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source: palm/trunk/SOURCE/diffusion_u.f90 @ 2639

Last change on this file since 2639 was 2638, checked in by raasch, 7 years ago
bugfix for cases with constant top momentumflux
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File size: 24.7 KB

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1	!> @file diffusion_u.f90
2	!------------------------------------------------------------------------------!
3	! This file is part of PALM.
4	!
5	! PALM is free software: you can redistribute it and/or modify it under the
6	! terms of the GNU General Public License as published by the Free Software
7	! Foundation, either version 3 of the License, or (at your option) any later
8	! version.
9	!
10	! PALM is distributed in the hope that it will be useful, but WITHOUT ANY
11	! WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
12	! A PARTICULAR PURPOSE. See the GNU General Public License for more details.
13	!
14	! You should have received a copy of the GNU General Public License along with
15	! PALM. If not, see <http://www.gnu.org/licenses/>.
16	!
17	! Copyright 1997-2017 Leibniz Universitaet Hannover
18	!------------------------------------------------------------------------------!
19	!
20	! Current revisions:
21	! -----------------
22	!
23	!
24	! Former revisions:
25	! -----------------
26	! $Id: diffusion_u.f90 2638 2017-11-23 12:44:23Z raasch $
27	! bugfix for constant top momentumflux
28	!
29	! 2233 2017-05-30 18:08:54Z suehring
30	!
31	! 2232 2017-05-30 17:47:52Z suehring
32	! Adjustments to new topography and surface concept
33	!
34	! 2118 2017-01-17 16:38:49Z raasch
35	! OpenACC version of subroutine removed
36	!
37	! 2037 2016-10-26 11:15:40Z knoop
38	! Anelastic approximation implemented
39	!
40	! 2000 2016-08-20 18:09:15Z knoop
41	! Forced header and separation lines into 80 columns
42	!
43	! 1873 2016-04-18 14:50:06Z maronga
44	! Module renamed (removed _mod)
45	!
46	! 1850 2016-04-08 13:29:27Z maronga
47	! Module renamed
48	!
49	! 1740 2016-01-13 08:19:40Z raasch
50	! unnecessary calculations of kmzm and kmzp in wall bounded parts removed
51	!
52	! 1691 2015-10-26 16:17:44Z maronga
53	! Formatting corrections.
54	!
55	! 1682 2015-10-07 23:56:08Z knoop
56	! Code annotations made doxygen readable
57	!
58	! 1340 2014-03-25 19:45:13Z kanani
59	! REAL constants defined as wp-kind
60	!
61	! 1320 2014-03-20 08:40:49Z raasch
62	! ONLY-attribute added to USE-statements,
63	! kind-parameters added to all INTEGER and REAL declaration statements,
64	! kinds are defined in new module kinds,
65	! revision history before 2012 removed,
66	! comment fields (!:) to be used for variable explanations added to
67	! all variable declaration statements
68	!
69	! 1257 2013-11-08 15:18:40Z raasch
70	! openacc loop and loop vector clauses removed, declare create moved after
71	! the FORTRAN declaration statement
72	!
73	! 1128 2013-04-12 06:19:32Z raasch
74	! loop index bounds in accelerator version replaced by i_left, i_right, j_south,
75	! j_north
76	!
77	! 1036 2012-10-22 13:43:42Z raasch
78	! code put under GPL (PALM 3.9)
79	!
80	! 1015 2012-09-27 09:23:24Z raasch
81	! accelerator version (*_acc) added
82	!
83	! 1001 2012-09-13 14:08:46Z raasch
84	! arrays comunicated by module instead of parameter list
85	!
86	! 978 2012-08-09 08:28:32Z fricke
87	! outflow damping layer removed
88	! kmym_x/_y and kmyp_x/_y change to kmym and kmyp
89	!
90	! Revision 1.1 1997/09/12 06:23:51 raasch
91	! Initial revision
92	!
93	!
94	! Description:
95	! ------------
96	!> Diffusion term of the u-component
97	!> @todo additional damping (needed for non-cyclic bc) causes bad vectorization
98	!> and slows down the speed on NEC about 5-10%
99	!------------------------------------------------------------------------------!
100	MODULE diffusion_u_mod
101
102
103	PRIVATE
104	PUBLIC diffusion_u
105
106	INTERFACE diffusion_u
107	MODULE PROCEDURE diffusion_u
108	MODULE PROCEDURE diffusion_u_ij
109	END INTERFACE diffusion_u
110
111	CONTAINS
112
113
114	!------------------------------------------------------------------------------!
115	! Description:
116	! ------------
117	!> Call for all grid points
118	!------------------------------------------------------------------------------!
119	SUBROUTINE diffusion_u
120
121	USE arrays_3d, &
122	ONLY: ddzu, ddzw, km, tend, u, v, w, drho_air, rho_air_zw
123
124	USE control_parameters, &
125	ONLY: constant_top_momentumflux, use_surface_fluxes, &
126	use_top_fluxes
127
128	USE grid_variables, &
129	ONLY: ddx, ddx2, ddy
130
131	USE indices, &
132	ONLY: nxl, nxlu, nxr, nyn, nys, nzb, nzt, wall_flags_0
133
134	USE kinds
135
136	USE surface_mod, &
137	ONLY : surf_def_h, surf_def_v, surf_lsm_h, surf_lsm_v, surf_usm_h, &
138	surf_usm_v
139
140	IMPLICIT NONE
141
142	INTEGER(iwp) :: i !< running index x direction
143	INTEGER(iwp) :: j !< running index y direction
144	INTEGER(iwp) :: k !< running index z direction
145	INTEGER(iwp) :: l !< running index of surface type, south- or north-facing wall
146	INTEGER(iwp) :: m !< running index surface elements
147	INTEGER(iwp) :: surf_e !< End index of surface elements at (j,i)-gridpoint
148	INTEGER(iwp) :: surf_s !< Start index of surface elements at (j,i)-gridpoint
149
150	REAL(wp) :: flag !< flag to mask topography grid points
151	REAL(wp) :: kmym !<
152	REAL(wp) :: kmyp !<
153	REAL(wp) :: kmzm !<
154	REAL(wp) :: kmzp !<
155	REAL(wp) :: mask_bottom !< flag to mask vertical upward-facing surface
156	REAL(wp) :: mask_north !< flag to mask vertical surface north of the grid point
157	REAL(wp) :: mask_south !< flag to mask vertical surface south of the grid point
158	REAL(wp) :: mask_top !< flag to mask vertical downward-facing surface
159
160
161
162	DO i = nxlu, nxr
163	DO j = nys, nyn
164	!
165	!-- Compute horizontal diffusion
166	DO k = nzb+1, nzt
167	!
168	!-- Predetermine flag to mask topography and wall-bounded grid points.
169	!-- It is sufficient to masked only north- and south-facing surfaces, which
170	!-- need special treatment for the u-component.
171	flag = MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j,i), 1 ) )
172	mask_south = MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j-1,i), 1 ) )
173	mask_north = MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j+1,i), 1 ) )
174	!
175	!-- Interpolate eddy diffusivities on staggered gridpoints
176	kmyp = 0.25_wp * &
177	( km(k,j,i)+km(k,j+1,i)+km(k,j,i-1)+km(k,j+1,i-1) )
178	kmym = 0.25_wp * &
179	( km(k,j,i)+km(k,j-1,i)+km(k,j,i-1)+km(k,j-1,i-1) )
180
181	tend(k,j,i) = tend(k,j,i) &
182	+ 2.0_wp * ( &
183	km(k,j,i) * ( u(k,j,i+1) - u(k,j,i) ) &
184	- km(k,j,i-1) * ( u(k,j,i) - u(k,j,i-1) ) &
185	) * ddx2 * flag &
186	+ ( mask_north * ( &
187	kmyp * ( u(k,j+1,i) - u(k,j,i) ) * ddy &
188	+ kmyp * ( v(k,j+1,i) - v(k,j+1,i-1) ) * ddx &
189	) &
190	- mask_south * ( &
191	kmym * ( u(k,j,i) - u(k,j-1,i) ) * ddy &
192	+ kmym * ( v(k,j,i) - v(k,j,i-1) ) * ddx &
193	) &
194	) * ddy * flag
195	ENDDO
196	!
197	!-- Add horizontal momentum flux u'v' at north- (l=0) and south-facing (l=1)
198	!-- surfaces. Note, in the the flat case, loops won't be entered as
199	!-- start_index > end_index. Furtermore, note, no vertical natural surfaces
200	!-- so far.
201	!-- Default-type surfaces
202	DO l = 0, 1
203	surf_s = surf_def_v(l)%start_index(j,i)
204	surf_e = surf_def_v(l)%end_index(j,i)
205	DO m = surf_s, surf_e
206	k = surf_def_v(l)%k(m)
207	tend(k,j,i) = tend(k,j,i) + &
208	surf_def_v(l)%mom_flux_uv(m) * ddy
209	ENDDO
210	ENDDO
211	!
212	!-- Natural-type surfaces
213	DO l = 0, 1
214	surf_s = surf_lsm_v(l)%start_index(j,i)
215	surf_e = surf_lsm_v(l)%end_index(j,i)
216	DO m = surf_s, surf_e
217	k = surf_lsm_v(l)%k(m)
218	tend(k,j,i) = tend(k,j,i) + &
219	surf_lsm_v(l)%mom_flux_uv(m) * ddy
220	ENDDO
221	ENDDO
222	!
223	!-- Urban-type surfaces
224	DO l = 0, 1
225	surf_s = surf_usm_v(l)%start_index(j,i)
226	surf_e = surf_usm_v(l)%end_index(j,i)
227	DO m = surf_s, surf_e
228	k = surf_usm_v(l)%k(m)
229	tend(k,j,i) = tend(k,j,i) + &
230	surf_usm_v(l)%mom_flux_uv(m) * ddy
231	ENDDO
232	ENDDO
233
234	!
235	!-- Compute vertical diffusion. In case of simulating a surface layer,
236	!-- respective grid diffusive fluxes are masked (flag 8) within this
237	!-- loop, and added further below, else, simple gradient approach is
238	!-- applied. Model top is also mask if top-momentum flux is given.
239	DO k = nzb+1, nzt
240	!
241	!-- Determine flags to mask topography below and above. Flag 1 is
242	!-- used to mask topography in general, and flag 8 implies
243	!-- information about use_surface_fluxes. Flag 9 is used to control
244	!-- momentum flux at model top.
245	mask_bottom = MERGE( 1.0_wp, 0.0_wp, &
246	BTEST( wall_flags_0(k-1,j,i), 8 ) )
247	mask_top = MERGE( 1.0_wp, 0.0_wp, &
248	BTEST( wall_flags_0(k+1,j,i), 8 ) ) * &
249	MERGE( 1.0_wp, 0.0_wp, &
250	BTEST( wall_flags_0(k+1,j,i), 9 ) )
251	flag = MERGE( 1.0_wp, 0.0_wp, &
252	BTEST( wall_flags_0(k,j,i), 1 ) )
253	!
254	!-- Interpolate eddy diffusivities on staggered gridpoints
255	kmzp = 0.25_wp * &
256	( km(k,j,i)+km(k+1,j,i)+km(k,j,i-1)+km(k+1,j,i-1) )
257	kmzm = 0.25_wp * &
258	( km(k,j,i)+km(k-1,j,i)+km(k,j,i-1)+km(k-1,j,i-1) )
259
260	tend(k,j,i) = tend(k,j,i) &
261	+ ( kmzp * ( ( u(k+1,j,i) - u(k,j,i) ) * ddzu(k+1) &
262	+ ( w(k,j,i) - w(k,j,i-1) ) * ddx &
263	) * rho_air_zw(k) * mask_top &
264	- kmzm * ( ( u(k,j,i) - u(k-1,j,i) ) * ddzu(k) &
265	+ ( w(k-1,j,i) - w(k-1,j,i-1) ) * ddx &
266	) * rho_air_zw(k-1) * mask_bottom &
267	) * ddzw(k) * drho_air(k) * flag
268	ENDDO
269
270	!
271	!-- Vertical diffusion at the first grid point above the surface,
272	!-- if the momentum flux at the bottom is given by the Prandtl law or
273	!-- if it is prescribed by the user.
274	!-- Difference quotient of the momentum flux is not formed over half
275	!-- of the grid spacing (2.0*ddzw(k)) any more, since the comparison
276	!-- with other (LES) models showed that the values of the momentum
277	!-- flux becomes too large in this case.
278	!-- The term containing w(k-1,..) (see above equation) is removed here
279	!-- because the vertical velocity is assumed to be zero at the surface.
280	IF ( use_surface_fluxes ) THEN
281	!
282	!-- Default-type surfaces, upward-facing
283	surf_s = surf_def_h(0)%start_index(j,i)
284	surf_e = surf_def_h(0)%end_index(j,i)
285	DO m = surf_s, surf_e
286
287	k = surf_def_h(0)%k(m)
288
289	tend(k,j,i) = tend(k,j,i) &
290	+ ( - ( - surf_def_h(0)%usws(m) ) &
291	) * ddzw(k) * drho_air(k)
292	ENDDO
293	!
294	!-- Default-type surfaces, dowward-facing
295	surf_s = surf_def_h(1)%start_index(j,i)
296	surf_e = surf_def_h(1)%end_index(j,i)
297	DO m = surf_s, surf_e
298
299	k = surf_def_h(1)%k(m)
300
301	tend(k,j,i) = tend(k,j,i) &
302	+ ( - surf_def_h(1)%usws(m) &
303	) * ddzw(k) * drho_air(k)
304	ENDDO
305	!
306	!-- Natural-type surfaces, upward-facing
307	surf_s = surf_lsm_h%start_index(j,i)
308	surf_e = surf_lsm_h%end_index(j,i)
309	DO m = surf_s, surf_e
310
311	k = surf_lsm_h%k(m)
312
313	tend(k,j,i) = tend(k,j,i) &
314	+ ( - ( - surf_lsm_h%usws(m) ) &
315	) * ddzw(k) * drho_air(k)
316	ENDDO
317	!
318	!-- Urban-type surfaces, upward-facing
319	surf_s = surf_usm_h%start_index(j,i)
320	surf_e = surf_usm_h%end_index(j,i)
321	DO m = surf_s, surf_e
322
323	k = surf_usm_h%k(m)
324
325	tend(k,j,i) = tend(k,j,i) &
326	+ ( - ( - surf_usm_h%usws(m) ) &
327	) * ddzw(k) * drho_air(k)
328	ENDDO
329
330	ENDIF
331	!
332	!-- Add momentum flux at model top
333	IF ( use_top_fluxes .AND. constant_top_momentumflux ) THEN
334	surf_s = surf_def_h(2)%start_index(j,i)
335	surf_e = surf_def_h(2)%end_index(j,i)
336	DO m = surf_s, surf_e
337
338	k = surf_def_h(2)%k(m)
339
340	tend(k,j,i) = tend(k,j,i) &
341	+ ( - surf_def_h(2)%usws(m) ) * ddzw(k) * drho_air(k)
342	ENDDO
343	ENDIF
344
345	ENDDO
346	ENDDO
347
348	END SUBROUTINE diffusion_u
349
350
351	!------------------------------------------------------------------------------!
352	! Description:
353	! ------------
354	!> Call for grid point i,j
355	!------------------------------------------------------------------------------!
356	SUBROUTINE diffusion_u_ij( i, j )
357
358	USE arrays_3d, &
359	ONLY: ddzu, ddzw, km, tend, u, v, w, drho_air, rho_air_zw
360
361	USE control_parameters, &
362	ONLY: constant_top_momentumflux, use_surface_fluxes, &
363	use_top_fluxes
364
365	USE grid_variables, &
366	ONLY: ddx, ddx2, ddy
367
368	USE indices, &
369	ONLY: nzb, nzt, wall_flags_0
370
371	USE kinds
372
373	USE surface_mod, &
374	ONLY : surf_def_h, surf_def_v, surf_lsm_h, surf_lsm_v, surf_usm_h, &
375	surf_usm_v
376
377	IMPLICIT NONE
378
379	INTEGER(iwp) :: i !< running index x direction
380	INTEGER(iwp) :: j !< running index y direction
381	INTEGER(iwp) :: k !< running index z direction
382	INTEGER(iwp) :: l !< running index of surface type, south- or north-facing wall
383	INTEGER(iwp) :: m !< running index surface elements
384	INTEGER(iwp) :: surf_e !< End index of surface elements at (j,i)-gridpoint
385	INTEGER(iwp) :: surf_s !< Start index of surface elements at (j,i)-gridpoint
386
387	REAL(wp) :: flag !< flag to mask topography grid points
388	REAL(wp) :: kmym !<
389	REAL(wp) :: kmyp !<
390	REAL(wp) :: kmzm !<
391	REAL(wp) :: kmzp !<
392	REAL(wp) :: mask_bottom !< flag to mask vertical upward-facing surface
393	REAL(wp) :: mask_north !< flag to mask vertical surface north of the grid point
394	REAL(wp) :: mask_south !< flag to mask vertical surface south of the grid point
395	REAL(wp) :: mask_top !< flag to mask vertical downward-facing surface
396	!
397	!-- Compute horizontal diffusion
398	DO k = nzb+1, nzt
399	!
400	!-- Predetermine flag to mask topography and wall-bounded grid points.
401	!-- It is sufficient to masked only north- and south-facing surfaces, which
402	!-- need special treatment for the u-component.
403	flag = MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j,i), 1 ) )
404	mask_south = MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j-1,i), 1 ) )
405	mask_north = MERGE( 1.0_wp, 0.0_wp, BTEST( wall_flags_0(k,j+1,i), 1 ) )
406	!
407	!-- Interpolate eddy diffusivities on staggered gridpoints
408	kmyp = 0.25_wp * ( km(k,j,i)+km(k,j+1,i)+km(k,j,i-1)+km(k,j+1,i-1) )
409	kmym = 0.25_wp * ( km(k,j,i)+km(k,j-1,i)+km(k,j,i-1)+km(k,j-1,i-1) )
410
411	tend(k,j,i) = tend(k,j,i) &
412	+ 2.0_wp * ( &
413	km(k,j,i) * ( u(k,j,i+1) - u(k,j,i) ) &
414	- km(k,j,i-1) * ( u(k,j,i) - u(k,j,i-1) ) &
415	) * ddx2 * flag &
416	+ ( &
417	mask_north * kmyp * ( ( u(k,j+1,i) - u(k,j,i) ) * ddy &
418	+ ( v(k,j+1,i) - v(k,j+1,i-1) ) * ddx &
419	) &
420	- mask_south * kmym * ( ( u(k,j,i) - u(k,j-1,i) ) * ddy &
421	+ ( v(k,j,i) - v(k,j,i-1) ) * ddx &
422	) &
423	) * ddy * flag
424	ENDDO
425
426	!
427	!-- Add horizontal momentum flux u'v' at north- (l=0) and south-facing (l=1)
428	!-- surfaces. Note, in the the flat case, loops won't be entered as
429	!-- start_index > end_index. Furtermore, note, no vertical natural surfaces
430	!-- so far.
431	!-- Default-type surfaces
432	DO l = 0, 1
433	surf_s = surf_def_v(l)%start_index(j,i)
434	surf_e = surf_def_v(l)%end_index(j,i)
435	DO m = surf_s, surf_e
436	k = surf_def_v(l)%k(m)
437	tend(k,j,i) = tend(k,j,i) + surf_def_v(l)%mom_flux_uv(m) * ddy
438	ENDDO
439	ENDDO
440	!
441	!-- Natural-type surfaces
442	DO l = 0, 1
443	surf_s = surf_lsm_v(l)%start_index(j,i)
444	surf_e = surf_lsm_v(l)%end_index(j,i)
445	DO m = surf_s, surf_e
446	k = surf_lsm_v(l)%k(m)
447	tend(k,j,i) = tend(k,j,i) + surf_lsm_v(l)%mom_flux_uv(m) * ddy
448	ENDDO
449	ENDDO
450	!
451	!-- Urban-type surfaces
452	DO l = 0, 1
453	surf_s = surf_usm_v(l)%start_index(j,i)
454	surf_e = surf_usm_v(l)%end_index(j,i)
455	DO m = surf_s, surf_e
456	k = surf_usm_v(l)%k(m)
457	tend(k,j,i) = tend(k,j,i) + surf_usm_v(l)%mom_flux_uv(m) * ddy
458	ENDDO
459	ENDDO
460	!
461	!-- Compute vertical diffusion. In case of simulating a surface layer,
462	!-- respective grid diffusive fluxes are masked (flag 8) within this
463	!-- loop, and added further below, else, simple gradient approach is
464	!-- applied. Model top is also mask if top-momentum flux is given.
465	DO k = nzb+1, nzt
466	!
467	!-- Determine flags to mask topography below and above. Flag 1 is
468	!-- used to mask topography in general, and flag 8 implies
469	!-- information about use_surface_fluxes. Flag 9 is used to control
470	!-- momentum flux at model top.
471	mask_bottom = MERGE( 1.0_wp, 0.0_wp, &
472	BTEST( wall_flags_0(k-1,j,i), 8 ) )
473	mask_top = MERGE( 1.0_wp, 0.0_wp, &
474	BTEST( wall_flags_0(k+1,j,i), 8 ) ) * &
475	MERGE( 1.0_wp, 0.0_wp, &
476	BTEST( wall_flags_0(k+1,j,i), 9 ) )
477	flag = MERGE( 1.0_wp, 0.0_wp, &
478	BTEST( wall_flags_0(k,j,i), 1 ) )
479	!
480	!-- Interpolate eddy diffusivities on staggered gridpoints
481	kmzp = 0.25_wp * ( km(k,j,i)+km(k+1,j,i)+km(k,j,i-1)+km(k+1,j,i-1) )
482	kmzm = 0.25_wp * ( km(k,j,i)+km(k-1,j,i)+km(k,j,i-1)+km(k-1,j,i-1) )
483
484	tend(k,j,i) = tend(k,j,i) &
485	+ ( kmzp * ( ( u(k+1,j,i) - u(k,j,i) ) * ddzu(k+1) &
486	+ ( w(k,j,i) - w(k,j,i-1) ) * ddx &
487	) * rho_air_zw(k) * mask_top &
488	- kmzm * ( ( u(k,j,i) - u(k-1,j,i) ) * ddzu(k) &
489	+ ( w(k-1,j,i) - w(k-1,j,i-1) ) * ddx &
490	) * rho_air_zw(k-1) * mask_bottom &
491	) * ddzw(k) * drho_air(k) * flag
492	ENDDO
493
494	!
495	!-- Vertical diffusion at the first surface grid points, if the
496	!-- momentum flux at the bottom is given by the Prandtl law or if it is
497	!-- prescribed by the user.
498	!-- Difference quotient of the momentum flux is not formed over half of
499	!-- the grid spacing (2.0*ddzw(k)) any more, since the comparison with
500	!-- other (LES) models showed that the values of the momentum flux becomes
501	!-- too large in this case.
502	IF ( use_surface_fluxes ) THEN
503	!
504	!-- Default-type surfaces, upward-facing
505	surf_s = surf_def_h(0)%start_index(j,i)
506	surf_e = surf_def_h(0)%end_index(j,i)
507	DO m = surf_s, surf_e
508
509	k = surf_def_h(0)%k(m)
510
511	tend(k,j,i) = tend(k,j,i) &
512	+ ( - ( - surf_def_h(0)%usws(m) ) &
513	) * ddzw(k) * drho_air(k)
514	ENDDO
515	!
516	!-- Default-type surfaces, dowward-facing (except for model-top fluxes)
517	surf_s = surf_def_h(1)%start_index(j,i)
518	surf_e = surf_def_h(1)%end_index(j,i)
519	DO m = surf_s, surf_e
520
521	k = surf_def_h(1)%k(m)
522
523	tend(k,j,i) = tend(k,j,i) &
524	+ ( - surf_def_h(1)%usws(m) &
525	) * ddzw(k) * drho_air(k)
526	ENDDO
527	!
528	!-- Natural-type surfaces, upward-facing
529	surf_s = surf_lsm_h%start_index(j,i)
530	surf_e = surf_lsm_h%end_index(j,i)
531	DO m = surf_s, surf_e
532
533	k = surf_lsm_h%k(m)
534
535	tend(k,j,i) = tend(k,j,i) &
536	+ ( - ( - surf_lsm_h%usws(m) ) &
537	) * ddzw(k) * drho_air(k)
538	ENDDO
539	!
540	!-- Urban-type surfaces, upward-facing
541	surf_s = surf_usm_h%start_index(j,i)
542	surf_e = surf_usm_h%end_index(j,i)
543	DO m = surf_s, surf_e
544
545	k = surf_usm_h%k(m)
546
547	tend(k,j,i) = tend(k,j,i) &
548	+ ( - ( - surf_usm_h%usws(m) ) &
549	) * ddzw(k) * drho_air(k)
550	ENDDO
551
552	ENDIF
553	!
554	!-- Add momentum flux at model top
555	IF ( use_top_fluxes .AND. constant_top_momentumflux ) THEN
556	surf_s = surf_def_h(2)%start_index(j,i)
557	surf_e = surf_def_h(2)%end_index(j,i)
558	DO m = surf_s, surf_e
559
560	k = surf_def_h(2)%k(m)
561
562	tend(k,j,i) = tend(k,j,i) &
563	+ ( - surf_def_h(2)%usws(m) ) * ddzw(k) * drho_air(k)
564	ENDDO
565	ENDIF
566
567
568	END SUBROUTINE diffusion_u_ij
569
570	END MODULE diffusion_u_mod

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