## Simple Barotropic Model

Three mathematicians named Courant, Friedrichs, and Lewy created a
criterion that, if violated, would lead to the "blowing up" of a
finite-difference weather prediction model. This **CFL** criterion
is:

`
The speed of fastest winds in model must be less than or equal to
grid spacing divided by the time step.
`
Because of the CFL criterion, a modeler cannot arbitrarily choose a
horizontal grid spacing without also taking into account the time step of the
model.
If you want fine horizontal resolution to see small-scale weather, you must
have fine time resolution too. Otherwise, the model "blows up"

What does it look like when a model "blows up"? Try it yourself using the below
applet. Troughs and ridges turn disintegrate when the horizontal grid spacing and time step don't satisfy the CFL criterion. The forecast is ruined. (See
the detailed instructions, below.)

Instructions

- Set parameters
- Click Run
- After 48 hours, it will stop; you can click Run again to
continue or Reset to change parameters and re-start
- You may also hit Reset any time to change parameters and re-start
- Enjoy!

This webapp is Copyright © 2015 by Tom Whittaker.