Robustness of collective behaviour in strongly driven avalanche models: magnetospheric implications

The hypothesis of self-organised criticality (SOC) predicts that certain op en dissipative systems evolve to a critical state where all energy release statistics display power law distributions for event occurrence, size and d uration. This has motivated "sandpile" simulations of magnetospheric energy confinement and release events ("avalanches") I previous examples of which have taken the limit where energy inflow ("fuelling") is slow relative to dissipation, and either uniform or random. However the magnetospheric syste m has both slow and fast periods mixed together in observations, and natura lly modulated fuelling. We have developed an avalanche model with variable, modulated fuelling rate. The power law form for the distribution of energy release events is the least ambiguous current indicator of SOC; we show th at this is preserved for the large avalanches in such a system under both c onstant and varying loading and so such systems are remarkably efficient at eliminating small scale information about their fuelling.