Add Spectral Nudging Option and Fix Nudging Behavior When Files Are Missing

[patcal]

This pull request addresses issues #1393 and #1273

For Issue #1273 an error exit with a message is invoked if a missing nudging file is encountered.

For Issue #1393 a module for computing spherical harmonics on the physics grid is implemented. The nudging module has additional functionality that uses this module to optionally filter nudging tendencies to scales larger then a specified truncation scale.

This functionality is controlled by 2 additional variables in the &nudging_nl namelist.
Nudge_SpectralFilter- LOGICAL Option to apply spherical harminic filtering to
the model state and target data so that nudging
tendencies are only applied to scales larger than
the specified truncation.

Nudge_SpectralNtrunc - INT The number of meridional spherical harmonic modes used
for spectral filtering. The nominal horizontal scale of
the filtering can be estimated as:

                                                          Hscale = PI*6350/Nudge_SpectralNtrunc

                                          i.e. Nudge_SpectralNtrunc=40 corresponds to a horizontal 
                                                 nudging scale  Hscale~500km.

[fvitt]

Some initial questions and comments. Do you have a test case for spectral nudging that you can point me to? I can implement a regression test case.

[fvitt]

I am not seeing where Nudge_SpectralNbasis gets sets. Is it always -1?

[patcal]

Hi @fvitt , for the spherical harmonics, the user specifies the meridional truncation(L). For each index (l < L+1) there are (2l+1) basis functions, so the init() routine sums up the total number of these basis functions and returns the value into Nudge_SpectralNbasis.

[jtruesdal]

@patcal @fvitt was there ever a regression test added so we can verify if something gets broken in a future commit.

[fvitt]

We have these aux_cam tests:

aux_cam           : ERP_Ln9.ne30pg3_ne30pg3_mg17.FCnudged.derecho_intel.cam-outfrq9s
aux_cam           : SMS_D_Ln9.f09_f09_mg17.FCts2nudged.derecho_intel.cam-outfrq9s_leapday

and these prealpha and prebeta tests:

prealpha          : ERP_Ln9.f09_f09_mg17.FCnudged_GC.derecho_intel.cam-outfrq9s
prealpha          : SMS_D_Ln9_P1536x1.ne0CONUSne30x8_ne0CONUSne30x8_mt12.FCnudged.derecho_intel.cam-outfrq9s                                                   # "Nudged CAM-Chem on a regionally refined grid"
prebeta           : SMS_D_Ln9.f09_f09_mg17.FCnudged.derecho_intel.cam-outfrq3s_zmean_nudging                                                                   # Zonal Mean Nudged

[jtruesdal]

Thanks @patcal I'll see if I can update this to the head of the trunk.

[jtruesdal]

This is a nice refactor. I didn't test the code to pull shr_reprosum out of the level loop it was just an example but something like that should work.

[patcal]

Hi John, Sorry for the confusion. The last test I ran last night before pushing the mods had a 50% increase in runtime, so something I did is causing problems that I am trying to undo. I thought I might be able to get it sorted out before this morning. I will go ahead and update with the current files shortly so you and Francis can go through the revisions. The problem seems to be isolated to one use case, so I will need to add a patch for nudging.F90 to fix cases with user-defined nudging windows (Nudge_Xprof=3 cases) as soon as I get it worked out.

…

--> Patrick

On Tue, Jun 23, 2026 at 9:03 AM jtruesdal ***@***.***> wrote: ***@***.**** commented on this pull request. ------------------------------ In src/utils/ug_spectralmethods_mod.F90 <#1402 (comment)>: > + + Csum(:,:) = 0._r8 + Gcov(:) = 0._r8 + + do nn= 1,this%nbas + count = 0 + do lchnk=begchunk,endchunk + ncols = get_ncols_p(lchnk) + do cc = 1,ncols + count=count+1 + Csum(count,nn) = I_Gdata(cc,ll,lchnk)*this%basis(cc,lchnk,nn)*this%area(cc,lchnk) + end do + end do + end do + + call shr_reprosum_calc(Csum, Gcov, count, nlcols, this%nbas, gbl_count=ngcols_p, commid=mpicom) Same as above. I don't see the mods. — Reply to this email directly, view it on GitHub <#1402?email_source=notifications&email_token=AJMQHAOZGO77LLLC63HKZXT5BKL3ZA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGQ2TAOBQGIZKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#discussion_r3460760759>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AJMQHAICCQL6TZ4V55A7AMT5BKL3ZAVCNFSNUABFKJSXA33TNF2G64TZHMZDANBYGQ2DGNBRHNEXG43VMU5TGNBWG43DGMBWGE42C5QC> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/AJMQHALGHQZWKTC2ORSIL2T5BKL3ZA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGQ2TAOBQGIZKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJKTGN5XXIZLSL5UW64Y> and Android <https://github.com/notifications/mobile/android/AJMQHALAPZLOTCUYOCURL6T5BKL3ZA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGQ2TAOBQGIZKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. Download it today! You are receiving this because you were mentioned.Message ID: ***@***.***>

[jtruesdal]

Thanks Pat. jt

…

On Tue, Jun 23, 2026 at 10:44 AM patcal ***@***.***> wrote: *patcal* left a comment (ESCOMP/CAM#1402) <#1402 (comment)> Hi John, Sorry for the confusion. The last test I ran last night before pushing the mods had a 50% increase in runtime, so something I did is causing problems that I am trying to undo. I thought I might be able to get it sorted out before this morning. I will go ahead and update with the current files shortly so you and Francis can go through the revisions. The problem seems to be isolated to one use case, so I will need to add a patch for nudging.F90 to fix cases with user-defined nudging windows (Nudge_Xprof=3 cases) as soon as I get it worked out. --> Patrick On Tue, Jun 23, 2026 at 9:03 AM jtruesdal ***@***.***> wrote: > ***@***.**** commented on this pull request. > ------------------------------ > > In src/utils/ug_spectralmethods_mod.F90 > <#1402 (comment)>: > > > + > + Csum(:,:) = 0._r8 > + Gcov(:) = 0._r8 > + > + do nn= 1,this%nbas > + count = 0 > + do lchnk=begchunk,endchunk > + ncols = get_ncols_p(lchnk) > + do cc = 1,ncols > + count=count+1 > + Csum(count,nn) = I_Gdata(cc,ll,lchnk)*this%basis(cc,lchnk,nn)*this%area(cc,lchnk) > + end do > + end do > + end do > + > + call shr_reprosum_calc(Csum, Gcov, count, nlcols, this%nbas, gbl_count=ngcols_p, commid=mpicom) > > Same as above. I don't see the mods. > > — > Reply to this email directly, view it on GitHub > < #1402?email_source=notifications&email_token=AJMQHAOZGO77LLLC63HKZXT5BKL3ZA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGQ2TAOBQGIZKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#discussion_r3460760759>, > or unsubscribe > < https://github.com/notifications/unsubscribe-auth/AJMQHAICCQL6TZ4V55A7AMT5BKL3ZAVCNFSNUABFKJSXA33TNF2G64TZHMZDANBYGQ2DGNBRHNEXG43VMU5TGNBWG43DGMBWGE42C5QC> > . > Triage notifications, keep track of coding agent tasks and review pull > requests on the go with GitHub Mobile for iOS > < https://github.com/notifications/mobile/ios/AJMQHALGHQZWKTC2ORSIL2T5BKL3ZA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGQ2TAOBQGIZKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJKTGN5XXIZLSL5UW64Y> > and Android > < https://github.com/notifications/mobile/android/AJMQHALAPZLOTCUYOCURL6T5BKL3ZA5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGQ2TAOBQGIZKM4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. > Download it today! > You are receiving this because you were mentioned.Message ID: > ***@***.***> > — Reply to this email directly, view it on GitHub <#1402?email_source=notifications&email_token=ACG3NX3OC7U7VAJ2D4N6MRD5BKXWVA5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTINZYGE2DEOBUGE2KM4TFMFZW63VGMFZXG2LHN2SWK5TFNZ2KYZTPN52GK4S7MNWGSY3L#issuecomment-4781428414>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ACG3NX2J247C3R5EJ7EN4N35BKXWVAVCNFSNUABFKJSXA33TNF2G64TZHMZDANBYGQ2DGNBRHNEXG43VMU5TGNBWG43DGMBWGE42C5QC> . You are receiving this because you were assigned.Message ID: ***@***.***>

[jtruesdal]

All looks good now for me.

[patcal]

Thanks John, I will try and get the Nudge_Xprof=3 problem resolved today.

…

--> Patrick

On Tue, Jun 23, 2026 at 1:27 PM jtruesdal ***@***.***> wrote: ***@***.**** approved this pull request. All looks good now for me. — Reply to this email directly, view it on GitHub <#1402?email_source=notifications&email_token=AJMQHANDKVAVL5XRKMZLJZL5BLK23A5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGY2DKNBXG422M4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#pullrequestreview-4556454775>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AJMQHAIXITRKVMTG6DZ64DT5BLK23AVCNFSNUABFKJSXA33TNF2G64TZHMZDANBYGQ2DGNBRHNEXG43VMU5TGNBWG43DGMBWGE42C5QC> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/AJMQHAMUUEBNJHBWZAMZYKT5BLK23A5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGY2DKNBXG422M4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJKTGN5XXIZLSL5UW64Y> and Android <https://github.com/notifications/mobile/android/AJMQHAJRD7Z5EJMLHZ4GBZT5BLK23A5CNFSNUABKM5UWIORPF5TWS5BNNB2WEL2QOVWGYUTFOF2WK43UKJSXM2LFO4XTINJVGY2DKNBXG422M4TFMFZW63VHNVSW45DJN5XKKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. Download it today! You are receiving this because you were mentioned.Message ID: ***@***.***>

[fvitt]

Looks good to me, assuming the nudged regression tests pass if they are expected to.