unrealistic boundary current when modeling internal tide
unrealistic boundary current when modeling internal tide
Dear all,
I am modeling the M2 internal tide in South China Sea (the domain could be seen in the following figure). The only forcing I used is tidal forcing, which is derived from TPXO7.1. The _FSChapman, _M2Flather, _M3Radiation and _TSRadiation OBCs are applied at all of the four open boundaries. The initial T/S are horizontally uniform, so there should be no geostrophic currents in the initial fields.
My problem is that after several days of simulation, some strong currents appear at the open boundaries. The first figure is the daily averaged surface layer temperature and velocity field at the 10th day, while the second is the surface layer daily averaged temperature and velocity field at the 30th day.
Do you have any idea about where these “unrealistic” boundary currents originate from? Thanks in advance.
Kun
I am modeling the M2 internal tide in South China Sea (the domain could be seen in the following figure). The only forcing I used is tidal forcing, which is derived from TPXO7.1. The _FSChapman, _M2Flather, _M3Radiation and _TSRadiation OBCs are applied at all of the four open boundaries. The initial T/S are horizontally uniform, so there should be no geostrophic currents in the initial fields.
My problem is that after several days of simulation, some strong currents appear at the open boundaries. The first figure is the daily averaged surface layer temperature and velocity field at the 10th day, while the second is the surface layer daily averaged temperature and velocity field at the 30th day.
Do you have any idea about where these “unrealistic” boundary currents originate from? Thanks in advance.
Kun
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Re: unrealistic boundary current when modeling internal tide
What does your bathymetry look like? What is the source of it and did you smooth it at all?
Re: unrealistic boundary current when modeling internal tide
Hi Kate, the bathymetry in my model (see the following figure) is derived from etopo2, with the horizontal resolution as 1/20*1/20 degree. And it is smoothed with the max slope parameter (r=grad(h)/h) as 0.25.kate wrote:What does your bathymetry look like? What is the source of it and did you smooth it at all?
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Re: unrealistic boundary current when modeling internal tide
Hi Kun,
I ran into a similar problem when trying to model internal tides on the Australian north west shelf. I was setting up the model using the same methodology (horizontally uniform TS). I found that you also need to set _TNUDGING and _M3NUDGING to constrain the tracers and baroclinic velocities at the boundaries when using the radiation conditions. You will also need to set the nudging time scales parameters in the *.in file.
I used:
TNUDG == 60.0d0 60.0d0
M3NUDG == 60.0d0
and
OBCFAC == 60.0d0
I was nudging the M3 to zero and TS back to the initial conditions at the boundaries.
Matt
I ran into a similar problem when trying to model internal tides on the Australian north west shelf. I was setting up the model using the same methodology (horizontally uniform TS). I found that you also need to set _TNUDGING and _M3NUDGING to constrain the tracers and baroclinic velocities at the boundaries when using the radiation conditions. You will also need to set the nudging time scales parameters in the *.in file.
I used:
TNUDG == 60.0d0 60.0d0
M3NUDG == 60.0d0
and
OBCFAC == 60.0d0
I was nudging the M3 to zero and TS back to the initial conditions at the boundaries.
Matt
Re: unrealistic boundary current when modeling internal tide
Hi Matt, thanks a lot for your suggestion. I tried out your method. It is a good way to constrain the model. The boundary currents are reduced, however, not completely vanished. Do you have any idea about the source of these currents? I believe only if we know where this problem comes from, could it be fully solved.mrayson wrote:Hi Kun,
I ran into a similar problem when trying to model internal tides on the Australian north west shelf. I was setting up the model using the same methodology (horizontally uniform TS). I found that you also need to set _TNUDGING and _M3NUDGING to constrain the tracers and baroclinic velocities at the boundaries when using the radiation conditions. You will also need to set the nudging time scales parameters in the *.in file.
I used:
TNUDG == 60.0d0 60.0d0
M3NUDG == 60.0d0
and
OBCFAC == 60.0d0
I was nudging the M3 to zero and TS back to the initial conditions at the boundaries.
Matt
Best,
Kun
Be Good, Do Right!
Re: unrealistic boundary current when modeling internal tide
Could you tell us the CPPs you used in your model?
Re: unrealistic boundary current when modeling internal tide
Hi feroda, the CPP options I activated are:feroda wrote:Could you tell us the CPPs you used in your model?
Code: Select all
ADD_FSOBC Adding tidal elevation to proccesed OBC data.
ADD_M2OBC Adding tidal currents to proccesed OBC data.
ANA_BSFLUX Analytical kinematic bottom salinity flux.
ANA_BTFLUX Analytical kinematic bottom temperature flux.
ANA_FSOBC Analytical free-surface boundary conditions.
ANA_M2OBC Analytical 2D momentum boundary conditions.
ANA_SMFLUX Analytical kinematic surface momentum flux.
ANA_SSFLUX Analytical kinematic surface salinity flux.
ANA_STFLUX Analytical kinematic surface temperature flux.
ASSUMED_SHAPE Using assumed-shape arrays.
AVERAGES Writing out time-averaged fields.
DIFF_GRID Horizontal diffusion coefficient scaled by grid size.
DJ_GRADPS Parabolic Splines density Jacobian (Shchepetkin, 2002).
DOUBLE_PRECISION Double precision arithmetic.
EAST_FSCHAPMAN Eastern edge, free-surface, Chapman condition.
EAST_M2FLATHER Eastern edge, 2D momentum, Flather condition.
EAST_M3NUDGING Eastern edge, 3D momentum, passive/active outflow/inflow.
EAST_M3RADIATION Eastern edge, 3D momentum, radiation condition.
EAST_TNUDGING Eastern edge, tracers, passive/active outflow/inflow.
EAST_TRADIATION Eastern edge, tracers, radiation condition.
MASKING Land/Sea masking.
MIX_GEO_TS Mixing of tracers along geopotential surfaces.
MIX_S_UV Mixing of momentum along constant S-surfaces.
MPI MPI distributed-memory configuration.
NONLINEAR Nonlinear Model.
NONLIN_EOS Nonlinear Equation of State for seawater.
NORTH_FSCHAPMAN Northern edge, free-surface, Chapman condition.
NORTH_M2FLATHER Northern edge, 2D momentum, Flather condition.
NORTH_M3NUDGING Northern edge, 3D momentum, passive/active outflow/inflow.
NORTH_M3RADIATION Northern edge, 3D momentum, radiation condition.
NORTH_TNUDGING Northern edge, tracers, passive/active outflow/inflow.
NORTH_TRADIATION Northern edge, tracers, radiation condition.
POWER_LAW Power-law shape time-averaging barotropic filter.
PROFILE Time profiling activated .
RADIATION_2D Use tangential phase speed in radiation conditions.
RAMP_TIDES Ramping tidal forcing for one day.
!RST_SINGLE Double precision fields in restart NetCDF file.
SALINITY Using salinity.
SOLVE3D Solving 3D Primitive Equations.
SOUTH_FSCHAPMAN Southern edge, free-surface, Chapman condition.
SOUTH_M2FLATHER Southern edge, 2D momentum, Flather condition.
SOUTH_M3NUDGING Southern edge, 3D momentum, passive/active outflow/inflow.
SOUTH_M3RADIATION Southern edge, 3D momentum, radiation condition.
SOUTH_TNUDGING Southern edge, tracers, passive/active outflow/inflow.
SOUTH_TRADIATION Southern edge, tracers, radiation condition.
SPLINES Conservative parabolic spline reconstruction.
SSH_TIDES Add tidal elevation to SSH climatology.
TS_U3HADVECTION Third-order upstream horizontal advection of tracers.
TS_C4VADVECTION Fourth-order centered vertical advection of tracers.
TS_DIF2 Harmonic mixing of tracers.
UV_ADV Advection of momentum.
UV_COR Coriolis term.
UV_U3HADVECTION Third-order upstream horizontal advection of 3D momentum.
UV_C4VADVECTION Fourth-order centered vertical advection of momentum.
UV_QDRAG Quadratic bottom stress.
UV_TIDES Add tidal currents to 2D momentum climatologies.
UV_VIS2 Harmonic mixing of momentum.
VAR_RHO_2D Variable density barotropic mode.
VISC_GRID Horizontal viscosity coefficient scaled by grid size.
WEST_FSCHAPMAN Western edge, free-surface, Chapman condition.
WEST_M2FLATHER Western edge, 2D momentum, Flather condition.
WEST_M3NUDGING Western edge, 3D momentum, passive/active outflow/inflow.
WEST_M3RADIATION Western edge, 3D momentum, radiation condition.
WEST_TNUDGING Western edge, tracers, passive/active outflow/inflow.
WEST_TRADIATION Western edge, tracers, radiation condition.
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Re: unrealistic boundary current when modeling internal tide
Have you ever tried to run the model without tidal forcing under same condition?
Re: unrealistic boundary current when modeling internal tide
The tidal forcing is the only forcing I used in my model. The ocean will stay at rest if the tidal forcing is removed,susonic wrote:Have you ever tried to run the model without tidal forcing under same condition?
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Re: unrealistic boundary current when modeling internal tide
Have you tested that the ocean actually remains at rest when unforced? I had huge problems when simulating motionless stratified unforced water in a bounded region with sloping bathymetry. Artificial currents where generated near sloping sigmalayers.
Re: unrealistic boundary current when modeling internal tide
Actually, I am pretty curious of your model domain. Comparing tidal currents with topography, it is obvious that the currents largely follow the steep bathymetry slop. Why don't you expand your western boundary to southeast coast of China? It is also worthwhile to think about if you want to include the Taiwan Strait, as the tidal currents there might be stronger than those in your present model domain.