You can run experiments activating surface restoring or Newtonian Dumping (3D nudging). Both feature are already part of NEMO code, nevertheless with auto-ecearth there are some parameters to activate in the configuration files and some variables to take care of in the namelist.

First of all, in both cases, please check that the reference files for your nudged experiments are available on the platform you would like to run. For surface restoring the location is: If you would like to prepare new reference files, their naming should follow the convention :

For 3d nudging, the location is : HSM_DIR/nudging/REFERENCE/CONFIG/fcMEMB/ where REFERENCE is the name of the ocean reanalysis you would like to nudge to ( s4 / glorys2v1 = 2 options available currently ), CONFIG is the ocean model resolution ( ORCA1L75 / ORCA025L75 ) and MEMB is the member. If you would like to prepare new reference files, their naming should follow the convention : REFERENCE_fcMEMB_YYYYMM_grid_T.nc.gz = one file containing 3-dimensional monthly mean temperature and salinity.

SST / SSS restoring

The following model variables can be restored:

  temperature
  salinity

Proj.conf settings: In proj.conf you activate the surface restoring option by putting to TRUE the parameter: SURF_RESTO. You should specify the data towards which you want to restore with : RESTO_DATA. So far you can use oras4, by specifying s4, or a climatology of an experiment you created, by specifying the ID of the experiment. Please note that is responsibility of the user to be sure that the surface restoring data to be used are in the right format and in the right place. In case of doubts speak with Valentina or Yohan.

Namelist settings

You can use nemo-only or coupled version for your nudged experiments. Depending on this the namelist will be standalone or coupled (obvious, but important to remember)

Here is an example to activate SST restoring :

 
   ln_ssr = .true. ! Sea Surface Restoring on T and/or S (T => fill namsbc_ssr)
    &namsbc_ssr    !   surface boundary condition : sea surface restoring
   !-----------------------------------------------------------------------

! filename ! freq ! variable name ! time ! clim ! year or ! weights ! rot ! mask

   !             !                   !       !                ! interp   !          ! monthly   ! filename  ! pair    ! filename
    
   sn_sss      = 'sss_restore_data'  , -1.   , 'so'           , .true.   , .true.  , 'yearly'   , ''        , ''      , ''
   sn_sst      = 'sst_restore_data'  , -1.   , 'thetao'       , .true.   , .true.  , 'yearly'   , ''        , ''      , ''
   sn_msk      = 'mask_restore'      , -12.  , 'mask_ssr'     , .false.  , .true.  , 'yearly'   , ''        , ''      , ''
   !
   cn_dir      = './'    !  root directory for the location of the runoff files  
   nn_sstr     = 1       !  add a retroaction term in the surface heat flux (=1) or not (=0)
   nn_sssr     = 2       !  add a damping term in the surface freshwater flux (=2) or to SSS only (=1) or no damping term (=0)
   nn_icer     = 0       !  perform sea surface restoring (=1) or not (=0) where there is sea-ice
   nn_msk      = 1       !  add a sub-regional masking to the surface restoring (=1) or not (=0)
                       !  sn_msk can be empty if nn_msk = 0
   rn_dqdt     = -40.    !  magnitude of the retroaction on temperature   [W/m2/K]
   rn_deds     = -166.67 !  magnitude of the damping on salinity   [kg/m2/s/psu]
   ln_sssr_bnd = .false.  ! .true. !  flag to bound erp term (associated with nn_sssr=2)
   rn_sssr_bnd = 4.e0    !  ABS(Max/Min) value of the damping erp term [mm/day]
   /

!———————————————————————–

Reference data Nudging files, as defined in fldread.F90. They can be one file per year (even if there are one record per month in it), or one separate file for each and every month. In the following example it's one file with 12 months, for each variable.

Note that the name of the file contains “_yXXXX” where XXXX are the 4 digit of the year.

sst_data_yXXXX.nc sss_data_yXXXX.nc

SST parameters :

nn_sstr

sn_sst

file name : Name of the nudging file, as defined in fldread.F90, without the year suffix and the .nc

frequency : the frequency of the data, usually 1 month, i.e. -1

variable name : the variable name in the nudging file

time interpol. : the nudging is usually done once a day, so unless you have hourly data, you'll want the model to interpolate your monthly data

clim : put this to .true., if you use climatological instead of interannual data

'yearly'/'monthly' : do you have one file per year (even if there are one record per month in it), or one separate file for each and every month

weights filename : this is used only when your data is not already on the ORCA2 grid, to spatially interpolate it during the run

rotation pairing : in case you have to spatially interpolate vectors

rn_dqdt (-40 W/m2/K is the standard value based on physical considerations)

SSS parameters :

nn_sssr sn_sss : same as above rn_deds (-864 mm/day/psu is the standard value consistent with rn_dqdt = -40)

The user must create the nudging files, according to experiment needs. These files can be created either all the once at the beginning of the simulation or after each leg during the simulation. The script to create such files will be uploaded here soon.

The user can activate SST restoring and SSS restoring independently with nn_sstr and nn_sssr

To switch it on, just add nemo:oceanudg2d to your config variable at the top of the template script in the runtime/classic directory. You will need to add/link the nudging files to your run directory, as described below.

Please note that this is an ongoing work. At BSC we work on this development with the branch bsc_nemo_nudging. No changes have been so far in classic. For further informations contact valentina.sicardi@bsc.es