[MITgcm-devel] tidal forcing

[Ponte, Rui]

Jean-Michel, Dimitris,

This would be a very helpful development. Of course putting in tidal forcing as atmospheric loading was only a quick and easy way of doing it without messing with the model code, but creates several problems as Jean-Michel mentions (another one is that it adds an unphysical signal to bottom pressure).

The best and physically consistent way of treating the tidal forcing is as a horizontal body force in the momentum equations, which I think is what Jean-Michel is proposing. (Jean-Michel…we can talk more at MIT tomorrow if you are around.)

--
Rui

On 10/3/17, 4:06 PM, "Menemenlis, Dimitris (329C)" <Dimitris.Menemenlis at jpl.nasa.gov> wrote:

Jean-Michel, this sounds very useful!
Is Rui on MITgcm Devel list?
It would be good to run your decisions listed below past him.
They are definitely beyond my field of expertise.

(Rui I owe you a response about tides soon.  Sorry right now I am a little overwhelmed.)

D.

> On Oct 3, 2017, at 11:47 AM, Jean-Michel Campin <jmc at mit.edu> wrote:
>
> Hi Dimitris and other,
>
> Until now, when you run some global ocean with tides, the tidal forcing
> was specified as an equivalent atmospheric pressure, presumably through pkg/exf.
>
> There are few limitations with this approach:
> 1) the exf atmospheric pressure field cannot be used for something else,
> such as a more precise estimation of air density (#define EXF_CALC_ATMRHO).
> 2) the tide geopotential is added to the ocean pressure field (totPhiHyd)
> which prevent to use it inside the EOS (selectP_inEOS_Zc=2, default
> with EOS: JMD95P, UNESCO, MDJWF and TEOS10).
> 3) if one want to specify both an atmospheric loading and a tidal forcing,
> the forcing input field become a mix, not practical nor very natural.
> And this is also the case when coupled to atmospheric GCM.
>
> Therefore, I propose to add an other 2-D forcing field to account for
> tidal forcing. The most natural way would be a tidal geopotential (or
> any time-dependent geopotential anomaly), units: m^2/s^2.
>
> An other advantage is that it would be available in the same form for
> Ocean in p-coords set-up as well as for atmospheric set-up.
>
> The gradient of it would be added to horizontal momentum tendency as
> part of the forcing (in S/R EXTERNAL_FORCING_U & EXTERNAL_FORCING_V)
> which is different form current atmospheric loading, for instance regarding
> the Adams-Bashforth (pressure gradient in or out AB depending on staggerTimeStep,
> whereas forcing has it's own parameter: momForcingOutAB).
>
> Any suggestion or comments ?
>
> Cheers,
> Jean-Michel
>
> On Fri, Sep 29, 2017 at 04:41:26PM +0000, Menemenlis, Dimitris (329C) wrote:
>> Jean-Michel and Atanas, two small coupling details that worry me:
>>
>> 1. How do we include tides?  Right now for ocean only simulations
>> we add hourly tidal potential forcing to atmospheric pressure.
>> What is best way to do this in coupled model?
>>
> _______________________________________________
> MITgcm-devel mailing list
> MITgcm-devel at mitgcm.org
> https://urldefense.proofpoint.com/v2/url?u=http-3A__mailman.mitgcm.org_mailman_listinfo_mitgcm-2Ddevel&d=DwIFAg&c=birp9sjcGzT9DCP3EIAtLA&r=1L8uucM1VfjzQOg3MBsQnQ&m=MWPQ4dROdVIcW8QSKD3WvyORP1MSvMAAWtfYvZOrico&s=IsNPMgMYLnxZKgh3QRxIftE_R_2ZdlTNOTztixEmgKg&e=






________________________________

This email is intended solely for the recipient. It may contain privileged, proprietary or confidential information or material. If you are not the intended recipient, please delete this email and any attachments and notify the sender of the error.