Why errors are growing beyond courant number limit?

[eswarm21]

why errors are growing beyond courant number limit? i know that it depends on the scheme which we applied to the problems. But why it is ? which property leads it to stable or unstable region during Fourier analysis?

 

[Aero_UoP]

To see if the scheme you use is stable you have to perform a von Neumann analysis:
http://en.wikipedia.org/wiki/Von_Neumann_stability_analysis