I’m running ROMS in barotropic mode only forced by tides. The results are actually quite good for all validated constituents (surface and current) except for the current-ellipses of O1 in one area. In this area the modeled O1 current ellipses is up to five times too large (see Figure 1 below). The only other thing which seems suspicious is that the diurnal constituents seem to be somewhat out of sync with the forcing (see Figure 2 below). Beginning right inside the boundary, the modeled diurnal constituents (surface amplitude) are about one cm too large compared to the forcing and some boundary features are shifted somewhat. Similar behavior is not observed for the semi-diurnal constituents.

Here is what I have tried so far without getting rid of the problem:

Changing tunable parameters:

- Quadratic friction (rdrg) form 2*10^-3 to 3*10^-3

- Horizontal viscosity coefficient (visc2) from 200 to 20

Changing the forcing

- Run with surface forcing only

- Run with surface and current forcing

- Run with forcing from OSU tidal data inversion Atlantic model/domain

- Run with forcing from OSU tidal data inversion Global model/domain

Change the propagation dynamics

- Run with nonlinear advection terms

- Run without nonlinear advection terms

I’ve had some theories on what could be the cause, but now there are almost none left. Since this is my first ROMS application there is always the possibility that I’ve done some stupid mistake . . . see the first part of the log file below.

**Question:**

Is there any other parameter which could influence the results such as nudging/relaxation settings of Znudg, M2nudg, obcfac or others???

p.s. the model is first run for 10 days with any given settings before data are stored, so start-up effects should not be an issue.

Beginning of log-file:

. . .

Physical Parameters, Grid: 01

=============================

Code: Select all

```
1920000 ntimes Number of timesteps for 3-D equations.
1.800 dt Timestep size (s) for 3-D equations.
1 ndtfast Number of timesteps for 2-D equations between
each 3D timestep.
1 ERstr Starting ensemble/perturbation run number.
1 ERend Ending ensemble/perturbation run number.
0 nrrec Number of restart records to read from disk.
T LcycleRST Switch to recycle time-records in restart file.
6000 nRST Number of timesteps between the writing of data
into restart fields.
200 ninfo Number of timesteps between print of information
to standard output.
T ldefout Switch to create a new output NetCDF file(s).
1000 nHIS Number of timesteps between the writing fields
into history file.
24000 ndefHIS Number of timesteps between creation of new
history files.
2.0000E+01 nl_visc2 NLM Horizontal, harmonic mixing coefficient
(m2/s) for momentum.
0.0000E+00 rdrg Linear bottom drag coefficient (m/s).
2.5000E-03 rdrg2 Quadratic bottom drag coefficient.
0.0000E+00 Zob Bottom roughness (m).
1025.000 rho0 Mean density (kg/m3) for Boussinesq approximation.
0.000 dstart Time-stamp assigned to model initialization (days).
0.000 tide_start Reference time origin for tidal forcing (days).
20100101.00 time_ref Reference time for units attribute (yyyymmdd.dd)
0.0000E+00 Znudg Nudging/relaxation time scale (days)
for free-surface.
0.0000E+00 M2nudg Nudging/relaxation time scale (days)
for 2D momentum.
2.0000E+01 obcfac Factor between passive and active
open boundary conditions.
1.000 gamma2 Slipperiness variable: free-slip (1.0) or
no-slip (-1.0).
T Hout(idFsur) Write out free-surface.
T Hout(idUbar) Write out 2D U-momentum component.
T Hout(idVbar) Write out 2D V-momentum component.
Output/Input Files:
Output Restart File: faroegrid1_rst_nof.nc
Prefix for History Files: faroegrid1_his_nof
Input Grid File: FaroeIslandsGrid1_grd.nc
Tile partition information for Grid 01: 1403x0731 tiling: 004x001
tile Istr Iend Jstr Jend Npts
0 1 351 1 731 256581
1 352 702 1 731 256581
2 703 1053 1 731 256581
3 1054 1403 1 731 255850
Tile minimum and maximum fractional grid coordinates:
(interior points only)
tile Xmin Xmax Ymin Ymax grid
0 -0.50 1404.50 -0.50 732.50 RHO-points
1 -0.50 1404.50 -0.50 732.50 RHO-points
2 -0.50 1404.50 -0.50 732.50 RHO-points
3 -0.50 1404.50 -0.50 732.50 RHO-points
0 -0.50 1404.50 -0.50 732.50 U-points
1 -0.50 1404.50 -0.50 732.50 U-points
2 -0.50 1404.50 -0.50 732.50 U-points
3 -0.50 1404.50 -0.50 732.50 U-points
0 -0.50 1404.50 -0.50 732.50 V-points
1 -0.50 1404.50 -0.50 732.50 V-points
2 -0.50 1404.50 -0.50 732.50 V-points
3 -0.50 1404.50 -0.50 732.50 V-points
Activated C-preprocessing Options:
FAROEGRID1 2D-tidal model Faroe area grid 1 (grid: 1405x733, res.:500mx500m)
ADD_FSOBC Adding tidal elevation to proccesed OBC data.
ANA_FSOBC Analytical free-surface boundary conditions.
ANA_INITIAL Analytical initial conditions.
ANA_M2OBC Analytical 2D momentum boundary conditions.
ANA_SMFLUX Analytical kinematic surface momentum flux.
ASSUMED_SHAPE Using assumed-shape arrays.
DOUBLE_PRECISION Double precision arithmetic.
EAST_FSCHAPMAN Eastern edge, free-surface, Chapman condition.
EAST_M2FLATHER Eastern edge, 2D momentum, Flather condition.
FSOBC_REDUCED Using free-surface data in reduced physics condtions
MASKING Land/Sea masking.
NONLINEAR Nonlinear Model.
NORTH_FSCHAPMAN Northern edge, free-surface, Chapman condition.
NORTH_M2FLATHER Northern edge, 2D momentum, Flather condition.
_OPENMP OpenMP parallel shared-memory directives.
PROFILE Time profiling activated .
RAMP_TIDES Ramping tidal forcing for one day.
!RST_SINGLE Double precision fields in restart NetCDF file.
SOUTH_FSCHAPMAN Southern edge, free-surface, Chapman condition.
SOUTH_M2FLATHER Southern edge, 2D momentum, Flather condition.
SSH_TIDES Add tidal elevation to SSH climatology.
UV_COR Coriolis term.
UV_QDRAG Quadratic bottom stress.
UV_VIS2 Harmonic mixing of momentum.
WEST_FSCHAPMAN Western edge, free-surface, Chapman condition.
WEST_M2FLATHER Western edge, 2D momentum, Flather condition.
INITIAL: Configuring and initializing forward nonlinear model ...
Minimum X-grid spacing, DXmin = 4.92730546E-01 km
Maximum X-grid spacing, DXmax = 5.05848297E-01 km
Minimum Y-grid spacing, DYmin = 4.92359303E-01 km
Maximum Y-grid spacing, DYmax = 5.06168304E-01 km
Minimum barotropic Courant Number = 3.36906469E-02
Maximum barotropic Courant Number = 9.61345517E-01
Maximum Coriolis Courant Number = 2.37022567E-04
GET_NGFLD - tidal period
(Min = 4.30820453E+04 Max = 2.38068000E+06)
GET_2DFLD - tidal elevation amplitude
(Min = 0.00000000E+00 Max = 9.73707845E-01)
GET_2DFLD - tidal elevation phase angle
(Min = 1.14436078E-03 Max = 6.28303696E+00)
Initial basin volumes: TotVolume = 1.2274133756E+14 m3
MinVolume = 1.1040633569E+06 m3
MaxVolume = 9.0342023445E+08 m3
Max/Min = 8.1826847053E+02
NL ROMS/TOMS: started time-stepping: (Grid: 01 TimeSteps: 00000001 - 01920000)
```