[MITgcm-support] from C- to A-grid (particle tracking)

Wed Feb 22 11:02:03 EST 2017

Thanks for all the feedback, I have to study the material and may get 
back to (some of) you later.
Cheers,

Andrea Cimatoribus
postdoctoral researcher
EPFL ENAC IIE ECOL
https://people.epfl.ch/andrea.cimatoribus

On 22/02/17 15:34, Ryan Abernathey wrote:
> Andrea,
>
> Moving from an A grid to a C grid does require interpolation. If you are
> doing Lagrangian particles, the induced divergence might not be a
> problem, since a slightly non-divergent velocity field won't cause any
> serious problems. So a naive multilinear interpolation may be fine.
>
> If you need to advect tracers offline, you need a velocity field that is
> exactly non divergent and satisfies the boundary condition at the side
> walls. This can be obtained by decomposing the velocity into
> streamfunction and velocity potential components, which requires solving
> an elliptic Poisson PDE. The MITgcm can be hacked to solve this for you.
>
> We have done exactly what you describe in the following papers, where we
> use AVISO geostrophic velocities (on an A-grid) to advect tracers and
> particles within MITgcm.
> http://doi.org/10.1002/jgrc.20066
> http://doi.org/10.1175/JPO-D-13-0159.1
> http://doi.org/10.1175/JPO-D-16-0215.1
>
> If you like, I can provide you more details.
>
> Cheers,
> Ryan
>
>
> On Wed, Feb 22, 2017 at 9:20 AM, Blundell J.R. <jeff at noc.soton.ac.uk
> <mailto:jeff at noc.soton.ac.uk>> wrote:
>
>     Hi Andrea,
>               This isn't a simple answer to your question, but you might
>     like to have a look at ARIANE:
>     http://stockage.univ-brest.fr/~grima/Ariane/
>     <http://stockage.univ-brest.fr/~grima/Ariane/>
>     (original webpage)
>     which is heavily used here at NOC, Southampton. It has native support
>     for some curvilinear C-grid models, such as OPA-NEMO and ROMS,
>     though not (as far as I can see) MITgcm. Given that it has support for
>     several models, I would imagine that the logic of adding another might
>     not be too bad, perhaps easier that interpolating onto a regular A-grid.
>     We use v2.2.8_05 .
>     See also
>     http://salishsea-meopar-docs.readthedocs.org/en/latest/particles/
>     <http://salishsea-meopar-docs.readthedocs.org/en/latest/particles/>
>     which seems to have some of the most up-to-date documentation.
>     I should explain that I build the software (that part works quite well)
>     for others to use; I'm not a user myself.
>     http://earthscience.stackexchange.com/questions/761/what-are-some-
>     options-for-online-and-offline-particle-tracking-in-ocean-models
>     <http://earthscience.stackexchange.com/questions/761/what-are-some-
>     options-for-online-and-offline-particle-tracking-in-ocean-models>
>     seems to suggest that CMS can handle "various Arakawa-staggered grids",
>     as presumably it must if it handles HYCOM and ROMS output.
>
>                                 Jeff Blundell
>     ======================================================================
>     |              Research Fellow in Physical Oceanography              |
>     |                    e-mail:  jeff at noc.soton.ac.uk
>     <mailto:jeff at noc.soton.ac.uk>                   |
>     |   Jeff Blundell,  Room 256/09  |  OES Physical Oceanography Group, |
>     |    phone: +44 [0]23 8059 6201
>     <tel:%2B44%20%5B0%5D23%208059%206201>  |  National Oceanography
>     Centre,    |
>     |     fax : +44 [0]23 8059 6204
>     <tel:%2B44%20%5B0%5D23%208059%206204>  |  Southampton, European
>     Way,       |
>     |                                |  SOUTHAMPTON SO14 3ZH, UK.        |
>     |      WWW: http://www.southampton.ac.uk/oes/about/index.page
>     <http://www.southampton.ac.uk/oes/about/index.page>?       |
>     ======================================================================
>
>     ________________________________________
>     From: Andrea Cimatoribus [andrea.cimatoribus at epfl.ch
>     <mailto:andrea.cimatoribus at epfl.ch>]
>     Sent: 22 February 2017 13:49
>     To: mitgcm-support at mitgcm.org <mailto:mitgcm-support at mitgcm.org>
>     Subject: [MITgcm-support] from C- to A-grid (particle tracking)
>
>     Dear all,
>     I am in the process of setting up some particle tracking experiments.
>     After some research and some thinking about my needs, I am inclined to
>     use an offline tool rather than the MITgcm flt package, most likely CMS
>     (https://www.rsmas.miami.edu/users/cparis/oss.html
>     <https://www.rsmas.miami.edu/users/cparis/oss.html>).
>
>     In order to use CMS, I need to interpolate the MITgcm results from my
>     native curvilinear C-grid to the non curvilinear, non rotated A-grid
>     which CMS requires. My questions then are:
>     - is there a way to do this interpolation maintaining the flow (at least
>     approximately) non divergent? (with complex boundaries)
>     - does anyone have any suggestion on working with MITgcm+CMS, or more in
>     general with MITgcm+particle tracking?
>
>     The alternative is to implement C-grids in CMS, which would be
>     interesting but I'm not yet sure it's realistic.
>
>     Thanks, Andrea
>
>
>     --
>     Andrea Cimatoribus
>     postdoctoral researcher
>     EPFL ENAC IIE ECOL
>     https://people.epfl.ch/andrea.cimatoribus
>     <https://people.epfl.ch/andrea.cimatoribus>
>
>
>
>     PS: To answer the obvious question one may have: I think that the flt
>     package is not the right tool for me, since I would like to have several
>     particles (>>1000), doing repeated experiments over the same period of
>     time, in a rather small domain. I think that an offline tool is in this
>     case not only much faster, but also much more flexible.
>
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