Spectral statistics of global avalanches along granular piles

In a seminal experiment, Jaeger et al. (Phys. Rev. Lett., 62 (1989) 40) measured the power spectrum of the velocity of avalanches along a granular pile in a rotating drum. Although their findings started an actively discussed debate on whether self-organized criticality rules granular avalanche dynamics, their experimental results have not been explained in theoretical detail yet. By the use of a simple dynamical model that incorporates the basic deterministic mechanisms of global avalanche flow as well as their stochastic aspects, we find almost perfect agreement between the model results and Jaeger et al.'s experimental data. We also discuss in detail the significance of the underlying physical mechanisms.