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

[Ryan Abernathey]

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> 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/
> (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/
> 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
> 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                   |
> |   Jeff Blundell,  Room 256/09  |  OES Physical Oceanography Group, |
> |    phone: +44 [0]23 8059 6201  |  National Oceanography Centre,    |
> |     fax : +44 [0]23 8059 6204  |  Southampton, European Way,       |
> |                                |  SOUTHAMPTON SO14 3ZH, UK.        |
> |      WWW: http://www.southampton.ac.uk/oes/about/index.page?       |
> ======================================================================
>
> ________________________________________
> From: Andrea Cimatoribus [andrea.cimatoribus at epfl.ch]
> Sent: 22 February 2017 13:49
> To: 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).
>
> 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
>
>
>
> 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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