A 2-layer forced quasi-geostrophic channel model

This model simulates a simple 2-layer system governed by quasi-geostrophic physics by solving two prognostic equations: 1) tendency of the mean background potential vorticity gradient "dq_bar/dy" and 2) tendency of the anomalous "eddy" potential vorticity "q". The current make.sh and Makefile compile the source code for the University of Chicago's "Midway" supercomputer.

Usage

In a nutshell, to run the model, call run.sh expname [param1=value1] [param2=value2] (or write an sbatch script that calls it). The experiment name is the name of the directory in scratch where output will be saved (the directory will be created if it does not exist). If you call run.sh with just an experiment name, run.sh will look for the namelist modifications associated with that experiment in the file experiments.txt. If you call run.sh with any param=value pairs, the those assignments will be added to the namelist instead. Check out the source code for run.sh for more information. The run script also calls make, to compile any modificiations to the source code.

Forcing

The model is forced in five ways:

1. "Radiation": Relaxation of the upper and lower-layer winds toward an "equilibrium", spatially uniform shear (the value "shear" provided in the namelist).
2. "Friction": Relaxation of the lower-layer relative vorticity toward zero.
3. "Diffusion": Damping of potential vorticity proportional to its n'th spatial derivative; defaults to the 6th derivative.
4. Sponge: Relaxation of the lower and upper-layer relative vorticity toward zero, in the exact same way as friction, near the top/bottom "edges" of the channel.
5. PV Injection: Application of PV tendency anomalies in narrow spectral band, localized to center of channel and with e-folding timescale of the autocorrelation specified by an "injection timescale".

Namelist

The model can read a namelist file to tune the model timing, background state, and forcing schemes. See the default namelist file input.nml and the global variables file global_variables.f90 for details. Here are a few explanations:

• y_sp controls the proportion of each top/bottom "half" of the channel covered by sponge damping.
• y_i controls the width of the pv injection region, same units as above; pv injections are weighted in y by the simple Gaussian curve exp(-(y-0.5*width)^2/(y_i)^2).
• tau_r, tau_f, tau_sp are the timescales for radiation, friction, and sponge damping in days, respectively.
• contin_i toggles between a continuous, autocorrelated pv injection, and a discrete pv injection every tau_i days.
• tau_i when contin_i is true is the e-folding time, in days, for the autocorrelation function underlying the pv injections; when contin_i is false, it is the discrete injection interval (i.e. we inject pv every tau_i days).
• wmin_i and wmax_i are the minimum and maximum integer wavenumbers for the pv injections.
• amp_i is the maximum amplitude of the pv injections, in units 1/s^2 (remember we inject pv tendencies).
• shear and beta control the background state.
• rd is the Rossby radius of deformation; it is a function of beta, gravity, and layer height.