Boundary settings are not working for ROMS

[HONGWANG]

Dear all,

There is a problem of the boundary settings (temperature, salinity, velocity) for ROMS model. I ran the model for 3 days and I checked the modelling results with my boundary input.But I found that they are the same only in the intial time. They are very different when the 24th hour, 48 hour, and 72hour (this is the time of the boundary input). It seems that the boundary input dosen't work.

I ran the model for 3 days and used the initial condition and boundary consitions (every day) as:

(1)
LBC(isFsur) == Clo Cha Cha Cha \ ! free-surface
Nes Nes Nes Nes
LBC(isUbar) == CLo Fla Fla Fla \ ! 2D U-momentum
Nes Nes Nes Nes
LBC(isVbar) == Clo Fla Fla Fla \ ! 2D V-momentum
Nes Nes Nes Nes
LBC(isUvel) == Clo RadNud RadNud RadNud \ ! 3D U-momentum
Nes Nes Nes Nes
LBC(isVvel) == Clo RadNud RadNud RadNud \ ! 3D V-momentum
Nes Nes Nes Nes
LBC(isMtke) == Clo Gra Gra Gra \ ! mixing TKE
Nes Nes Nes Nes
LBC(isTvar) == Gra RadNud RadNud RadNud \ ! temperature
Gra RadNud RadNud RadNud \ ! salinity
Nes Nes Nes Nes \
Nes Nes Nes Nes

(2)
ININAME == /home/coawst/Build_COAWST/COAWST/Projects/init_21.nc

NBCFILES == 1
BRYNAME == /home/coawst/Build_COAWST/COAWST/Projects/bdy_21.nc |
/home/coawst/Build_COAWST/COAWST/Projects/bdy_22.nc |
/home/coawst/Build_COAWST/COAWST/Projects/bdy_23.nc |
/home/coawst/Build_COAWST/COAWST/Projects/bdy_24.nc

(3)
and OBCFAC == 0.0d0 Tnudge=0. I think this means that I didn't use the nudging.

For example, for the initial time, modelling results corresponsd well with the initial condition input:


But at the first time (24 hours later) the boundary input (bdy_22):


Anyone knows why at the first input time of the boundaty files, the modelling results are very different from my boundary input? THANK YOU VERY MUCH!

[kate]

and OBCFAC == 0.0d0 Tnudge=0. I think this means that I didn't use the nudging.

What exactly is OBCFAC == 0.0 doing in the code? Perhaps you should check. You are expecting the boundary to be clamped, so why not clamp the salinity boundary? The reason I don't clamp it is that clamping tends to lead to reflections off the boundary. It's a hard problem and we don't have a great solution, but I never expect the model to match the OBC data provided.

[HONGWANG]

Dear Kate,

Thank you very much for your reply! I will test the clamped boundary according to your suggestion. But I have a few problems and still want to consult with you.

(1) In the previous question, I used the RadNud boundaries for the temperature and salinity. But the modelling results at the forcing time difference with my boundaty input files. Is this normal and possible?

(2) Actually, this problem troubles me for a long time. I did lots of tests. For example, I increased or decreased the sea surface salinity by 10% (i.e., 34‰, up tp 37.4‰ or down to 30.6‰) in all the initial and boundary conditions. When I analyzed the modelling results, I found the increase or decreanse of the sea surface salinity only changes a little (i.e., 0.3-0.5 psu ) shown in figure. Is this correct?



I found that both the increased and decreased sea surface salinity (SSS) at a boundary would slowly align with the normal boundary, and not affected by my increased or decresed SSS boundary shown the figure.

I look forward to your reply. Thanks again!

[wilkin]

(3)
and OBCFAC == 0.0d0 Tnudge=0. I think this means that I didn't use the nudging.

If you set the nudging time scale to zero, then yes, the "Nud" part of "RadNud" does nothing. The temp and salt data in your BRYNAME list is ignored. Moreover, even if you had a finite Tnudg your OBCFAC=0 setting would mean that when the Orlanski radiation scheme detects "inflow" (which is when you really want nudging) the obc_in time scale (=obcfac*obc_out) would still be zero.

You have Chapman and Flather schemes for sea level and depth average velocity, so the BRYNAME data for those will be used. Just not the tracers.

[HONGWANG]

I have learned a lot from your reply. And I have did some tests to deepen m understanding of the boundary conditions.
Thank you very much!!