  For the discrete model suggested by Lorenz in 1996 a one-dimensional long
wave approximation with nonlinear excitation and diffusion is derived. The
model is energy conserving but non-Hamiltonian. In a low order truncation weak
external forcing of the zonal mean flow induces avalanche-like breather
solutions which cause reversal of the mean flow by a wave-mean flow
interaction. The mechanism is an outburst-recharge process similar to
avalanches in a sand pile model.
