[MITgcm-support] tidal forcing and wind forcing
Himansu Pradhan
oceancalling at gmail.com
Sat Sep 6 12:47:18 EDT 2014
Thank you all for your suggestion. It has increased my understanding
regarding the subject.
@ Jody : They (EXP_1 and EXP_2) are exactly the same .
I feel i have given the tidal forcing too high.i.e. something like this :
gU(i,j,kLev,bi,bj) = gU(i,j,kLev,bi,bj)
& +6*(0.29)*(0.0001406810036)*cos(0.0001406810036*myTime) - M2
& +6*(0.3) *(0.0001453703704)*cos(0.0001453703704*myTime) - S2
& +4*(0.15)*(0.0000728978038)*cos(0.0000728978038*myTime) - K1
& +4*(0.14)*(0.0000675643691)*cos(0.0000675643691*myTime) - O1
The factors 6,6,4,4 is multiplied - so that both model and the observations
(of my region/basin) have same amplitude ( density/velocity oscillations).
As per your suggestation i have simulated with less magnitude of tidal
forcings ( dropped the factors 6,6,4,4) , but the amplitudes i get are 5-6
times smaller.
@ Dimitris : I have provided tidal forcing in code/external_Forcing.F as it
was a bit easier comapred to its counterpart (using open bounday horizontal
velocity (OPHV) forcings). In OPHV forcing, velocity at all the vertical
levels are unknown to me in an open ocean and also large number of files
are to be made for 30-50 days simulation. I have never tried to force the
model with "surface atmospheric pressure".
Hoping to get more suggestion/advice.
On Thu, Sep 4, 2014 at 9:13 PM, Jody Klymak <jklymak at uvic.ca> wrote:
> 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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>
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