Body:
WRF version: 4.7.1 (WRF-Chem build)
Setup:
Two-domain 2-way nest (feedback=1):
- d01: dx=15 km, grid_fdda=1 (analysis/grid nudging toward an MSM+FNL hybrid analysis; this is working correctly and shows a measurable effect vs. a no-nudging baseline)
- d02: dx=3.75 km, grid_fdda=0
I am trying to add surface-station (AMEDAS, Japan) observation nudging (obs_nudge_opt) on both domains, using an identical OBS_DOMAIN101/OBS_DOMAIN201 pair (per the guide, identical content across domains is fine since WRF ignores obs outside the domain). Current relevant &fdda settings:
obs_nudge_opt = 1, 1,
max_obs = 150000,
fdda_start = 0, 0,
fdda_end = 132120, 132120,
obs_nudge_wind = 1, 1,
obs_coef_wind = 6.0e-2, 6.0e-2, ! intentionally 100x normal, for diagnosis
obs_nudge_temp = 0, 0,
obs_coef_temp = 0.0, 0.0,
obs_nudge_mois = 0, 0,
obs_coef_mois = 0.0, 0.0,
obs_rinxy = 30.0, 30.0,
obs_rinsig = 0.1,
obs_twindo = 0.5, 0.5,
obs_npfi = 10,
obs_ionf = 2, 2,
obs_idynin = 0,
obs_dtramp = 40.0,
obs_ipf_errob = .true.,
obs_ipf_nudob = .true.,
obs_ipf_in4dob = .true.,
and in &time_control:
auxinput11_interval = 1, 1,
(Originally I had auxinput11_interval_s = 60, 60, and obs_rinxy/obs_twindo/obs_ionf given as a single value instead of one per domain — both of which I found documented as pitfalls in Brian Reen's "A Brief Guide to Observation Nudging in WRF" and have since fixed, per below.)
Symptom:
Comparing this run's d02 output against an otherwise-identical run with obs_nudge_opt=0,0 (grid nudging on d01 only, no obs nudging at all) — extracting 10-m wind at ~150 AMEDAS station locations and computing bias/RMSE/MAE against observations — the two cases are bit-for-bit identical (matching to 16 significant digits in the aggregate statistics, and exact at every station/hour when diffing the raw extracted time series). This holds even with obs_coef_wind set to 100x a normal value (6.0e-2 s⁻¹, e-folding time ~17 s) and run for multiple days. If the nudging were having any effect at all, even a small one from imperfect propagation, I would expect at least some tiny nonzero divergence given the chaotic nature of the model — not exact agreement to double precision.
What I've verified so far (all correct):
1. OBS_DOMAIN101/OBS_DOMAIN201 are present and opened correctly ("opening first fdda obs file, fonc=01 inest= 1" / "inest= 2" both appear).
2. rsl.error shows CALL ERROB for both INEST=1 and INEST=2, with NSTA consistently > 0 (~130 for d01, ~120 for d02).
3. The "OBSERVATION NUDGING IS ACTIVATED FOR MESH 2" / "END SETUP DESCRIPTION ... MESH 2" block prints correctly, with TWINDO (hrs) = 0.500 etc., confirming the per-domain namelist values are being read as intended for d02.
4. I traced the full call chain (wrf_fddaobs_in -> in4dob -> ... -> fddaobs_driver -> errob/nudob in module_fddaobs_rtfdda.F) and manually verified, by extracting and positionally diffing the SUBROUTINE nudob(...) dummy-argument list against the actual CALL nudob(...) argument list in module_fddaobs_driver.F (84 arguments), that every argument lines up correctly — in particular iswind<-nudge_wind, giv<-coef_wind, tfaci<-fdob%tfaci are all correctly wired, and tfaci is confirmed to stay at 1.0 (since obs_idynin=0).
5. The n=n+njcsnd loop increment (over NSTAT observations) is present and correct — it is not stuck reprocessing a single station.
6. rindx prints as 2.0 for d01 (30 km / 15 km dx, correct), and the horizontal weighting setup looks consistent for d02 as well.
Question:
Given all of the above checks out, what else could cause the observation-nudging tendency to have zero measurable effect on the model state, even at 100x the normal coefficient over multiple days? Is there a known interaction between grid_fdda on the parent domain + feedback=1 + obs_nudge_opt on the child domain that could suppress this? Or is there another namelist/registry pitfall (in the vein of the auxinput11_interval_s and per-domain-array ones I already found and fixed) that I might be missing?
Happy to share full rsl.error excerpts or the complete namelist on request.
WRF version: 4.7.1 (WRF-Chem build)
Setup:
Two-domain 2-way nest (feedback=1):
- d01: dx=15 km, grid_fdda=1 (analysis/grid nudging toward an MSM+FNL hybrid analysis; this is working correctly and shows a measurable effect vs. a no-nudging baseline)
- d02: dx=3.75 km, grid_fdda=0
I am trying to add surface-station (AMEDAS, Japan) observation nudging (obs_nudge_opt) on both domains, using an identical OBS_DOMAIN101/OBS_DOMAIN201 pair (per the guide, identical content across domains is fine since WRF ignores obs outside the domain). Current relevant &fdda settings:
obs_nudge_opt = 1, 1,
max_obs = 150000,
fdda_start = 0, 0,
fdda_end = 132120, 132120,
obs_nudge_wind = 1, 1,
obs_coef_wind = 6.0e-2, 6.0e-2, ! intentionally 100x normal, for diagnosis
obs_nudge_temp = 0, 0,
obs_coef_temp = 0.0, 0.0,
obs_nudge_mois = 0, 0,
obs_coef_mois = 0.0, 0.0,
obs_rinxy = 30.0, 30.0,
obs_rinsig = 0.1,
obs_twindo = 0.5, 0.5,
obs_npfi = 10,
obs_ionf = 2, 2,
obs_idynin = 0,
obs_dtramp = 40.0,
obs_ipf_errob = .true.,
obs_ipf_nudob = .true.,
obs_ipf_in4dob = .true.,
and in &time_control:
auxinput11_interval = 1, 1,
(Originally I had auxinput11_interval_s = 60, 60, and obs_rinxy/obs_twindo/obs_ionf given as a single value instead of one per domain — both of which I found documented as pitfalls in Brian Reen's "A Brief Guide to Observation Nudging in WRF" and have since fixed, per below.)
Symptom:
Comparing this run's d02 output against an otherwise-identical run with obs_nudge_opt=0,0 (grid nudging on d01 only, no obs nudging at all) — extracting 10-m wind at ~150 AMEDAS station locations and computing bias/RMSE/MAE against observations — the two cases are bit-for-bit identical (matching to 16 significant digits in the aggregate statistics, and exact at every station/hour when diffing the raw extracted time series). This holds even with obs_coef_wind set to 100x a normal value (6.0e-2 s⁻¹, e-folding time ~17 s) and run for multiple days. If the nudging were having any effect at all, even a small one from imperfect propagation, I would expect at least some tiny nonzero divergence given the chaotic nature of the model — not exact agreement to double precision.
What I've verified so far (all correct):
1. OBS_DOMAIN101/OBS_DOMAIN201 are present and opened correctly ("opening first fdda obs file, fonc=01 inest= 1" / "inest= 2" both appear).
2. rsl.error shows CALL ERROB for both INEST=1 and INEST=2, with NSTA consistently > 0 (~130 for d01, ~120 for d02).
3. The "OBSERVATION NUDGING IS ACTIVATED FOR MESH 2" / "END SETUP DESCRIPTION ... MESH 2" block prints correctly, with TWINDO (hrs) = 0.500 etc., confirming the per-domain namelist values are being read as intended for d02.
4. I traced the full call chain (wrf_fddaobs_in -> in4dob -> ... -> fddaobs_driver -> errob/nudob in module_fddaobs_rtfdda.F) and manually verified, by extracting and positionally diffing the SUBROUTINE nudob(...) dummy-argument list against the actual CALL nudob(...) argument list in module_fddaobs_driver.F (84 arguments), that every argument lines up correctly — in particular iswind<-nudge_wind, giv<-coef_wind, tfaci<-fdob%tfaci are all correctly wired, and tfaci is confirmed to stay at 1.0 (since obs_idynin=0).
5. The n=n+njcsnd loop increment (over NSTAT observations) is present and correct — it is not stuck reprocessing a single station.
6. rindx prints as 2.0 for d01 (30 km / 15 km dx, correct), and the horizontal weighting setup looks consistent for d02 as well.
Question:
Given all of the above checks out, what else could cause the observation-nudging tendency to have zero measurable effect on the model state, even at 100x the normal coefficient over multiple days? Is there a known interaction between grid_fdda on the parent domain + feedback=1 + obs_nudge_opt on the child domain that could suppress this? Or is there another namelist/registry pitfall (in the vein of the auxinput11_interval_s and per-domain-array ones I already found and fixed) that I might be missing?
Happy to share full rsl.error excerpts or the complete namelist on request.