refactor nudging code to use cdeps on line remapping and interpolation by mvertens · Pull Request #243 · NorESMhub/CAM

mvertens · 2025-10-30T18:31:06Z

Summary: refactor nudging code to use cdeps on line remapping and interpolation

Contributors: @gold2718

Purpose of changes:
The current nudging code (nudging.F90) requires a single file for every time sample - and often this is every 6 hours. In addition it does not do any mapping from the forcing data to the model grid. Using the CDEPS inline functionality along with its capability to do online horizontal regridding (including for multiple vertical levels) and time interpolation the nudging code has been completely refactored. With this new code - monthly nudging data can be read at just one resolution and the model vertical levels and used with any model grid.
The one change that comes with this is if there is missing data. In the original scheme, if missing data was encountered then the model 'coasted' through the forcing interval and was not nudged. In the new scheme, the time interpolation (linear or upper) is used with the actual data that is available.

To see more details of the inline functionality from CDEPS used here see: https://escomp.github.io/CDEPS/versions/master/html/index.html and in particular https://escomp.github.io/CDEPS/versions/master/html/streams.html#data-model-stream-inline-api

Changes made to build system: None

Changes made to the namelist: The following new namelist variables were introduced:
Nudge_Filenames, Nudge_Meshfile, Nugde_beg_day, Nudge_beg_month, Nudge_beg_year, Nudge_end_day, Nudge_end_month, Nudge_end_year, Nudge_file_times_per_day, Model_update_times_per_day

Changes to the defaults for the boundary datasets: None

Substantial timing or memory changes: TODO - the expectation is that the new code should be faster than the old one since a new file does not have to be opened and closed at every nudging time step. This needs to be confirmed.

Validation:
The following validation was run. using a noresm3_0_beta09 sandbox with this PR and the CDEPS PR NorESMhub/CDEPS#26. Two simulations were done - a reference simulation and a nudging to the reference simulation.

Reference Simulation:

/create_newcase --case /cluster/home/mvertens/noresm/NF1850_ne16pg3_ne16pg3_mtn14_b09_ref --compset 1850_CAM70%LT%NORESM%CAMoslo_CLM60%SP_CICE%PRES_DOCN%DOM_MOSART_DGLC%NOEVOLVE_SWAV_SESP --res ne16pg3_ne16pg3_mtn14 --project nn9560
k --run-unsupported --mach betzy

with the following user_nl_cam

empty_htapes=.true.
nhtfrq = 0, -6, -1,
mfilt  = 1,  28, 168,
ndens  = 2,  2,  2,
fincl2 = 'PS:I','U:I','V:I','T:I','Q:I'
fincl3 = 'PS:I','U:I','V:I','T:I','Q:I','U850:I','V850:I','T850:I','Z500:I'
fincl3lonlat = '11e_60n'

zmconv_c0_lnd             = 0.0075D0
zmconv_c0_ocn             = 0.0075D0
zmconv_ke                 =  5.0E-6
zmconv_ke_lnd             =  1.0E-5
dust_emis_fact            = 6.1D0
clim_modal_aero_top_press = 1.D-4
micro_mg_dcs              = 700.D-6
clubb_c8                  =  5.0D0

Nudging Simulation:

./create_newcase --case /cluster/home/mvertens/noresm/NF1850_ne16pg3_ne16pg3_mtn14_b09_nudging --compset 1850_CAM70%LT%NORESM%CAMoslo_CLM60%SP_CICE%PRES_DOCN%DOM_MOSART_DGLC%NOEVOLVE_SWAV_SESP --res ne16pg3_ne16pg3_mtn14 --project nn
9560k --run-unsupported --mach betzy

The following was set in user_nl_cam:

&nudging_nl
Nudge_Model         = .true.
Nudge_Datapath      = '/cluster/work/users/mvertens/archive/NF1850_ne16pg3_ne16pg3_mtn14_b09_ref/atm/hist'
Nudge_Filenames     = 'NF1850_ne16pg3_ne16pg3_mtn14_b09_ref.cam.h1i.0001-01-01-21600.nc',
                      'NF1850_ne16pg3_ne16pg3_mtn14_b09_ref.cam.h1i.0001-01-08-21600.nc',
                      'NF1850_ne16pg3_ne16pg3_mtn14_b09_ref.cam.h1i.0001-01-15-21600.nc'
Nudge_Meshfile      = '/cluster/shared/noresm/inputdata/share/meshes/ne16pg3_ESMFmesh_cdf5_c20211018.nc'
Nudge_TimeScale_Opt = 0
Nudge_Force_Opt     = 1
Nudge_Uprof         = 1
Nudge_Ucoef         = 1.0
Nudge_Vprof         = 1
Nudge_Vcoef         = 1.0
Nudge_Tprof         = 0
Nudge_Tcoef         = 0.0
Nudge_PSprof        = 0
Nudge_PScoef        = 0.0
Nudge_Qprof         = 0
Nudge_Qcoef         = 0.0
Nudge_beg_year      = 1
Nudge_beg_month     = 1
Nudge_beg_day       = 2
Nudge_end_day       = 14
Nudge_end_month     = 1
Nudge_end_year      = 1
Nudge_taxmode       = 'limit'
Model_update_times_per_day = 48
!
empty_htapes       =.true.
nhtfrq             = 0, -6, -1,
mfilt            = 1,  28, 168,
!mfilt             = 1,   1,   1
ndens              = 2,  2,  2,
fincl2             = 'PS:I','U:I','V:I','T:I','Q:I','Target_U','Target_V','Nudge_U','Nudge_V'
fincl3             = 'PS:I','U:I','V:I','T:I','Q:I','U850:I','V850:I','T850:I','Z500:I',
                     'Target_U','Target_V','Nudge_U','Nudge_V'
fincl3lonlat       = '11e_60n'
!
zmconv_c0_lnd             = 0.0075D0
zmconv_c0_ocn             = 0.0075D0
zmconv_ke                 =  5.0E-6
zmconv_ke_lnd             =  1.0E-5
dust_emis_fact            = 6.1D0
clim_modal_aero_top_press = 1.D-4

Following is the nudging validation:

[ List each test suite run. For each suite, include machine, compiler, and any test failures.
For each failure, include the contents of TestStatus or the output from cs.status.testid for that test ]

Issues addressed by this PR: [ For each issue include a GitHub issue entry, one per line. ]

…r.F90 for model_mesh and model_clock

…sh and model_clock from outside the nuopc cap

…dging

…refactor_nudging2

…o feature/refactor_nudging3

Ovewh · 2026-01-12T10:25:11Z

Plot for the same nudged and reference simulation, but of surface pressure:

gold2718

This work will be a great improvement to NorESM/CAM!

I have a few questions and a bunch of (hopefully easy) change requests.
I have included a set of change requests to refactor how the model is aligned with the nudging data. This is to allow nudging to be turned on and off during a model run while independently choosing which nudging data to use.
Consider moving the cnst_get_ind call in timestep_init to init and make the Q index a module variable. Then, you can remove the call in nudging_timestep_tend (it is not the cheapest function).

gold2718 · 2025-12-12T12:40:37Z

bld/namelist_files/namelist_definition.xml

+<entry id="Nudge_lev_dimname" type="char*256" category="nudging"
+       group="nudging_nl" valid_values="" >
+       Name of vertical dimension in file.
+       Default: none
+       </entry>


Do we need this if we have Nudge_levname (introduced below)? You can easily find the dimension name from the variable name if needed (they should be the same for a coordinate variable).
In addition, it is not used anywhere in the code.
Please remove.

gold2718 · 2025-12-12T13:42:22Z

src/physics/cam/nudging.F90

-  use spmd_utils,     only: mpi_integer, mpi_real8, mpi_logical, mpi_character
-  use cam_logfile,    only: iulog
-  use zonal_mean_mod, only: ZonalMean_t
+  use ESMF


Please dress this naked use statement.

gold2718 · 2025-12-22T09:22:09Z

src/cpl/nuopc/atm_comp_nuopc.F90

   use ESMF                , only : ESMF_DistGrid, ESMF_DistGridCreate
   use ESMF                , only : ESMF_Mesh, ESMF_MeshCreate, ESMF_MeshGet, ESMF_FILEFORMAT_ESMFMESH
   use ESMF                , only : ESMF_Clock, ESMF_ClockGet, ESMF_ClockSet, ESMF_ClockGetNextTime, ESMF_ClockAdvance
+   use ESMF                , only : ESMF_CLockCreate


This is not used anymore, please remove

gold2718 · 2026-02-04T21:05:43Z

src/physics/cam/nudging.F90

+      ! Nudging will never occur, so switch it off
+      Nudge_Model = .false.
+      write(iulog,*) ' '
+      write(iulog,*) 'NUDGING: WARNING - Nudging has been requested by it will'


Typo?

Suggested change

write(iulog,*) 'NUDGING: WARNING - Nudging has been requested by it will'

write(iulog,*) 'NUDGING: WARNING - Nudging has been requested but it will'

gold2718 · 2026-02-05T09:55:10Z

src/physics/cam/nudging.F90

-   allocate(Nudge_PStau(pcols,begchunk:endchunk),stat=istat)
-   call alloc_err(istat,'nudging_init','Nudge_PStau',pcols*((endchunk-begchunk)+1))
+   allocate(Nudge_Utau0(pcols,pver,begchunk:endchunk),stat=istat)
+   call alloc_err(istat,subname,'Nudge_Utau',size3d)


Please correct the error strings here and below?

Suggested change

call alloc_err(istat,subname,'Nudge_Utau',size3d)

call alloc_err(istat,subname,'Nudge_Utau0',size3d)

gold2718 · 2026-02-06T11:43:15Z

bld/namelist_files/namelist_definition.xml

I think that since the Nudge_begin and Nudge_end variables are model times, we need begin and end variables that are specific to the nudging dataset being used (similar to other uses of CDEPS stream info):

<entry id="nudge_data_year_first" type="integer" category="nudging" group="nudging_nl" valid_values="" > First year to use in Nudge_Filenames dataset. Default: none <entry id="nudge_data_year_last" type="integer" category="nudging" group="nudging_nl" valid_values="" > Last year to use in Nudge_Filenames dataset. Default: none </entry>

gold2718 · 2026-02-06T11:48:20Z

src/physics/cam/nudging.F90

+                         Nudge_Force_Opt, Nudge_TimeScale_Opt,                 &
+                         Nudge_Beg_Year, Nudge_Beg_Month, Nudge_Beg_Day,       &
+                         Nudge_End_Year, Nudge_End_Month, Nudge_End_Day,       &
+                         Nudge_Align_Year, Nudge_Mapalgo, Nudge_Taxmode,       &


Based on my comments in namelist_definition.xml, I think this should be:

Suggested change

Nudge_Align_Year, Nudge_Mapalgo, Nudge_Taxmode, &

Nudge_Year_Align, nudge_data_year_first, nudge_data_year_last, Nudge_Mapalgo, Nudge_Taxmode, &

Also, nudge_data_year_first and nudge_data_year_last have to be declared above, and initialized and broadcast below.``

gold2718 · 2026-02-06T11:58:05Z

bld/namelist_files/namelist_definition.xml


+<entry id="Nudge_Align_Year" type="integer" category="nudging"
+       group="nudging_nl" valid_values="" >
+       Model year to align with Nudge_Beg_Year.


Based on comments above, I think this could be clarified:

Suggested change

Model year to align with Nudge_Beg_Year.

Model (simulation) year to align with nudge_data_year_first.

If this is set to Nudge_Beg_Year, then nudging will begin with the beginning of the dataset.

If this is set to some other year, there will be an offset between the model year and the year in the nudging data currently being used.

gold2718 · 2026-02-06T12:00:52Z

src/physics/cam/nudging.F90

+         stream_yearFirst    = nudge_year_first,          &
+         stream_yearLast     = nudge_year_last,           &


Based on comments above, I think this should be:

Suggested change

stream_yearFirst = nudge_year_first, &

stream_yearLast = nudge_year_last, &

stream_yearFirst = nudge_data_year_first, &

stream_yearLast = nudge_data_year_first, &

gold2718 · 2026-02-06T12:01:37Z

src/physics/cam/nudging.F90

+         stream_yearFirst    = nudge_year_first,          &
+         stream_yearLast     = nudge_year_last,           &


Based on comments above, I think this should be:

Suggested change

stream_yearFirst = nudge_year_first, &

stream_yearLast = nudge_year_last, &

stream_yearFirst = nudge_data_year_first, &

stream_yearLast = nudge_data_year_first, &

gold2718

This work will be a great improvement to NorESM/CAM!

I have a few questions and a bunch of (hopefully easy) change requests.
I have included a set of change requests to refactor how the model is aligned with the nudging data. This is to allow nudging to be turned on and off during a model run while independently choosing which nudging data to use.
Consider moving the cnst_get_ind call in timestep_init to init and make the Q index a module variable. Then, you can remove the call in nudging_timestep_tend (it is not the cheapest function).

mvertens and others added 6 commits October 26, 2025 16:41

first pass at refactoring the nudging code

85adf34

fixed compiler issues

17770d2

more refactor of code

e7f5409

migrated atm_stream_nuding.F90 code into nudging.F90 and added atm_sh…

3e6c6bd

…r.F90 for model_mesh and model_clock

fixes to nudging for running

8bb45f1

introduced cam_esmf_mod in src/control to have access to the model_me…

a10e8a5

…sh and model_clock from outside the nuopc cap

mvertens marked this pull request as draft October 30, 2025 18:31

mvertens added the enhancement New feature or request label Oct 31, 2025

mvertens requested a review from gold2718 October 31, 2025 14:27

mvertens assigned gold2718 Oct 31, 2025

mvertens added this to NorESM3.0 model development - tags Oct 31, 2025

github-project-automation bot moved this to Todo in NorESM3.0 model development - tags Oct 31, 2025

mvertens added 2 commits November 1, 2025 20:22

Merge branch 'feature/refactor_nudging_temp' into feature/refactor_nu…

f479a7c

…dging

introduced nudgeing datapath

bb36e8e

mvertens mentioned this pull request Nov 8, 2025

Atmospheric Nudging with NorESM3 spectral element scheme NorESMhub/NorESM#711

Open

gold2718 removed this from NorESM3.0 model development - tags Nov 13, 2025

gold2718 added this to NorESM Development Nov 13, 2025

github-project-automation bot moved this to Todo in NorESM Development Nov 13, 2025

mvertens added 3 commits November 18, 2025 11:37

fixed problem in having nudging be one time step too far ahead

bf6eac3

more refactor of nudging code base

45bb124

more fixes to refactor of nudging

7ab3db0

mvertens mentioned this pull request Dec 1, 2025

noresm3_0_022_cam6_4_121: Use CDEPS for CO2 fossil fuel and aircraft emissions #244

Merged

mvertens added 8 commits December 8, 2025 19:46

mapalgo and tintalgo are now namelist input

afa5c2b

Merge commit 'bf6eac365dac2746dcb8e5e61d99af0645a6c9a2' into feature/…

e2289df

…refactor_nudging2

Merge commit '7ab3db06d8153e635e0b2ee5977e17295525d8a8' into feature/…

06f1855

…refactor_nudging2

Merge commit 'afa5c2bc4cc2989e8a0c6a9de8d346e257042361' into feature/…

68cff4a

…refactor_nudging2

new default settings for namelists - particularly nudging_align_year

a50100a

fixed namelist checking to work only if nudge_model is on

93e6f46

fixed standard out issues from nudging

9493bdb

fixed log output

d0ae463

mvertens added 2 commits December 19, 2025 19:16

fixed standard output

5c81892

Merge remote-tracking branch 'mvertens/feature/refactor_nudging2' int…

875a455

…o feature/refactor_nudging3

mvertens force-pushed the feature/refactor_nudging branch from 40ad302 to 875a455 Compare December 20, 2025 22:21

merged to head of noresm_develop

e1e44e8

mvertens marked this pull request as ready for review December 30, 2025 16:52

fixed bug in stream_yearAlign for PS

f2d10a2

gold2718 requested changes Feb 6, 2026

View reviewed changes

github-project-automation bot moved this from Todo to In Progress in NorESM Development Feb 6, 2026

gold2718 requested changes Feb 6, 2026

View reviewed changes

	write(iulog,*) 'NUDGING: WARNING - Nudging has been requested by it will'
	write(iulog,*) 'NUDGING: WARNING - Nudging has been requested but it will'

	call alloc_err(istat,subname,'Nudge_Utau',size3d)
	call alloc_err(istat,subname,'Nudge_Utau0',size3d)

	Nudge_Align_Year, Nudge_Mapalgo, Nudge_Taxmode, &
	Nudge_Year_Align, nudge_data_year_first, nudge_data_year_last, Nudge_Mapalgo, Nudge_Taxmode, &

-       Model year to align with Nudge_Beg_Year.
+       Model (simulation) year to align with nudge_data_year_first.
+       If this is set to Nudge_Beg_Year, then nudging will begin with the beginning of the dataset.
+       If this is set to some other year, there will be an offset between the model year and the year in the nudging data currently being used.

		stream_yearFirst = nudge_year_first, &
		stream_yearLast = nudge_year_last, &

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mvertens commented Oct 30, 2025 •

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