[MITgcm-support] Tides in channel model

Mon Dec 6 11:42:22 EST 2021

Thank you Stanislav, Ryan, Yu-Kun, Jody and Jean-Michel for the help! I
think these are all very helpful suggestions. As some of you mentioned EXF,
I want to ask a follow up question about this package: what kind of input
file it's expecting for tidal forcing? I couldn't find an answer to this
from the MITGCM's user manual.

Thanks,
Qiyu

On Sat, Dec 4, 2021 at 12:00 PM <mitgcm-support-request at mitgcm.org> wrote:

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> Today's Topics:
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>    1. Re: Tides in channel model (Jody Klymak)
>    2. Re: Tides in channel model (Jean-Michel Campin)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 3 Dec 2021 18:13:26 +0100
> From: Jody Klymak <jklymak at uvic.ca>
> To: mitgcm-support at mitgcm.org
> Subject: Re: [MITgcm-support] Tides in channel model
> Message-ID: <2743C27F-C1CB-4AF0-82E2-D0E698F5FB5A at uvic.ca>
> Content-Type: text/plain; charset="utf-8"
>
> I hesitate to share this because it is undocumented, but it works fine:
>
>
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_jklymak_MITgcm-5Fbtforcing&d=DwICAg&c=slrrB7dE8n7gBJbeO0g-IQ&r=5BDRdcOUIuLA0nIj7UBsNw&m=y1zd1j4BNqJV66mCcYi5svvmGr5gN1TgbfQ3HsncVPj6iFSQzQVtU6RZ1_TgDGnk&s=LJ77rs2ArlyEBb2sDDFurZt3ZkLqzPnP0k7HBucDYD4&e=
> <
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_jklymak_MITgcm-5Fbtforcing&d=DwICAg&c=slrrB7dE8n7gBJbeO0g-IQ&r=5BDRdcOUIuLA0nIj7UBsNw&m=y1zd1j4BNqJV66mCcYi5svvmGr5gN1TgbfQ3HsncVPj6iFSQzQVtU6RZ1_TgDGnk&s=LJ77rs2ArlyEBb2sDDFurZt3ZkLqzPnP0k7HBucDYD4&e=
> >
>
> You should definitely adapt to your needs, - this one forces in y by fU
> for a mean, and x by a tidal body force?
>
>
> Cheers,  Jody
>
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>
> ------------------------------
>
> Message: 2
> Date: Fri, 3 Dec 2021 12:28:28 -0500
> From: Jean-Michel Campin <jmc at mit.edu>
> To: mitgcm-support at mitgcm.org
> Subject: Re: [MITgcm-support] Tides in channel model
> Message-ID: <20211203172828.GB46701 at ocean.mit.edu>
> Content-Type: text/plain; charset=us-ascii
>
> Hi Ryan,
>
> Since the tidal forcing is just variation of gravity, and gravity can be
> expressed
> as gradient of a potential, the tidal forcing can be provided as a tidal
> potential.
> This is how it's done in MITgcm, except that it's only a 2-D forcing field
> (neglecting vertical
> gradient of tidal geopotential is generally OK and fits better with
> hydrostatic approximation
> and, to a lesser extent with thin-shell approximation).
>
> It has been implemented in pkg/exf (back in October 2017):
> #define EXF_ALLOW_TIDES , variable "tidePot", parameters "tidePot*" (e.g.,
> tidePotFile, tidePotStartdate1 ...).
>
> And I am copying below the content of a message that got sent to some
> MITgcm email list
> back at that time, regarding the advantage of separating tidal
> geopotential from
> atmospheric pressure loading.
>
> Cheers,
> Jean-Michel
>
> -------------------------
> > Tue Oct 3 14:47:22 EDT 2017
> >
> > 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, Dec 03, 2021 at 11:46:58PM +0800, ?????? wrote:
> > Hi Ryan,
> >
> >
> > I have recently tried to add a body forcing to mimic the M2 tide
> > in a channel model (in 2D x-z plane).  It is quite easy to implement
> > this by adding some code snippets in 'apply_forcing.F' (see attached).
> > I found these codes somewhere on the web (but do not remember now).
> > Its effect can be seen in this animation:
> >
> https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_miniufo_InternalWaveBreaking&d=DwICAg&c=slrrB7dE8n7gBJbeO0g-IQ&r=5BDRdcOUIuLA0nIj7UBsNw&m=y1zd1j4BNqJV66mCcYi5svvmGr5gN1TgbfQ3HsncVPj6iFSQzQVtU6RZ1_TgDGnk&s=2DjJqdD4A8I_dMn9gxusC4B_Vi9JphQk2P8imYs7KBY&e=
> >
> >
> > Notice that it is applied to the first 5 tiles (bi.LT.5).  Hope
> this helps.
> >
> >
> >
> >  Best regards
> >
> > Yu-Kun Qian (??????)
> > Center for Monsoon and Environment Research
> >  Department of Atmospheric Sciences
> > School of Environmental Science and Engineering
> >  Sun Yat-sen University
> > No. 135 Xingang West Road, Haizhu District
> > Guangzhou, 510275, P.R. China
> > Tel; 020-84115227
> > Email: qianyk at mail3.sysu.edu.cn      
> >
> >
> >  
> >  
> >  
> > ------------------ ???????? ------------------
> > ??????: "Ryan Abernathey"<ryan.abernathey at gmail.com>;
> > ????????: 2021??12??3??(??????) ????10:21
> > ??????: "MITgcm-support"<mitgcm-support at mitgcm.org>;
> >
> > ????: Re: [MITgcm-support] Tides in channel model
> >
> >  
> >
> > Thanks for the reply Stanislav! 
> >
> > In this case, Qiyu is working with a zonally reentrant channel (similar
> to 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__mitgcm.readthedocs.io_en_latest_examples_reentrant-5Fchannel_reentrant-5Fchannel.html&d=DwICAg&c=slrrB7dE8n7gBJbeO0g-IQ&r=5BDRdcOUIuLA0nIj7UBsNw&m=y1zd1j4BNqJV66mCcYi5svvmGr5gN1TgbfQ3HsncVPj6iFSQzQVtU6RZ1_TgDGnk&s=MXz3_QUcZCQkgP_w05JV9FpDCPDmvpD7RCBnLOaitnU&e=
> ), so there is no open boundary at which to apply tidal forcing. So
> although it is a small domain, it is more similar to a global model in this
> respect.
> >
> >
> > My understanding was that the most common way to force tides in global
> models was via a specified surface pressure field in the EXF package. (E.g.
> that's how the LLC4320 simulations were forced.) But I also know there has
> been a lot of recent work in this area, so maybe there is a simpler option.
> >
> >
> > Has anyone tried specifying a body force in analytic form using a custom
> code file? Where would be the right place in the code to insert such a
> forcing?
> >
> >
> > Best,
> > Ryan
> >
> >
> > On Fri, Dec 3, 2021 at 4:18 AM Stanislav Martyanov <
> martyanov.sd at gmail.com> wrote:
> >
> > Hello Qiyu,
> > the easiest way is to generate a simple grid with constant dx (and/or
> dy) with one or several open boundaries specified in OBCS_OPTIONS.h
> (#define ALLOW_OBCS_NORTH, etc). Then, you will need to configure the open
> boundary conditions (if you specify induced tide) and external forcing (if
> you want to set geopotantial): i.e. #define OBCS_ALLOW_TIDES in
> OBCS_OPTIONS.h, and #define EXT_ALLOW_TIDES in EXT_OPTIONS.h
> >
> >
> > And, of course, you need to set the corresponding filenames with the
> tidal forcing in data.obcs (and in data.exf, if you want geopotential).
> Note that only the normal component of tidal current at the open boundaries
> is currently implemented in the model.
> >
> >
> > You also should get familiar with the OBCS package where tides can
> be specified (as open boundary conditions), and with the EXF
> package where tides can be added through geopotental.
> >
> >
> > Best,
> > Stanislav
> >
> > ????, 1 ??????. 2021 ??. ?? 21:50, Qiyu Xiao <qx344 at nyu.edu>:
> >
> > Dear MITgcm users/developers,
> >
> >
> > If I want to run a channel model with tides, what is the best way to do
> that? What functions/variables should I change or is there any package for
> this purpose?
> >
> >
> >
> > Thanks,
> > Qiyu
> >
> >
> >  _______________________________________________
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> >
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