[MITgcm-support] tidal forcing and wind forcing

[Jody Klymak]

Hi Himansu,

On Sep 4, 2014, at  3:24 AM, Himansu Pradhan <oceancalling at gmail.com> wrote:

> I am giving tidal forcing to the model in  code/external_forcing.F in its momentum equations i.e. by adding tidal forcing terms to "gU" and "gV". Thus the model simulations shows oscillations in tidal frequency in the density/velocity field representing internal waves. This is fine.  (say EXP_1)
> 
> But, when i prescribe "wind stress" to the model (in input/data.exf) along with the background tidal forcing (in code/external_forcing.F) , the simulations give the effect only due to tide (say EXP_2). The wind driven circulation is not represented  in the output ???  The model results for EXP_1 and EXP_2 are same !!!!!!
> 
> 
So when you say "the same" do you mean exactly the same or pretty close?  If the latter I'd suspect the strength of one of your forcings is too high or too low.  If the former, then I wonder if you have made an error in "adding" gU and gV, ie. you don't actually add them, but simply overwrite them?

With regards to Dimitris' suggestion, I've forced both ways to good effect, so I think its possible to do the tides with a body forcing.  You just need to make sure you calculate how strong that force should be correctly.  Its pretty easy to drop or add a factor of g, H, 1000, or 2pi/omega!  for your tide-only run, "oscillations in tidal frequency" is vague.  Are the tides reasonable for your basin?  If your depth averaged currents are 1 m/s in a 4000-m deep basin (for example), thats not "reasonable".

Cheers,  Jody


> note:
> 
> (i) to see the wind driven circulation i average velovity field for 5 to 7 days. 
> 
> 
> 
> (ii) The wind driven circulation is very well represented daily and monthly basis  ( when daily/monthly winds are given as input to the model) , when tidal forcing are not added in the momentum equations.
> 
> 
> 
> Himansu
> 
> India
> 
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--
Jody Klymak    
http://web.uvic.ca/~jklymak/





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