do i have to add the UV_TIDES for a real case?

[wuhe]

hi, dear all!
If I want to run a simulation of tide of a real case, do I have to add the harmonic constants of current(UV_TIDES) to the open boundary, in other words,If I only add the SSH_TIDES to the boundary, can it simulate well enough?
the cpp of my simulation as followed, although it runs well, its result is too bad! is there anything wrong? please help me!

#define UV_ADV /* use to turn ON or OFF advection terms */
#define CURVGRID
#define UV_COR /* use to turn ON or OFF Coriolis term */
#define UV_QDRAG /* use to turn ON or OFF quadratic bottom friction */
#define UV_VIS2 /* use to turn ON or OFF harmonic horizontal mixing */
#define MIX_S_UV /* momentum mixing on s-surfaces */
#define DJ_GRADPS /* use if splines density Jacobian (Shchepetkin, 2000) */
#define TS_U3HADVECTION /* use if 3rd-order upstream horiz. advection */
#define TS_C4VADVECTION /* use if 4th-order centered vertical advection */


#define SPLINES /* use to activate parabolic splines reconstruction */
#define WET_DRY
#define ANA_SMFLUX /* use if analytical surface momentum stress */

#define MASKING /* use if analytical masking is enabled */
#define ANA_INITIAL

#define EAST_FSCHAPMAN /* use if free-surface Chapman condition*/
#define EAST_M3GRADIENT
#define RAMP_TIDES
# define EAST_M2FLATHER

#define SSH_TIDES

#ifdef SSH_TIDES
# define ADD_FSOBC
# define FSOBC_REDUCED
#endif

[kate]

Some of us who model tides use the Oregon State product (http://volkov.oce.orst.edu/tides/) to get boundary conditions. This includes both currents and elevation.

If you aren't getting good tides with just the elevation, there's more than one potential reason, depending. Perhaps if you describe what you are doing and what you are seeing?

[m.hadfield]

The best solution, if you have velocity data, is to use SSH_TIDES, UV_TIDES, *_M2FLATHER and *_FSCHAPMAN.

In principle, the combination of SSH_TIDES, *_M2REDUCED and *_FSCLAMPED should work with some situation-dependent loss of accuracy because of the missing velocity data. However on large domains I find M2REDUCED boundary conditions prone to runway behaviour related, I think, to the Coriolis force.

I find the FSOBC_REDUCED code confusing and the results not what I expect, but perhaps that's just me.

Please share your experience with us and perhaps we can all learn.

[wuhe]

thanks! kate,
i am sorry that OPTS data is not corret, especially elevation phase. for example, Ephase of m2, to my knowleage, is 300 degree on the channel of china bohai sea, and about 50 in the OPTS data. so i am not sure about the accuracy of current hamornic constants.
thanks! hadfield,
i maybe i should compare the OBC codes between ROMS and ECOM, latter can simulate china sea very well only by HC of elevation, if i have some new, i will share them.

[hetland]

I think it is important to understand if you have a propagating or standing wave. Usually, this boils down to large vs. small domains, respectively. I usually just specify sea-level on my boundaries for small domains, since the tides at my boundaries have both the incoming and outgoing waves in approximately equal parts.

If you use a Flather condition to specify ssh only with a propagating wave, you will only get half of the wave you expect. Using reduced physics might help this a bit, but you should do some experiments to be sure.

[mengqingjun]

If you use a Flather condition to specify ssh only with a propagating wave, you will only get half of the wave you expect. Using reduced physics might help this a bit, but you should do some experiments to be sure.

I am running a real case which only has the tidal forcing with M2,S2,K1,O1;I provide ROMS with the tidal constituents at all grid points and to have ROMS reconstruct the tidal currents. The tidal constituents tide_perios, tide_Eamp, tide_Ephase, tide_Cangle, tide_Cphase,tide_Cmax, tide_Cmin are computed from TPXO6.nc.
What I used in .h file are: #define SSH_TIDES #define UV_TIDES #define ADDFSOBC #define ADDM2OBC ,and I used ANA_SMFLUX,ANA_STFLUX,ANA_SSFLUX,ANA_BTFLUX,ANA_BSFLUX.
I used #define UV_QDARG and the I set RDRG2 == 3.0d-03 ! nondimensional.
I provide ROMS with bry.nc file with zeta,ubar,vbar,u,v at all boundaies are zero with 90 time records; I run my case for 90 days and output zeta every 1 hour.The boundary conditions I set in the ocean.in file are:

LBC(isFsur) == Cha Cha Cha Cha
LBC(isUbar) == Fla Fla Fla Fla ! 2D U-momentum
LBC(isVbar) == Fla Fla Fla Fla ! 2D V-momentum
LBC(isUvel) == RadNud RadNud RadNud RadNud ! 3D U-momentum
LBC(isVvel) == RadNud RadNud RadNud RadNud ! 3D V-momentum
LBC(isMtke) == Gra Gra Gra Gra ! mixing TKE

LBC(isTvar) == RadNud RadNud RadNud RadNud \ ! temperature
RadNud RadNud RadNud RadNud ! salinity

I also set lateral open boundary edge volume conservation switch "T":

VolCons(west) == T ! western boundary
VolCons(east) == T ! eastern boundary
VolCons(south) == T ! southern boundary
VolCons(north) == T ! northern boundary

I make harmonic analysis wiht ROMS output zeta using t_tide and find that the amplitude of M2 is too small !!I think it only has half of the amplitude. Actually I find that the ROMS output zeta is also small. Why ?
Anyone who could give me some advices ?

[kate]

Try again with the VolCons options set to false.

Also, you might try to change the Cha, Fla options to the new Che, Shc options for LBC, but I think this will be a smaller change.

[mengqingjun]

Thank you Kate very much. It really helps !