Switch CESM to netCDF restarts with binary fallback; in-core calm IC

Make netCDF (PIO) restarts the default for CESM while keeping binary
restarts as a coexisting, backward-compatible fallback, and start
initial runs from in-core calm conditions rather than a binary
calm_strt.ww3 file.

- wav_comp_nuopc.F90: set use_restartnc=.true. for CESM; defer model
  init (waveinit_cesm/wav_history_init) to InitializeRealize after
  wav_pio_init, since CESM PIO is only set up at PostChildrenAdvertise.
- w3initmd.F90: CESM restart read selects netCDF vs binary by the
  initfile extension (.nc -> read_restart, else -> binary w3iors
  fallback); an initial run with no initfile starts from in-core calm
  (read_restart('none')).
- w3iorsmd.F90: accept a legacy-version binary restart ('2021-05-28')
  with a warning instead of aborting -- the FULL-restart record layout
  is unchanged, so hybrid/branch runs stay backward compatible with
  pre-merge binary restarts.
- w3wavemd.F90: keep the CESM gridded-output/coupling-export handling
  (which keeps the HS/Stokes/period arrays current for the mediator
  export) and write netCDF restarts via wav_restart_mod when
  use_restartnc.
- wav_history_mod.F90: skip the per-history indicator log file for CESM
  (#ifndef W3_CESMCOUPLED); retained for UFS.

Validated against the 30a09a baseline: aux_ww3 (ERS/ERI/SMS_D/SMS-CW/
SMS-legacy_cpl) -- cpl.hi/cpl.hx.ww3/mom6 identical, exact-restart and
branch/hybrid comparisons pass, only the known ww3.hi THM convention
delta remains; plus multi-instance netCDF exact-restart (ERS _C3) and
branch/hybrid from pre-merge binary restarts all pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: alperaltuntas

model/src/w3initmd.F90

@@ -454,6 +454,7 @@ SUBROUTINE W3INIT ( IMOD, IsMulti, FEXT, MDS, MTRACE, ODAT, FLGRD,  FLGR2, FLGD,
 #ifdef W3_PIO
     use wav_restart_mod, only : read_restart
     use w3odatmd,        only : runtype, restart_from_binary, use_restartnc, user_restfname
+    use w3odatmd,        only : use_user_restname, initfile
 #endif
     !/
 #ifdef W3_MPI
@@ -983,6 +984,40 @@ SUBROUTINE W3INIT ( IMOD, IsMulti, FEXT, MDS, MTRACE, ODAT, FLGRD,  FLGR2, FLGD,
 #ifdef W3_PIO
     if (use_restartnc) then
       call set_user_timestring(time,user_timestring)
+#ifdef W3_CESMCOUPLED
+      ! CESM: netCDF restarts are the default; binary restart/IC files are a
+      ! coexisting, backward-compatible fallback selected by the initfile
+      ! extension. An initial run with no initfile starts from in-core calm
+      ! conditions (read_restart('none')) -- no binary initial-condition file.
+      if (trim(runtype) == 'continue') then
+        fname = trim(user_restfname)//trim(user_timestring)//'.nc'
+        inquire(file=trim(fname), exist=exists)
+        if (.not. exists) then
+          call extcde (60, msg="required restart file " // trim(fname) // " does not exist")
+        end if
+        call read_restart(trim(fname), va=va, mapsta=mapsta, mapst2=mapst2)
+      else if (len_trim(initfile) == 0) then
+        if (trim(runtype) == 'branch') then
+          call extcde (60, msg="branch run requires a non-empty initfile")
+        end if
+        ! initial run with no IC file: start from in-core calm conditions
+        call read_restart('none')
+        flcold = .true.
+      else
+        inquire(file=trim(initfile), exist=exists)
+        if (.not. exists) then
+          call extcde (60, msg="required IC/restart file " // trim(initfile) // " does not exist")
+        end if
+        if (index(initfile, '.nc', back=.true.) == len_trim(initfile) - 2) then
+          ! netCDF IC/restart file
+          call read_restart(trim(initfile), va=va, mapsta=mapsta, mapst2=mapst2)
+        else
+          ! binary IC/restart file (backward-compatible fallback)
+          call w3iors('READ', nds(6), sig(nk), imod, filename=trim(initfile))
+          flcold = rstype <= 1 .or. rstype == 4
+        end if
+      end if
+#else
       if (restart_from_binary) then
         fname = trim(user_restfname)//trim(user_timestring)
       else
@@ -998,14 +1033,14 @@ SUBROUTINE W3INIT ( IMOD, IsMulti, FEXT, MDS, MTRACE, ODAT, FLGRD,  FLGR2, FLGD,
       else
         if (runtype == 'continue') then
           call extcde (60, msg="required restart file " // trim(fname) // " does not exist")
-        elseif (restart_from_binary) then 
+        elseif (restart_from_binary) then
           call extcde (60, msg="required restart file " // trim(fname) // " does not exist")
-        else 
+        else
           call read_restart('none')
-         ! mapst2 is module variable defined in read of mod_def; maptst is from 2.b above
-         flcold = .true.
-        endif 
+          flcold = .true.
+        endif
       end if
+#endif
     else
 #endif
 

model/src/w3iorsmd.F90

@@ -617,9 +617,20 @@ SUBROUTINE W3IORS ( INXOUT, NDSR, DUMFPI, IMOD, FLRSTRT , filename)
           CALL EXTCDE ( 10 )
         END IF
         IF ( VERTST .NE. VERINI ) THEN
-          IF ( IAPROC .EQ. NAPERR )                               &
-               WRITE (NDSE,902) VERTST, VERINI
-          CALL EXTCDE ( 11 )
+          ! Backward compatibility: the FULL-type restart record layout is
+          ! unchanged between version '2021-05-28' (CESM3 release / dev_unified)
+          ! and the current VERINI -- the only differences in W3IORS are the
+          ! version-string bump and a GOTO cleanup. A legacy-version restart can
+          ! therefore be read safely; accept it with a warning instead of
+          ! aborting, so hybrid/branch runs remain backward compatible.
+          IF ( VERTST .EQ. '2021-05-28' ) THEN
+            IF ( IAPROC .EQ. NAPERR )                             &
+                 WRITE (NDSE,9021) VERTST, VERINI
+          ELSE
+            IF ( IAPROC .EQ. NAPERR )                             &
+                 WRITE (NDSE,902) VERTST, VERINI
+            CALL EXTCDE ( 11 )
+          END IF
         END IF
         IF ( TNAME .NE. GNAME ) THEN
           IF ( IAPROC .EQ. NAPERR )                               &
@@ -1640,6 +1651,10 @@ SUBROUTINE W3IORS ( INXOUT, NDSR, DUMFPI, IMOD, FLRSTRT , filename)
 902 FORMAT (/' *** WAVEWATCH III ERROR IN W3IORS :'/                &
          '     ILLEGAL VERINI, READ : ',A/                      &
          '                    CHECK : ',A/)
+9021 FORMAT (/' *** WAVEWATCH III WARNING IN W3IORS :'/             &
+         '     READING LEGACY-VERSION RESTART, READ : ',A/       &
+         '                                  CURRENT : ',A/       &
+         '     RECORD LAYOUT IS COMPATIBLE; CONTINUING.'/)
 903 FORMAT (/' *** WAVEWATCH III WARNING IN W3IORS :'/              &
          '     ILLEGAL GNAME, READ : ',A/                       &
          '                   CHECK : ',A/)

model/src/w3wavemd.F90

@@ -560,7 +560,9 @@ SUBROUTINE W3WAVE ( IMOD, ODAT, TEND, STAMP, NO_OUT &
     use w3odatmd      , only : histwr, rstwr
 #ifdef W3_PIO
     use wav_history_mod , only : write_history
-    USE W3ODATMD,         ONLY : FNMRST
+    use wav_restart_mod , only : write_restart
+    use w3timemd        , only : set_user_timestring
+    USE W3ODATMD,         ONLY : FNMRST, user_restfname
     USE W3GDATMD,         ONLY : MAPST2
 #endif
     use w3odatmd        , only : use_historync, use_restartnc
@@ -693,6 +695,10 @@ SUBROUTINE W3WAVE ( IMOD, ODAT, TEND, STAMP, NO_OUT &
     logical, parameter :: w3_cesmcoupled_flag = .false.
 #endif
     integer :: memunit
+#ifdef W3_PIO
+    character(len=512) :: rstfname           ! netCDF restart filename
+    character(len=16)  :: rst_timestring     ! YYYY-MM-DD-SSSSS
+#endif
     logical :: do_gridded_output
     logical :: do_point_output
     logical :: do_track_output
@@ -2744,8 +2750,17 @@ SUBROUTINE W3WAVE ( IMOD, ODAT, TEND, STAMP, NO_OUT &
                 CALL W3IOTR ( NDS(11), NDS(12), VA, IMOD )
 
               ELSE IF ( do_restart_output ) THEN
-                CALL W3IORS ('HOT', NDS(6), XXX, IMOD, FLOUT(8) )
-                ITEST = RSTYPE
+                if (use_restartnc) then
+#ifdef W3_PIO
+                  ! netCDF (PIO) restart: casename.ww3.r.YYYY-MM-DD-SSSSS.nc
+                  call set_user_timestring(time, rst_timestring)
+                  rstfname = trim(FNMRST)//trim(user_restfname)//trim(rst_timestring)//'.nc'
+                  call write_restart(trim(rstfname), va, mapsta+8*mapst2)
+#endif
+                else
+                  CALL W3IORS ('HOT', NDS(6), XXX, IMOD, FLOUT(8) )
+                  ITEST = RSTYPE
+                end if
 
               ELSE IF ( do_wavefield_separation_output ) THEN
                 IF ( IAPROC .EQ. NAPBPT ) THEN

model/src/wav_comp_nuopc.F90

@@ -620,9 +620,12 @@ subroutine InitializeAdvertise(gcomp, importState, exportState, clock, rc)
         user_histfname = trim(casename)//'.ww3.hi.'
       endif
 
-      ! netcdf (PIO) is used for CESM gridded history output; restarts
-      ! remain binary, with the initial file read via initfile (see waveinit_cesm)
+      ! netcdf (PIO) is used for CESM gridded history output and restarts.
+      ! Initial and branch runs still read the binary initial-condition file
+      ! provided via initfile (see waveinit_cesm); continue runs read the
+      ! netcdf restart written by wav_restart_mod.
       use_historync = .true.
+      use_restartnc = .true.
     else
       call NUOPC_CompAttributeGet(gcomp, name='use_restartnc', value=cvalue, isPresent=isPresent, isSet=isSet, rc=rc)
       if (ChkErr(rc,__LINE__,u_FILE_u)) return
@@ -680,16 +683,15 @@ subroutine InitializeAdvertise(gcomp, importState, exportState, clock, rc)
     ! Wave model initialization
     !--------------------------------------------------------------------
 
-    time = time0
+    ! In CESM, wave model initialization (w3init) is deferred to
+    ! InitializeRealize: w3init reads the netCDF restart, which requires PIO,
+    ! and CESM PIO is only set up by the driver after the advertise phase
+    ! (PostChildrenAdvertise). For UFS, model init stays here in the advertise
+    ! phase, matching emc.
 #ifndef W3_CESMCOUPLED
+    time = time0
     call waveinit_ufs(gcomp, stdout, ntrace, mpicomm, mds, rc)
     if (ChkErr(rc,__LINE__,u_FILE_u)) return
-#else
-    call ESMF_ClockGet( clock, timeStep=timeStep, rc=rc)
-    if (ChkErr(rc,__LINE__,u_FILE_u)) return
-    call waveinit_cesm(gcomp, ntrace, mpicomm, mds, rc)
-    if (ChkErr(rc,__LINE__,u_FILE_u)) return
-#endif
     !call mpi_barrier ( mpicomm, ierr )
     if ( root_task ) then
       inquire(unit=stdout, name=logfile)
@@ -712,6 +714,7 @@ subroutine InitializeAdvertise(gcomp, importState, exportState, clock, rc)
     if (use_historync) then
       call wav_history_init(stdout)
     end if
+#endif
 
     call advertise_fields(importState, exportState, flds_scalar_name, rc)
     if (ChkErr(rc,__LINE__,u_FILE_u)) return
@@ -751,11 +754,15 @@ subroutine InitializeRealize(gcomp, importState, exportState, clock, rc)
 
     use w3odatmd    , only : naproc
     use w3gdatmd    , only : mapsf
-    use w3gdatmd    , only : nx, ny, ungtype, gtype, nseal, nsea
+    use w3gdatmd    , only : nx, ny, ungtype, gtype, nseal, nsea, nk
     use w3wdatmd    , only : time
     use w3parall    , only : init_get_isea
     use wav_shr_mod , only : diagnose_mesh, write_meshdecomp, wav_loginit
     use wav_pio_mod , only : wav_pio_init
+#ifdef W3_CESMCOUPLED
+    use wav_shel_inp    , only : set_shel_io
+    use wav_history_mod , only : wav_history_init
+#endif
 #ifdef W3_PDLIB
     use yowNodepool , only : ng
 #endif
@@ -789,6 +796,12 @@ subroutine InitializeRealize(gcomp, importState, exportState, clock, rc)
     integer(i4), pointer         :: meshmask(:)
     integer                      :: iam
     integer                      :: localcomm
+#ifdef W3_CESMCOUPLED
+    type(MPI_COMM)               :: mpicomm
+    integer                      :: mds(15)
+    integer                      :: ntrace(2)
+    character(CL)                :: logfile
+#endif
     character(len=*), parameter  :: subname = '(wav_comp_nuopc:InitializeRealize)'
     ! -------------------------------------------------------------------
 
@@ -814,6 +827,38 @@ subroutine InitializeRealize(gcomp, importState, exportState, clock, rc)
       call wav_pio_init(gcomp, localcomm, stdout, naproc, rc)
       if (ChkErr(rc,__LINE__,u_FILE_u)) return
     end if
+
+    !--------------------------------------------------------------------
+    ! Wave model initialization (deferred from InitializeAdvertise so that
+    ! PIO, set up by the driver after the advertise phase, is available to
+    ! read the netCDF restart in w3init)
+    !--------------------------------------------------------------------
+
+    time = time0
+    call set_shel_io(stdout, mds, ntrace)
+    call ESMF_VMGet(vm, mpiCommunicator=mpicomm%mpi_val, rc=rc)
+    if (ChkErr(rc,__LINE__,u_FILE_u)) return
+    call waveinit_cesm(gcomp, ntrace, mpicomm, mds, rc)
+    if (ChkErr(rc,__LINE__,u_FILE_u)) return
+
+    if ( root_task ) then
+      inquire(unit=stdout, name=logfile)
+      write(*,'(a)')'WW3 log written to '//trim(logfile)
+    end if
+
+    if (wav_coupling_to_cice) then
+      if (nwav_elev_spectrum .gt. nk) then
+        call ESMF_LogWrite('nwav_elev_spectrum is greater than nk ', ESMF_LOGMSG_INFO)
+        call ESMF_Finalize(endflag=ESMF_END_ABORT)
+      end if
+    end if
+
+    ! Intialize the list of requested output variables for netCDF output.
+    ! This needs to occur after mod_def has been read in w3init since
+    ! some variables are available only if they are defined in the mod_def
+    if (use_historync) then
+      call wav_history_init(stdout)
+    end if
 #endif
 
     call ESMF_ClockGet( clock, startTime=startTime, rc=rc)

model/src/wav_history_mod.F90

@@ -522,6 +522,7 @@ subroutine write_history ( timen )
 
     call pio_closefile(pioid)
 
+#ifndef W3_CESMCOUPLED
     ! create indicator log file after NetCDF file is written
     if (iaproc == 1) then   ! only root processor writes the log file
       ! open the log file and write the complete message
@@ -530,6 +531,7 @@ subroutine write_history ( timen )
       call flush(log_unit)
       close(log_unit)
     end if
+#endif
 
   end subroutine write_history