The analogy between the dynamic magnetosphere and an avalanche system is examined by using the global auroral energy deposition obtained by the Polar UVI as a measure of the energy output of the magnetosphere. The analysis reveals two types of energy dissipation: those internal to the magnetosphere occurring at all activity levels with no intrinsic scale, and those associated with active times corresponding to global energy dissipation with a characteristic scale. The internal events exhibit the same power law index in both active and quiet times. These features are consistent with a simple avalanche ('sandpile') numerical model. ¿ 2000 American Geophysical Union