1999/11/18 by S. C. Chapman, Chapman, S. C., N. W. Watkins +3
Biochemistry, Genetics and Molecular Biology · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics (astro-ph) #Earthquake Detection and Analysis #FOS: Physical sciences #Geology and Paleoclimatology Research #Geomagnetism and Paleomagnetism Studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/9911356
1 latex file, 10 postscript figures using psfig. Submitted to JASTP
arxiv created 1999/11/18 · openalex publication_date 1999/11/18 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
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.