Dear all,

I'm trying to set up a new regional configuration with open boundaries, using release 4.0.5.

After quite some testing some questions remain, for which I hope to get some input from the community. In the following, I try to summarize, what I did so far, what works and what doesn't.

• First of all, installing the code and reproducing the test configuration AMM12 works!

• The new configuration has three strait open boundaries (N,W,S) that I define using the nambdy_index option with automatic definition of the boundary locations by setting nbdyind = -1 in all three nambdy_index. From ocean.output, I see that these boundaries are correctly identified.

• As a first test, I provide constant boundary data (3D U,V,T,S) on the native model grid. These seem to be read. , at least for the western and southern boundaries; there's no print for the northern boundary in ocean.output (independently from the order in which I define the boundaries - it's always the northern that seems to be "silent"; the loop is entered the correct number of times but nothing is printed in the case of the northern boundary). Should I worry about this? If so, what might be going wrong here?

• The velocities are full velocities, so I set ln_full_vel = .true. . Doing so leads to segmentation faults. This seems to be connected to undefined dta_alias%u2d and dta_alias%v2d in SUBROUTINE bdy_dta IF( bf_alias(jp_bdyu3d)%ltotvel ). I can overcome this by setting cn_dyn2d to something else than 'none', although 'none' would be the logical choice, and nn_dyn2d_dta = 0 . Is this a bug or am I misunderstanding something here?

• Furthermore, I'd also like to prescribe SSH but this is not possible with full velocities - correct?

Below are the respective bdy namelists (couldn't find an attache-button).

In the next step, I'd like to use temporally varying boundary conditions, preferably on their own grid. Is this in general implemented? Vertical interpolation seems to work. However I have the impression (from ocean.output, some reading through the code and additionally implemented print-statements, horizontal interpolation - in this case only in one direction, along each boundary - is not implemented. Is this correct? Or in other words: is it mandatory for the boundary conditions to be provided on the same horizontal grid as the model itself?

I've been using NEMO for quite a while now but am new to BDY and appreciate any input that might help to get me through this process.

Best regards, Franziska

!-----------------------------------------------------------------------
&nambdy        !  unstructured open boundaries                          (default: OFF)
!-----------------------------------------------------------------------
   ln_bdy         = .true.                     !  Use unstructured open boundaries
   nb_bdy         = 3                          !  number of open boundary sets
   ln_coords_file = .false.,.false.,.false.    !  =T : read bdy coordinates from file
   cn_coords_file = '','',''                   !  bdy coordinates files
   ln_mask_file   = .false.                    !  =T : read mask from file
   cn_mask_file   = ''                         !  name of mask file (if ln_mask_file=.TRUE.)
   cn_dyn2d       = 'frs','frs','frs'          ! <-- FUS: supposed to be none?
   nn_dyn2d_dta   =  0,0,0                     !  = 0, bdy data are equal to the initial state
   cn_dyn3d      =  'specified','specified','specified'   ! FUS: also tested  'frs','frs','frs' and 'none','none','none' ("closed boundaries")
   nn_dyn3d_dta  =  1,1,1                      !  FUS: 0,0,0 with closed boundaries
   cn_tra        =  'specified','specified','specified'   ! FUS: also tested  'frs','frs','frs' and 'none','none','none' ("closed boundaries")
   nn_tra_dta    =  1,1,1                      !  FUS: 0,0,0 with closed boundaries
   cn_ice        =  'none','none','none'    !
   nn_ice_dta    =  0,0,0         !  = 0, bdy data are equal to the initial state
   ln_tra_dmp    =.false.,.false.,.false.     !  open boudaries conditions for tracers
   ln_dyn3d_dmp  =.false.,.false.,.false.     !  open boundary condition for baroclinic velocities
   rn_time_dmp   =  1,1,1        !  Damping time scale in days
   rn_time_dmp_out = 1,1,1       !  Outflow damping time scale
   nn_rimwidth   = 1,1,1         !  FUS: also tested higher values and 0,0,0
   ln_vol        = .false.    !  total volume correction (see nn_volctl parameter)
   nn_volctl     =  1         !  = 0, the total water flux across open boundaries is zero
/
!-----------------------------------------------------------------------
&nambdy_index   ! index list for open boundaries (added by hand - see NEMO book)
!-----------------------------------------------------------------------
   ctypebdy = 'W'
   nbdyind = -1
   nbdybeg = 0
   nbdyend = 0
/
!-----------------------------------------------------------------------
&nambdy_index   ! index list for open boundaries (added by hand - see NEMO book)
!-----------------------------------------------------------------------
   ctypebdy = 'S'
   nbdyind = -1
   nbdybeg = 0
   nbdyend = 0
/
!-----------------------------------------------------------------------
&nambdy_index   ! index list for open boundaries (added by hand - see NEMO book)
!-----------------------------------------------------------------------
   ctypebdy = 'N'
   nbdyind = -1
   nbdybeg = 0
   nbdyend = 0
/
!!-----------------------------------------------------------------------
&nambdy_dta    !  open boundaries - external data
!-----------------------------------------------------------------------
   ln_zinterp  = .false.      !  T if a vertical interpolation is required. Variables gdep[tuv] and e3[tuv] must exist in the file
   !                          !  automatically defined to T if the number of vertical levels in bdy dta /= jpk
   ln_full_vel = .true.      !  T if [uv]3d are "full" velocities and not only its baroclinic components
   !                          !  in this case, baroclinic and barotropic velocities will be recomputed -> [uv]2d not needed
   !
   cn_dir      = './'    !  root directory for the BDY data location
   !___________!_________________________!___________________!___________!_____________!________!___________!__________________!__________!_______________!
   !           !  file name              ! frequency (hours) ! variable  ! time interp.!  clim  ! 'yearly'/ ! weights filename ! rotation ! land/sea mask !
   !           !                         !  (if <0  months)  !   name    !   (logical) !  (T/F) ! 'monthly' !                  ! pairing  !    filename   !
   bn_ssh      = 'init_fields_l120wonly.nc'  , -12               , 'zos'     , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_u2d      = 'NOT USED'                  , -12               , ''        , .false.     , .true. , 'yearly'  , ''                          ,   ''     ,     ''
   bn_v2d      = 'NOT USED'                  , -12               , ''        , .false.     , .true. , 'yearly'  , ''                          ,   ''     ,     ''
   bn_u3d      = 'init_fields_l120wonly.nc'  , -12               , 'uo'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_v3d      = 'init_fields_l120wonly.nc'  , -12               , 'vo'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_tem      = 'init_fields_l120wonly.nc'  , -12               , 'thetao'  , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_sal      = 'init_fields_l120wonly.nc'  , -12               , 'so'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
/
!-----------------------------------------------------------------------
&nambdy_dta    !  open boundaries - external data
!-----------------------------------------------------------------------
   ln_zinterp  = .false.      !  T if a vertical interpolation is required. Variables gdep[tuv] and e3[tuv] must exist in the file
   !                          !  automatically defined to T if the number of vertical levels in bdy dta /= jpk
   ln_full_vel = .true.      !  T if [uv]3d are "full" velocities and not only its baroclinic components
   !                          !  in this case, baroclinic and barotropic velocities will be recomputed -> [uv]2d not needed
   !
   cn_dir      = './'    !  root directory for the BDY data location
   !___________!_________________________!___________________!___________!_____________!________!___________!__________________!__________!_______________!
   !           !  file name              ! frequency (hours) ! variable  ! time interp.!  clim  ! 'yearly'/ ! weights filename ! rotation ! land/sea mask !
   !           !                         !  (if <0  months)  !   name    !   (logical) !  (T/F) ! 'monthly' !                  ! pairing  !    filename   !
   bn_ssh      = 'init_fields_l120sonly.nc'  , -12               , 'zos'     , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_u2d      = 'NOT USED'                  , -12               , ''        , .false.     , .true. , 'yearly'  , ''                          ,   ''     ,     ''
   bn_v2d      = 'NOT USED'                  , -12               , ''        , .false.     , .true. , 'yearly'  , ''                          ,   ''     ,     ''
   bn_u3d      = 'init_fields_l120sonly.nc'  , -12               , 'uo'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_v3d      = 'init_fields_l120sonly.nc'  , -12               , 'vo'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_tem      = 'init_fields_l120sonly.nc'  , -12               , 'thetao'  , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_sal      = 'init_fields_l120sonly.nc'  , -12               , 'so'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
/
!-----------------------------------------------------------------------
&nambdy_dta    !  open boundaries - external data
!-----------------------------------------------------------------------
   ln_zinterp  = .false.      !  T if a vertical interpolation is required. Variables gdep[tuv] and e3[tuv] must exist in the file
   !                          !  automatically defined to T if the number of vertical levels in bdy dta /= jpk
   ln_full_vel = .true.      !  T if [uv]3d are "full" velocities and not only its baroclinic components
   !                          !  in this case, baroclinic and barotropic velocities will be recomputed -> [uv]2d not needed
   !
   cn_dir      = './'    !  root directory for the BDY data location
   !___________!_________________________!___________________!___________!_____________!________!___________!__________________!__________!_______________!
   !           !  file name              ! frequency (hours) ! variable  ! time interp.!  clim  ! 'yearly'/ ! weights filename ! rotation ! land/sea mask !
   !           !                         !  (if <0  months)  !   name    !   (logical) !  (T/F) ! 'monthly' !                  ! pairing  !    filename   !
   bn_ssh      = 'init_fields_l120nonly.nc'  , -12               , 'zos'     , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_u2d      = 'NOT USED'                  , -12               , ''        , .false.     , .true. , 'yearly'  , ''                          ,   ''     ,     ''
   bn_v2d      = 'NOT USED'                  , -12               , ''        , .false.     , .true. , 'yearly'  , ''                          ,   ''     ,     ''
   bn_u3d      = 'init_fields_l120nonly.nc'  , -12               , 'uo'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_v3d      = 'init_fields_l120nonly.nc'  , -12               , 'vo'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_tem      = 'init_fields_l120nonly.nc'  , -12               , 'thetao'  , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''
   bn_sal      = 'init_fields_l120nonly.nc'  , -12               , 'so'      , .false.     , .true. , 'yearly'  , '' ,   ''     ,     ''