config_type, IPdfShapeGamma
49    use radiation_cloud, only          : cloud_type
50    use radiation_regions, only        : calc_region_properties
51    use radiation_overlap, only        : calc_overlap_matrices
52    use radiation_flux, only           : flux_type, indexed_sum
53    use radiation_matrix, only         : singlemat_x_vec
54    use radiation_two_stream, only     : calc_two_stream_gammas_lw, &
55         &                               calc_reflectance_transmittance_lw, &
56         &                               calc_no_scattering_transmittance_lw
57    use radiation_adding_ica_lw, only  : adding_ica_lw, calc_fluxes_no_scattering_lw
58    use radiation_lw_derivatives, only : calc_lw_derivatives_region
59
60    implicit none
61
62    ! Inputs
63    integer, intent(in) :: nlev               ! number of model levels
64    integer, intent(in) :: istartcol, iendcol ! range of columns to process
65    type(config_type),        intent(in) :: config
66    type(cloud_type),         intent(in) :: cloud
67
68    ! Gas and aerosol optical depth of each layer at each longwave
69    ! g-point
70    real(jprb), intent(in), dimension(config%n_g_lw,nlev,istartcol:iendcol) :: od
71
72    ! Gas and aerosol single-scattering albedo and asymmetry factor,
73    ! only if longwave scattering by aerosols is to be represented
74    real(jprb), intent(in), &
75         &  dimension(config%n_g_lw_if_scattering,nlev,istartcol:iendcol) :: ssa, g
76
77    ! Cloud and precipitation optical depth of each layer in each
78    ! longwave band
79    real(jprb), intent(in) :: od_cloud(config%n_bands_lw,nlev,istartcol:iendcol)
80
81    ! Cloud and precipitation single-scattering albedo and asymmetry
82    ! factor, only if longwave scattering by clouds is to be
83    ! represented
84    real(jprb), intent(in), dimension(config%n_bands_lw_if_scattering, &
85         &                            nlev,istartcol:iendcol) :: ssa_cloud, g_cloud
86
87    ! Planck function (emitted flux from a black body) at half levels
88    ! and at the surface at each longwave g-point
89    real(jprb), intent(in), dimension(config%n_g_lw,nlev+1,istartcol:iendcol) :: planck_hl
90
91    ! Emission (Planck*emissivity) and albedo (1-emissivity) at the
92    ! surface at each longwave g-point
93    real(jprb), intent(in), dimension(config%n_g_lw, istartcol:iendcol) :: emission, albedo
94
95    ! Optical depth, single scattering albedo and asymmetry factor in
96    ! each g-point including gas, aerosol and clouds
97    real(jprb), dimension(config%n_g_lw) :: od_total, ssa_total, g_total
98
99    ! Modified optical depth after Tripleclouds scaling to represent
100    ! cloud inhomogeneity
101    real(jprb), dimension(config%n_g_lw) :: od_cloud_new
102
103    ! Output
104    type(flux_type), intent(inout):: flux
105
106    ! Local constants
107    integer, parameter :: nregions = 3
108
109    ! In a clear-sky layer this will be 1, otherwise equal to nregions
110    integer :: nreg
111
112    ! Local variables
113   
114    ! The area fractions of each region
115    real(jprb) :: region_fracs(1:nregions,nlev,istartcol:iendcol)
116
117    ! The scaling used for the optical depth in the cloudy regions
118    real(jprb) :: od_scaling(2:nregions,nlev,istartcol:iendcol)
119
120    ! Directional overlap matrices defined at all layer interfaces
121    ! including top-of-atmosphere and the surface
122    real(jprb), dimension(nregions,nregions,nlev+1, &
123         &                istartcol:iendcol) :: u_matrix, v_matrix
124
125    ! Two-stream variables
126    real(jprb), dimension(config%n_g_lw) :: gamma1, gamma2
127
128    ! Diffuse reflection and transmission matrices of each layer
129    real(jprb), dimension(config%n_g_lw, nregions, nlev) :: reflectance, transmittance
130
131    ! Emission by a layer into the upwelling or downwelling diffuse
132    ! streams
133    real(jprb), dimension(config%n_g_lw, nregions, nlev) &
134         &  :: source_up, source_dn
135
136    ! Clear-sky reflectance and transmittance
137    real(jprb), dimension(config%n_g_lw, nlev) &
138         &  :: ref_clear, trans_clear
139
140    ! ...clear-sky equivalent
141    real(jprb), dimension(config%n_g_lw, nlev) &
142         &  :: source_up_clear, source_dn_clear
143
144    ! Total albedo of the atmosphere/surface just above a layer
145    ! interface with respect to downwelling diffuse radiation at that
146    ! interface, where level index = 1 corresponds to the
147    ! top-of-atmosphere
148    real(jprb), dimension(config%n_g_lw, nregions, nlev+1) :: total_albedo
149
150    ! Upwelling radiation just above a layer interface due to emission
151    ! below that interface, where level index = 1 corresponds to the
152    ! top-of-atmosphere
153    real(jprb), dimension(config%n_g_lw, nregions, nlev+1) :: total_source
154
155    ! Total albedo and source of the atmosphere just below a layer interface
156    real(jprb), dimension(config%n_g_lw, nregions) &
157         &  :: total_albedo_below, total_source_below
158
159    ! Downwelling flux below and above an interface between
160    ! layers into a plane perpendicular to the direction of the sun
161    real(jprb), dimension(config%n_g_lw, nregions) &
162         &  :: flux_dn, flux_dn_below, flux_up
163
164    ! ...clear-sky equivalent (no distinction between "above/below")
165    real(jprb), dimension(config%n_g_lw, nlev+1) &
166         &  :: flux_dn_clear, flux_up_clear
167
168    ! Clear-sky equivalent, but actually its reciprocal to replace
169    ! some divisions by multiplications
170    real(jprb), dimension(config%n_g_lw, nregions) :: inv_denom
171
172    ! Identify clear-sky layers, with pseudo layers for outer space
173    ! and below the ground, both treated as single-region clear skies
174    logical :: is_clear_sky_layer(0:nlev+1)
175
176    ! Index of the highest cloudy layer
177    integer :: i_cloud_top
178
179    integer :: jcol, jlev, jg, jreg, jreg2, ng
180
181    real(jprb) :: hook_handle
182
183    if (lhook) call dr_hook('radiation_tripleclouds_lw:solver_tripleclouds_lw',0,hook_handle)
184
185    ! --------------------------------------------------------
186    ! Section 1: Prepare general variables and arrays
187    ! --------------------------------------------------------
188    ! Copy array dimensions to local variables for convenience
189    ng   = config%n_g_lw
190
191    ! Compute the wavelength-independent region fractions and
192    ! optical-depth scalings
193    call calc_region_properties(nlev,nregions,istartcol,iendcol, &
194         &  config%i_cloud_pdf_shape == IPdfShapeGamma, &
195         &  cloud%fraction, cloud%fractional_std, region_fracs, &
196         &  od_scaling, config%cloud_fraction_threshold)
197
198    ! Compute wavelength-independent overlap matrices u_matrix and v_matrix
199    call calc_overlap_matrices(nlev,nregions,istartcol,iendcol, &
200         &  region_fracs, cloud%overlap_param, &
201         &  u_matrix, v_matrix, &
202         &  decorrelation_scaling=config%cloud_inhom_decorr_scaling, &
203         &  cloud_fraction_threshold=config%cloud_fraction_threshold, &
204         &  use_beta_overlap=config%use_beta_overlap, &
205         &  cloud_cover=flux%cloud_cover_lw)
206
207    ! Main loop over columns
208    do jcol = istartcol, iendcol
209      ! --------------------------------------------------------
210      ! Section 2: Prepare column-specific variables and arrays
211      ! --------------------------------------------------------
212
213      ! Define which layers contain cloud; assume that
214      ! cloud%crop_cloud_fraction has already been called
215      is_clear_sky_layer = .true.
216      i_cloud_top = nlev+1
217      do jlev = 1,nlev
218        if (cloud%fraction(jcol,jlev) > 0.0_jprb) then
219          is_clear_sky_layer(jlev) = .false.
220          ! Get index to the first cloudy layer from the top
221          if (i_cloud_top > jlev) then
222            i_cloud_top = jlev
223          end if
224        end if
225      end do
226      if (config%do_lw_aerosol_scattering) then
227        ! This is actually the first layer in which we need to
228        ! consider scattering
229        i_cloud_top = 1
230      end if
231
232      ! --------------------------------------------------------
233      ! Section 3: Clear-sky calculation
234      ! --------------------------------------------------------
235
236      if (.not. config%do_lw_aerosol_scattering) then
237        ! No scattering in clear-sky flux calculation
238        do jlev = 1,nlev
239          ! Array-wise assignments
240          gamma1 = 0.0_jprb
241          gamma2 = 0.0_jprb
242          call calc_no_scattering_transmittance_lw(ng, od(:,jlev,jcol), &
243               &  planck_hl(:,jlev,jcol), planck_hl(:,jlev+1, jcol), &
244               &  trans_clear(:,jlev), source_up_clear(:,jlev), source_dn_clear(:,jlev))
245          ref_clear(:,jlev) = 0.0_jprb
246        end do
247        ! Simple down-then-up method to compute fluxes
248        call calc_fluxes_no_scattering_lw(ng, nlev, &
249             &  trans_clear, source_up_clear, source_dn_clear, &
250             &  emission(:,jcol), albedo(:,jcol), &
251             &  flux_up_clear, flux_dn_clear)
252      else
253        ! Scattering in clear-sky flux calculation
254        do jlev = 1,nlev
255          ! Array-wise assignments
256          gamma1 = 0.0_jprb
257          gamma2 = 0.0_jprb
258          call calc_two_stream_gammas_lw(ng, &
259               &  ssa(:,jlev,jcol), g(:,jlev,jcol), gamma1, gamma2)
260          call calc_reflectance_transmittance_lw(ng, &
261               &  od(:,jlev,jcol), gamma1, gamma2, &
262               &  planck_hl(:,jlev,jcol), planck_hl(:,jlev+1,jcol), &
263               &  ref_clear(:,jlev), trans_clear(:,jlev), &
264               &  source_up_clear(:,jlev), source_dn_clear(:,jlev))
265        end do
266        ! Use adding method to compute fluxes
267        call adding_ica_lw(ng, nlev, &
268             &  ref_clear, trans_clear, source_up_clear, source_dn_clear, &
269             &  emission(:,jcol), albedo(:,jcol), &
270             &  flux_up_clear, flux_dn_clear)
271      end if
272
273      if (config%do_clear) then
274        ! Sum over g-points to compute broadband fluxes
275        flux%lw_up_clear(jcol,:) = sum(flux_up_clear,1)
276        flux%lw_dn_clear(jcol,:) = sum(flux_dn_clear,1)
277        ! Store surface spectral downwelling fluxes
278        flux%lw_dn_surf_clear_g(:,jcol) = flux_dn_clear(:,nlev+1)
279        ! Save the spectral fluxes if required
280        if (config%do_save_spectral_flux) then
281          do jlev = 1,nlev+1
282            call indexed_sum(flux_up_clear(:,jlev), &
283                 &           config%i_spec_from_reordered_g_lw, &
284                 &           flux%lw_up_clear_band(:,jcol,jlev))
285            call indexed_sum(flux_dn_clear(:,jlev), &
286                 &           config%i_spec_from_reordered_g_lw, &
287                 &           flux%lw_dn_clear_band(:,jcol,jlev))
288          end do
289        end if
290      end if
291
292      ! --------------------------------------------------------
293      ! Section 4: Loop over cloudy layers to compute reflectance and transmittance
294      ! --------------------------------------------------------
295      ! In this section the reflectance, transmittance and sources
296      ! are computed for each layer
297     
298      ! Firstly, ensure clear-sky transmittance is valid for whole
299      ! depth of the atmosphere, because even above cloud it is used
300      ! by the LW derivatives
301      transmittance(:,1,:) = trans_clear(:,:)
302      ! Dummy values in cloudy regions above cloud top
303      if (i_cloud_top > 0) then
304        transmittance(:,2:,1:min(i_cloud_top,nlev)) = 1.0_jprb
305      end if
306
307      do jlev = i_cloud_top,nlev ! Start at cloud top and work down
308
309        ! Array-wise assignments
310        gamma1 = 0.0_jprb
311        gamma2 = 0.0_jprb
312
313        ! Copy over clear-sky properties
314        reflectance(:,1,jlev)    = ref_clear(:,jlev)
315        source_up(:,1,jlev)      = source_up_clear(:,jlev) ! Scaled later by region size
316        source_dn(:,1,jlev)      = source_dn_clear(:,jlev) ! Scaled later by region size
317        nreg = nregions
318        if (is_clear_sky_layer(jlev)) then
319          nreg = 1
320          reflectance(:,2:,jlev)   = 0.0_jprb
321          transmittance(:,2:,jlev) = 1.0_jprb
322          source_up(:,2:,jlev)     = 0.0_jprb
323          source_dn(:,2:,jlev)     = 0.0_jprb
324        else
325          do jreg = 2,nreg
326            ! Cloudy sky
327            ! Add scaled cloud optical depth to clear-sky value
328            od_cloud_new = od_cloud(config%i_band_from_reordered_g_lw,jlev,jcol) &
329                 &       * od_scaling(jreg,jlev,jcol)
330            od_total = od(:,jlev,jcol) + od_cloud_new
331
332            if (config%do_lw_cloud_scattering) then
333              ssa_total = 0.0_jprb
334              g_total   = 0.0_jprb             
335              if (config%do_lw_aerosol_scattering) then
336                where (od_total > 0.0_jprb)
337                  ssa_total = (ssa(:,jlev,jcol)*od(:,jlev,jcol) &
338                       &     + ssa_cloud(config%i_band_from_reordered_g_lw,jlev,jcol) &
339                       &     *  od_cloud_new) &
340                       &     / od_total
341                end where
342                where (ssa_total > 0.0_jprb .and. od_total > 0.0_jprb)
343                  g_total = (g(:,jlev,jcol)*ssa(:,jlev,jcol)*od(:,jlev,jcol) &
344                       &     +   g_cloud(config%i_band_from_reordered_g_lw,jlev,jcol) &
345                       &     * ssa_cloud(config%i_band_from_reordered_g_lw,jlev,jcol) &
346                       &     *  od_cloud_new) &
347                       &     / (ssa_total*od_total)
348                end where
349              else
350                where (od_total > 0.0_jprb)
351                  ssa_total = ssa_cloud(config%i_band_from_reordered_g_lw,jlev,jcol) &
352                       &     * od_cloud_new / od_total
353                end where
354                where (ssa_total > 0.0_jprb .and. od_total > 0.0_jprb)
355                  g_total = g_cloud(config%i_band_from_reordered_g_lw,jlev,jcol) &
356                       &     * ssa_cloud(config%i_band_from_reordered_g_lw,jlev,jcol) &
357                       &     *  od_cloud_new / (ssa_total*od_total)
358                end where
359              end if
360              call calc_two_stream_gammas_lw(ng, &
361                   &  ssa_total, g_total, gamma1, gamma2)
362              call calc_reflectance_transmittance_lw(ng, &
363                   &  od_total, gamma1, gamma2, &
364                   &  planck_hl(:,jlev,jcol), planck_hl(:,jlev+1,jcol), &
365                   &  reflectance(:,jreg,jlev), transmittance(:,jreg,jlev), &
366                   &  source_up(:,jreg,jlev), source_dn(:,jreg,jlev))
367            else
368              ! No-scattering case: use simpler functions for
369              ! transmission and emission
370              call calc_no_scattering_transmittance_lw(ng, od_total, &
371                   &  planck_hl(:,jlev,jcol), planck_hl(:,jlev+1, jcol), &
372                   &  transmittance(:,jreg,jlev), source_up(:,jreg,jlev), source_dn(:,jreg,jlev))
373              reflectance(:,jreg,jlev) = 0.0_jprb
374            end if
375          end do
376          ! Emission is scaled by the size of each region
377          do jreg = 1,nregions
378            source_up(:,jreg,jlev) = region_fracs(jreg,jlev,jcol) * source_up(:,jreg,jlev)
379            source_dn(:,jreg,jlev) = region_fracs(jreg,jlev,jcol) * source_dn(:,jreg,jlev)
380          end do
381        end if
382
383      end do ! Loop over levels
384
385      ! --------------------------------------------------------
386      ! Section 5: Compute total sources and albedos at each half level
387      ! --------------------------------------------------------
388
389      total_albedo(:,:,:) = 0.0_jprb
390      total_source(:,:,:) = 0.0_jprb
391
392      ! Calculate the upwelling radiation emitted by the surface, and
393      ! copy the surface albedo into total_albedo
394      do jreg = 1,nregions
395        do jg = 1,ng
396          ! region_fracs(jreg,nlev,jcol) is the fraction of each region in the
397          ! lowest model level
398          total_source(jg,jreg,nlev+1) = region_fracs(jreg,nlev,jcol)*emission(jg,jcol)
399          total_albedo(jg,jreg,nlev+1) = albedo(jg,jcol)
400        end do
401      end do
402
403      ! Work up from the surface computing the total albedo of the
404      ! atmosphere and the total upwelling due to emission below each
405      ! level below using the adding method
406      do jlev = nlev,i_cloud_top,-1
407
408        total_albedo_below        = 0.0_jprb
409
410        if (is_clear_sky_layer(jlev)) then
411          total_albedo_below = 0.0_jprb
412          total_source_below = 0.0_jprb
413          do jg = 1,ng
414            inv_denom(jg,1) = 1.0_jprb &
415                 &  / (1.0_jprb - total_albedo(jg,1,jlev+1)*reflectance(jg,1,jlev))
416            total_albedo_below(jg,1) = reflectance(jg,1,jlev) &
417                 &  + transmittance(jg,1,jlev)*transmittance(jg,1,jlev)*total_albedo(jg,1,jlev+1) &
418                 &  * inv_denom(jg,1)
419            total_source_below(jg,1) = source_up(jg,1,jlev) &
420                 &  + transmittance(jg,1,jlev)*(total_source(jg,1,jlev+1) &
421                 &  + total_albedo(jg,1,jlev+1)*source_dn(jg,1,jlev)) &
422                 &  * inv_denom(jg,1)
423          end do
424        else
425          inv_denom = 1.0_jprb / (1.0_jprb - total_albedo(:,:,jlev+1)*reflectance(:,:,jlev))
426          total_albedo_below = reflectance(:,:,jlev) &
427               &  + transmittance(:,:,jlev)*transmittance(:,:,jlev)*total_albedo(:,:,jlev+1) &
428               &  * inv_denom
429          total_source_below = source_up(:,:,jlev) &
430               &  + transmittance(:,:,jlev)*(total_source(:,:,jlev+1) &
431               &  + total_albedo(:,:,jlev+1)*source_dn(:,:,jlev)) &
432               &  * inv_denom
433        end if
434
435        ! Account for cloud overlap when converting albedo below a
436        ! layer interface to the equivalent values just above
437        if (is_clear_sky_layer(jlev) .and. is_clear_sky_layer(jlev-1)) then
438          total_albedo(:,:,jlev) = total_albedo_below(:,:)
439          total_source(:,:,jlev) = total_source_below(:,:)
440        else
441          total_source(:,:,jlev) = singlemat_x_vec(ng,ng,nregions,&
442               &  u_matrix(:,:,jlev,jcol), total_source_below)
443          ! Use overlap matrix and exclude "anomalous" horizontal
444          ! transport described by Shonk & Hogan (2008).  Therefore,
445          ! the operation we perform is essentially diag(total_albedo)
446          ! = matmul(transpose(v_matrix), diag(total_albedo_below)).
447          do jreg = 1,nregions
448            do jreg2 = 1,nregions
449              total_albedo(:,jreg,jlev) &
450                   &  = total_albedo(:,jreg,jlev) &
451                   &  + total_albedo_below(:,jreg2) &
452                   &  * v_matrix(jreg2,jreg,jlev,jcol)
453
454            end do
455          end do
456
457        end if
458       
459      end do ! Reverse loop over levels
460
461      ! --------------------------------------------------------
462      ! Section 6: Copy over downwelling fluxes above cloud top
463      ! --------------------------------------------------------
464      do jlev = 1,i_cloud_top
465        if (config%do_clear) then
466          ! Clear-sky fluxes have already been averaged: use these
467          flux%lw_dn(jcol,jlev) = flux%lw_dn_clear(jcol,jlev)
468          if (config%do_save_spectral_flux) then
469            flux%lw_dn_band(:,jcol,jlev) = flux%lw_dn_clear_band(:,jcol,jlev)
470          end if
471        else
472          flux%lw_dn(jcol,:) = sum(flux_dn_clear(:,jlev))
473          if (config%do_save_spectral_flux) then
474            call indexed_sum(flux_dn_clear(:,jlev), &
475                 &           config%i_spec_from_reordered_g_lw, &
476                 &           flux%lw_dn_band(:,jcol,jlev))
477          end if
478        end if
479      end do
480
481      ! --------------------------------------------------------
482      ! Section 7: Compute fluxes up to top-of-atmosphere
483      ! --------------------------------------------------------
484
485      ! Compute the fluxes just above the highest cloud
486      flux_up(:,1) = total_source(:,1,i_cloud_top) &
487           &  + total_albedo(:,1,i_cloud_top)*flux_dn_clear(:,i_cloud_top)
488      flux_up(:,2:) = 0.0_jprb
489      flux%lw_up(jcol,i_cloud_top) = sum(flux_up(:,1))
490      if (config%do_save_spectral_flux) then
491        call indexed_sum(flux_up(:,1), &
492             &           config%i_spec_from_reordered_g_lw, &
493             &           flux%lw_up_band(:,jcol,i_cloud_top))
494      end if
495      do jlev = i_cloud_top-1,1,-1
496        flux_up(:,1) = trans_clear(:,jlev)*flux_up(:,1) + source_up_clear(:,jlev)
497        flux%lw_up(jcol,jlev) = sum(flux_up(:,1))
498        if (config%do_save_spectral_flux) then
499          call indexed_sum(flux_up(:,1), &
500               &           config%i_spec_from_reordered_g_lw, &
501               &           flux%lw_up_band(:,jcol,jlev))
502        end if
503      end do
504
505      ! --------------------------------------------------------
506      ! Section 8: Compute fluxes down to surface
507      ! --------------------------------------------------------
508
509      ! Copy over downwelling spectral fluxes at top of first
510      ! scattering layer, using overlap matrix to translate to the
511      ! regions of the first layer of cloud
512      do jreg = 1,nregions
513        flux_dn(:,jreg)  = v_matrix(jreg,1,i_cloud_top,jcol)*flux_dn_clear(:,i_cloud_top)
514      end do
515
516      ! Final loop back down through the atmosphere to compute fluxes
517      do jlev = i_cloud_top,nlev
518
519        if (is_clear_sky_layer(jlev)) then
520          do jg = 1,ng
521            flux_dn(jg,1) = (transmittance(jg,1,jlev)*flux_dn(jg,1) &
522                 &  + reflectance(jg,1,jlev)*total_source(jg,1,jlev+1) + source_dn(jg,1,jlev) ) &
523                 &  / (1.0_jprb - reflectance(jg,1,jlev)*total_albedo(jg,1,jlev+1))
524            flux_up(jg,1) = total_source(jg,1,jlev+1) + flux_dn(jg,1)*total_albedo(jg,1,jlev+1)
525          end do
526          flux_dn(:,2:)  = 0.0_jprb
527          flux_up(:,2:)  = 0.0_jprb
528        else
529          flux_dn = (transmittance(:,:,jlev)*flux_dn &
530               &     + reflectance(:,:,jlev)*total_source(:,:,jlev+1) + source_dn(:,:,jlev) ) &
531               &  / (1.0_jprb - reflectance(:,:,jlev)*total_albedo(:,:,jlev+1))
532          flux_up = total_source(:,:,jlev+1) + flux_dn*total_albedo(:,:,jlev+1)
533        end if
534
535        if (.not. (is_clear_sky_layer(jlev) &
536             &    .and. is_clear_sky_layer(jlev+1))) then
537          ! Account for overlap rules in translating fluxes just above
538          ! a layer interface to the values just below
539          flux_dn_below = singlemat_x_vec(ng,ng,nregions, &
540               &  v_matrix(:,:,jlev+1,jcol), flux_dn)
541          flux_dn = flux_dn_below
542        end if ! Otherwise the fluxes in each region are the same so
543               ! nothing to do
544
545        ! Store the broadband fluxes
546        flux%lw_up(jcol,jlev+1) = sum(sum(flux_up,1))
547        flux%lw_dn(jcol,jlev+1) = sum(sum(flux_dn,1))
548
549        ! Save the spectral fluxes if required
550        if (config%do_save_spectral_flux) then
551          call indexed_sum(sum(flux_up,2), &
552               &           config%i_spec_from_reordered_g_lw, &
553               &           flux%lw_up_band(:,jcol,jlev+1))
554          call indexed_sum(sum(flux_dn,2), &
555               &           config%i_spec_from_reordered_g_lw, &
556               &           flux%lw_dn_band(:,jcol,jlev+1))
557         end if
558
559      end do ! Final loop over levels
560     
561      ! Store surface spectral downwelling fluxes, which at this point
562      ! are at the surface
563      flux%lw_dn_surf_g(:,jcol) = sum(flux_dn,2)
564
565      ! Compute the longwave derivatives needed by Hogan and Bozzo
566      ! (2015) approximate radiation update scheme
567      if (config%do_lw_derivatives) then
568        ! Note that at this point flux_up contains the spectral
569        ! fluxes into the regions of the lowest layer; we sum over
570        ! regions first to provide a simple spectral flux upwelling
571        ! from the surface
572        call calc_lw_derivatives_region(ng, nlev, nregions, jcol, transmittance, &
573             &  u_matrix(:,:,:,jcol), sum(flux_up,2), flux%lw_derivatives)
574      end if
575
576    end do ! Loop over columns
577
578    if (lhook) call dr_hook('radiation_tripleclouds_lw:solver_tripleclouds_lw',1,hook_handle)
579
580  end subroutine solver_tripleclouds_lw
581
582end module radiation_tripleclouds_lw
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