Some questions about water transport at OBC

[chysun]

Hi all,
I have some doubts about water transport at OBC when imposing tides. Hopes I can get some tips here.

1.Does topography cut off contribute the inaccuracy of water transport especially at OBC which water goes in and out and how do we deal with it if it does?
ROMS needs a topography cut off to ensure it wont blow up. But it seems to lead an inaccurate water transport when we have velocity at OBC provided by other models. Is it acceptable?

2.Does sponge layer contribute the inaccuracy of water transport and how do we deal with it if it does?
If I run a tidal case only, a sponge layer would decrease the tidal velocity and this is not good for my case---correct me if I am wrong.


Any comments is appreciated!

Thanks in advance,
Haiyun

[kate]

Hi all,
I have some doubts about water transport at OBC when imposing tides. Hopes I can get some tips here.

1.Does topography cut off contribute the inaccuracy of water transport especially at OBC which water goes in and out and how do we deal with it if it does?
ROMS needs a topography cut off to ensure it wont blow up. But it seems to lead an inaccurate water transport when we have velocity at OBC provided by other models. Is it acceptable?

Only you can answer that for your application.

2.Does sponge layer contribute the inaccuracy of water transport and how do we deal with it if it does?
If I run a tidal case only, a sponge layer would decrease the tidal velocity and this is not good for my case---correct me if I am wrong.

If by "sponge" you mean increased viscosity near the boundary, I have never found that to be particularly helpful. I don't use the SPONGE in ROMS lingo. However, at least one other modeling community says "sponge" when they mean nudging to an external climatology near the boundary. I have done this many a time - to reduce along-boundary currents.

[chysun]

Hi Kate,
Thanks for your comments! Forgive me for not having knowledge of ROMS lingo.
I get those doubts when I try to figure out why ROMS tidal elevation is about 20% below the insitu data in my tidal case. Some parameters like surface/bottom roughness, drag coefficient, may relate to my problem but I am not quite sure. Would you please share some experience on tidal elevation adjusting?

Thanks in advance,
Haiyun

[kate]

My experience can be summed up with "trial and error". Someone smarter would use inverse theory to set up a minimization problem involving the spatially varying bottom drag or some such thing.