Avalanching Systems and SOC in Space: Models and Observations

The concept of self-organized criticality, which was introduced on the basis of sandpile models, quickly found its way into space physics and astrophysics. By now a number of systems in space were suggested to possess avalanching behavior and SOC features. Virtually all of them are related to the dynamics of magnetic fields, in particular, to the reconnection process. Remote observations in space, like measurements of aurora produced due to the reconnection in the current sheet, may be more informative than laboratory experiments, since they allow to get information from inside the system and not only on the energy release at the boundaries. Proper interpretation of these remote measurements should take into account possible influence of the medium between the avalanching system itself and the observation site. Application of proposed SOC models to the observed physical phenomena requires proper identification of real avalanching processes. We demonstrate, on the basis of the recently proposed burning model, what modes of measurements are mostly reliable for comparison of observations with avalanching models. In particular, we propose a cluster analysis as a powerful tool. We also show that dimensionality of the avalanching system should be taken into account for comparison of models with observations, since the observed statistical behavior may significantly change with the change of dimensions, even when the underlying physical mechanism remains the same.