[MITgcm-support] Particle tracking with MITgcm (flt package)

[Ryan Abernathey]

Andrea, you are right that the MITgcm flt package is not well documented.
However, it IS very capable and is almost certainly more efficient /
scalable than offline codes, since it parallelizes along with the rest of
MITgcm.

>
> THE QUESTIONS to the MITgcm masters:
> - does anyone know if flt can actually deal with curvilinear grids and 3D
> advection (if I understand right, the answer to the latter is yes)?
>

I have used it with cartesian and sphericalpolar grids. I to NOT know if it
works correctly with llc / exch2 / etc. Maybe Jean Michel can enlighten us.

It has options for the floats to be truly 3D, isobaric, or profiling. So
yes, 3D advection works.


> - Is there any other verification available? I cannot find any data.flt
> other than the one under flt_example.
>

Not that I know of. Here is another example:

 &FLT_NML
# 1 day
 flt_int_traj = 86400.,
 flt_int_prof =  0.0,
 flt_noise    = 0.0,
 flt_selectTrajOutp = 3,
 flt_file     = 'flt_ini_pos_hex.epac.32deg.bin',
 &

It is pretty simple. A lot of the float behavior is determined in the input
file, rather than data.flt.


> - What about advection schemes? README.flt states that second-order
> Runge-Kutta is the only option, but I was wandering if that is still the
> case and whether that is important (I am only starting to scratch the
> surface of Lagrangian methods).
>

Runge-Kutta 4th order was implemented by Andreas Klocker, and this is the
default. I believe this is considered state of the art.


> - Can flt actually interface to the diagnostic and mnc packages? A grep in
> its directory returns nothing, but my understanding of the workings of the
> code is certainly limited at best.
>

No. The float output is quite primitive and is on a tile-by-tile basis.
This makes it hard to parse and aggregate the float data. To deal with
this, we have created a python package called floater which parses and
translates the float data into other more convenient storage formats:
https://github.com/rabernat/floater
There is also some basic capability for writing the float input files.
There is still lots of room for improvement here, but it should be easier
than starting from scratch. I welcome issue reports and pull requests on
this repository.


> Thank you very much,
> Andrea
>
> --
> Andrea Cimatoribus
> postdoctoral researcher
> EPFL ENAC IIE ECOL
> https://people.epfl.ch/andrea.cimatoribus
>
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>
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