Running Veros

Veros is a general ocean circulation model (GCM) that is written in python. That makes it a bit slower than models written in C or FORTRAN, but we can learn a lot with relatively coarse simple simulations, using the model as a numerical laboratory to see the basic physics governing the ocean.

Despite our basic usage, Veros is pretty full-featured. It has forcing from both wind stress and buoyancy forcing, and it has a relatively full-featured set of turbulence closure schemes to represent un-resolved turbulence.

Installation

Veros should have been installed as part of your eos431 environment (see Setting up a python environment). After doing mamba activate eos431 you should be able to use the veros command line tool:

veros --help

should echo to the command prompt:

Usage: veros [OPTIONS] COMMAND [ARGS]...

  Veros command-line tools

The setup file

Each model run can be setup from a single python file that is called from the veros command-line tool, eg:

veros run --force-overwrite example.py

Where here we have named the setup file example.py. Depending on what information is in this file, the program will run, sometimes for quite a while, and create netcdf files of the output. For instance, this file might create a netcdf file named example.snapshot.nc.

For your assignments, I have already created these files for you. However, you may wish to consult them to see how the models are set up.

Most of you should have mpi installed with eos431 environment as well. If you do, this can be used to speed up veros runs by using multiple processors on your machines. You of course shouldn’t use more processes than you have cores in your computer, and it actually can be counter-productive to use too many cores. But some of the processes here can be sped up using 4 cores. For instance, if we wanted to divide the x-y domain into 4 subdomains in x and 1 subdomain in y, we can do:

mpirun -np 4 veros run --force-overwrite example.py -n 4 1

A good rule of thumb is that its not worthwhile making either x or y less than 40 tiles wide. So example.py, we have settings.nx = 200, so this is worth dividing into 4 cores, whereas settings.ny = 4 is definitely not worth dividing.

Output files

As noted, veros will output example.snapshot.nc. It may also make *.h5 restart files, which can be used to restart the model from part way through a run.