IMPOSED SEA LEVEL AND TIDE. Inversed barometer effect

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flcastej
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Joined: Tue Nov 10, 2009 6:42 pm
Location: Technical University of Cartagena,Murcia, Spain

IMPOSED SEA LEVEL AND TIDE. Inversed barometer effect

#1 Post by flcastej » Wed Jul 15, 2015 1:04 pm

Dear all ROM´s users,

I have been able to run my simulation with tides. I have prepared my tides forcing files and now it´s running without problems. The point is that I will like to add to the tides the inversed barometer effect on the sea level but my working area isn´t enough big to allow the model to reproduce it forcing it with atmospheric pressure data.

I was thinking on calculating the theorical sea level variations due to the IB effect and to force the model with it by a boundary or climatology file. I expect to have some problems forcing the model only with sea level and not with UBAR and VBAR but nowadays I don´t know another way to do so. To clarify it all:

"I will like to add a sea level variation to my tide model using a boundary file or a climatology file"

Any comment or suggestion will be really welcome.

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m.hadfield
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Location: NIWA

Re: IMPOSED SEA LEVEL AND TIDE. Inversed barometer effect

#2 Post by m.hadfield » Thu Jul 16, 2015 5:09 am

You can add non-tidal boundary values to your tidal boundary conditions with the options ADD_FSOBC and ADD_M2OBC. See ROMS/Include/cppdefs.h. The relevant comments in that file say, "use to add tidal elevation/current to processed OBC data". Actually, I think it would more accurate to say "use to add processed OBC data to tidal elevation/current". I.e. these options are needed only when SSH_TIDES and UV_TIDES (respectively) are defined; if you have SSH_TIDES/UV_TIDES without these options you get only tidal forcing. But it you find that confusing or you think I might have got it wrong (or even if you don't) then read the source to see what they do.

johnluick
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Re: IMPOSED SEA LEVEL AND TIDE. Inversed barometer effect

#3 Post by johnluick » Thu Jul 16, 2015 7:20 am

Bear in mind that the ocean adjusts to atmospheric pressure gradients through long waves and currents generated by wind stress. Both pretty easy to model if they are within your domain but you imply your domain is small and you want to model remotely-generated effects to enter at the boundary. Because the pressure system is moving along it is hard to know what sort of water levels and currents to expect at the model boundary, from a system outside the domain. If you look at water levels at a coastal tide gauge you won't generally see the simple hydrostatic "ib effect" (1 cm to -1 mb). In fact in some places the effect is typically not even inverse. (More like the pb effect, "perverse barometer" effect.) Frankly I think you'd have to model the whole domain of the local mesoscale pressure systems and then do what Mark said at your smaller domain boundary.

flcastej
Posts: 68
Joined: Tue Nov 10, 2009 6:42 pm
Location: Technical University of Cartagena,Murcia, Spain

Re: IMPOSED SEA LEVEL AND TIDE. Inversed barometer effect

#4 Post by flcastej » Sun Jul 19, 2015 11:33 am

Dear Marck and John,

Thanks a lot for your answer. Right now I am on holidays so I am not able to check your suggestions. On thursday I will return to the office and test them.

Regards,

-Francisco

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