Revised PR#995 for adding analysis grid nudging capability by maywswong · Pull Request #1481 · MPAS-Dev/MPAS-Model

maywswong · 2026-07-02T16:20:24Z

This PR is created to merge code changes related to adding an analysis grid nudging capability in MPAS-A. The core of the code changes was presented in Bullock et al. (2018) and PR #995. In this PR, several updates and revisions are made to PR #995 and are as follow.

(1) Added capabilities in init_atmosphere_model to generate the target "FDDA" analysis files that are required for input to atmosphere_model when the analysis nudging option is turned on, instead of using an offline script as presented in PR #995. See below for instructions on generating target files using init_atmosphere.

(2) Calls to the computation of the nudging tendencies are implemented similar to those for other additional tendency terms, such as those from Incremental Analysis Update (IAU), instead of adding the nudging tendencies inside the physics as implemented in PR #995.

(3) Renamed new variables in PR #995 (XX_fdda_new, XX_fdda_old) to a more concise two-time-level variables (XX_fdda). Also renamed the namelist record in namelist.atmosphere from &fdda to &nudging.

========= Instructions for generating and using files with nudging target fields =========

To generate the nudging target files using init_atmosphere (e.g., from six-hourly analyses):

a. Create your init.nc file as usual. This step needs to be done prior to generating the nudging files because init.nc contains the vertical and horizontal mesh information needed for interpolating the analyses onto the MPAS mesh.

b. In namelist.init_atmosphere, set config_init_case = 11, and set config_start_time and config_stop_time to reflect the beginning and end of your simulation period. The corresponding preprocessed six-hourly intermediate files should reside in the run directory, or as defined by config_met_prefix (similar to when generating lateral boundary condition files for a regional simulation).

c. In streams.init_atmosphere, add the immutable output stream for the target files:

<immutable_stream name="fdda"
                  type="output"
                  filename_template="fdda.$Y-$M-$D_$h.$m.$s.nc"
                  filename_interval="output_interval"
                  packages="fdda"
                  clobber_mode="replace_files"
                  output_interval="06:00:00" />

d. When running MPAS-atmosphere, use the same filename_template when defining the immutable input stream in streams.atmosphere:

<immutable_stream name="fdda"
                  type="input"
                  filename_template="fdda.$Y-$M-$D_$h.$m.$s.nc"
                  input_interval="6:00:00" />

e. When running MPAS-atmosphere, add the following example namelist record to use nudging option:

&nudging
    config_fdda_scheme = 'analysis'
    config_fdda_t = true
    config_fdda_q = false
    config_fdda_uv = true
    config_fdda_uv_in_pbl = false
    config_fdda_t_in_pbl = false
    config_fdda_q_in_pbl = false
/

Namelist option config_fdda_scheme set to 'analysis' ('off') turns on (off) the nudging option.

=====================================================================

Reference:
Bullock Jr., O. R., H. Foroutan, R. C. Gilliam, and J. A. Herwehe, 2018:
Adding four-dimensional data assimilation by analysis nudging to the
Model for Prediction Across Scales – Atmosphere (version 4.0). Geosci.
Model Dev., 11, 2897–2922. https://doi.org/10.5194/gmd-11-2897-2018

Related PR: #995

This EPA_FDDA commit will add 3-D grid analysis nudging FDDA to MPAS-A as an option to assist in keeping retrospective simulations dynamically on track to improve evaluation against observations. This FDDA development for MPAS-A (Bullock et al., 2018) nudges temperature, humidity, and wind toward target values and is based on the comparable FDDA feature available in WRF, including MPAS-A versions of many of the WRF FDDA options. Enabling analysis nudging FDDA in MPAS-A maintains high fidelity to the reference fields while still conserving mass. An extra step (additional details are provided in the associated pull request) using init_atmosphere_model is necessary to generate the FDDA file required for input to a subsequent MPAS-A simulation with FDDA enabled. New file: src/core_atmosphere/physics/mpas_atmphys_fdda.F Modified files: Makefile src/core_atmosphere/Registry.xml src/core_atmosphere/physics/Makefile src/core_atmosphere/physics/mpas_atmphys_control.F src/core_atmosphere/physics/mpas_atmphys_driver.F src/core_atmosphere/physics/mpas_atmphys_manager.F src/core_atmosphere/physics/mpas_atmphys_todynamics.F src/core_init_atmosphere/Registry.xml These EPA_FDDA code changes to MPAS-A are based on the 22 August 2022 "develop" branch of MPAS v7.3. Reference: Bullock Jr., O. R., H. Foroutan, R. C. Gilliam, and J. A. Herwehe, 2018: Adding four-dimensional data assimilation by analysis nudging to the Model for Prediction Across Scales Atmosphere (version 4.0). Geosci. Model Dev., 11, 28972922. https://doi.org/10.5194/gmd-11-2897-2018

…iles using provided intermediate files. Tested for GFS intermediate files and FDDA input files generated at the same file interval as fg_interval.

…lar to mpas_atm_iau.F The FDDA scheme originally in physics/mpas_atmphys_fdda.F is now dynamics/mpas_atm_fdda.F, with added variable transformation and passing of FDDA tendencies to the dynamics through "tend_ru_physics, tend_rtheta_physics". Other changes include moving the FDDA configuration options in the namelist out of the physics namelist record and into its own fdda namelist record.

…cs variable structure to its own tend_fdda variable structure in the Registry.

…cs variable structure to its own tend_fdda variable structure in the Registry. *Modified the call to apply_fdda to include tend_fdda

… two time levels. FDDA input fields are read in and shifted in time levels, similar to how LBC fields are done.

1. Remove changes to Makefile from original PR 2. Add new fdda variables and remove the old in registry 3. Add missed argument xtime_s to calls to atm_srk3 and atm_timestep

…1 release

…structZ_fdda from the fdda_state variable structure in core_init_atmosphere, so they are not output by default in the FDDA target files. * Setting config_init_case = 11 in core_init_atmosphere to be the analysis nudging case

…tm_fdda.F

…ure. To minimize the output fields needed in the target analysis nudging files written out, modified the default output variables for the fdda stream instead.

…gurations from 'fdda' to 'nudging' in atmosphere_model.

…grid-nudging

mgduda · 2026-09-23T20:41:52Z

   end function atm_get_sounding_2

 !-----------
+<<<<<<< HEAD


I think you'll need to remove the git conflict markers here and lines 7803-7804.

mgduda · 2026-09-23T20:43:05Z

+ public:: physics_get_tend, pre_physics_get_tend, post_physics_get_tend, tend_toEdges
+=======
 public:: physics_get_tend, pre_physics_get_tend, post_physics_get_tend
+>>>>>>> 91c5eac175eebeaf4206bacd5cb50c39dff3c152


This looks like an unresolved git merge conflict.

mgduda · 2026-09-23T21:16:52Z

+                <var name="v_fdda" type="real" dimensions="nVertLevels nCells Time" units="m s^{-1}"
+                     description="meridional wind component for FDDA grid nudging"/>
+
+        </var_struct>


So that these fields aren't allocated for simulations that don't make use of FDDA, we could define a new package and attach it to these fields.

mgduda · 2026-09-23T21:21:36Z

    config_radt_lw_scheme    .ne. 'off' .or. &
    config_radt_sw_scheme    .ne. 'off' .or. &
-    config_sfclayer_scheme   .ne. 'off') then
+    config_sfclayer_scheme   .ne. 'off') then 


It doesn't look like any of the changes in mpas_atmphys_driver.F are related to FDDA, so perhaps we could revert them.

mgduda · 2026-09-23T22:53:52Z


+		<stream name="fdda" 
+                        type="input" 
+                        filename_template="x1.40962.fdda.nc" 


Just a small usability suggestion: we could set the default filename_template here to match the default filename_template used for the "fdda" stream in the init_atmosphere core (i.e., fdda.$Y-$M-$D_$h.$m.$s.nc).

maywswong · 2026-09-25T20:34:31Z

Hi Jerry @jherwehe -- @mgduda and I wanted to reach out to you but had trouble reaching you via perhaps an old email address. We wanted to know, since this PR here is heavily based on your previous work PR #995, would you have any additional input/comments/concerns on these modifications (which pertain mostly to how the target files are generated and also where the nudging code resides within MPAS)? If there's an easier way to reach out to you so we can touch base, that would be helpful! Thanks so much!

jherwehe and others added 18 commits August 17, 2025 02:03

Adding new init_case = 10 in init_atmosphere to generate FDDA input f…

27022fd

…iles using provided intermediate files. Tested for GFS intermediate files and FDDA input files generated at the same file interval as fg_interval.

Changing FDDA stream variables from *_fdda_new to *_fdda.

dd27c4a

Changing th_fdda to theta_fdda

7d37aa4

Moving FDDA tendency variables (rthfddaten, etc.) from the tend_physi…

8047f3c

…cs variable structure to its own tend_fdda variable structure in the Registry.

Moving FDDA tendency variables (rthfddaten, etc.) from the tend_physi…

4ba4a78

…cs variable structure to its own tend_fdda variable structure in the Registry. *Modified the call to apply_fdda to include tend_fdda

Moving *_fdda_new, *_fdda_old variables into one variable *_fdda with…

9a6b6bf

… two time levels. FDDA input fields are read in and shifted in time levels, similar to how LBC fields are done.

Corrections from rebasing:

3ae1014

1. Remove changes to Makefile from original PR 2. Add new fdda variables and remove the old in registry 3. Add missed argument xtime_s to calls to atm_srk3 and atm_timestep

Merging modifications based on the EPA analysis nudging tool to V8.4.…

601cf8f

…1 release

Removing mpas_log_write statements in core_atmosphere/dynamics/mpas_a…

6feeb70

…tm_fdda.F

Added uReconstructX_fdda, etc. back to the fdda_state variable struct…

1bca336

…ure. To minimize the output fields needed in the target analysis nudging files written out, modified the default output variables for the fdda stream instead.

Output scalars_fdda, not qv_fdda.

3348fcc

In Registry.xml, scalars_fdda is a var_array, not variable.

2aec7d9

Corrected typo in Registry.xml

a16f533

Change the name of the namelist record for the nudging namelist confi…

cf6211b

…gurations from 'fdda' to 'nudging' in atmosphere_model.

Merge branch 'master' of https://github.com/MPAS-Dev/MPAS-Model into …

6c57483

…grid-nudging

mgduda changed the base branch from master to develop September 23, 2026 20:27

mgduda self-requested a review September 23, 2026 20:40

mgduda added feature Atmosphere labels Sep 23, 2026

mgduda reviewed Sep 23, 2026

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Revised PR#995 for adding analysis grid nudging capability - #1481

Revised PR#995 for adding analysis grid nudging capability#1481
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