  Recently, the paradigm that the dynamic magnetosphere displays sandpile-type
phenomenology has been advanced, in which energy dissipation is by means of
avalanches which do not have an intrinsic scale. This may in turn imply that
the system is in a self organised critical (SOC) state. Indicators of internal
processes are consistent with this, examples are the power law dependence of
the power spectrum of auroral indices, and in-situ magnetic field observations
in the earth's geotail.
  An apparent paradox is that, rather than power laws, substorm statistics
exhibit probability distributions with characteristic scales. Here we discuss a
simple sandpile model which yields for energy discharges due to internal
reorganization a probability distribution that is a power law, whereas
systemwide discharges (flow of "sand" out of the system) form a distinct group
whose probability distribution has a well defined mean.
  We analyse the model over a wide dynamic range whereupon two regimes having
different inverse power law statistics emerge, corresponding to
reconfigurations over two distinct scaling regions: short scale sizes sensitive
to the discrete nature of the sandpile model, and long scale sized up to the
system size which correspond to the continuous limit of the model. The latter
are anticipated to correspond to large scale systems such as the magnetosphere.
  Since the energy inflow may be highly variable, we examined the response of
the model under strong or variable loading and established that the power law
signature of the large scale internal events persists. The interval
distribution of these events is also discussed.
