Fig. 12From: Auroral substorms as an electrical discharge phenomenon(Left) The figure shows how the magnetosphere is inflated and deflated; the magnetic energy in this case is 2.9 × 1021 ergs (almost one tenth of the substorm energy) and β ∼ 1.0 at a distance of 6 Re. The expansion phase occurs when the magnetosphere unloads the accumulated energy and becomes deflated. (Right) When a moderately high S–M power ε is maintained almost constantly for more than 10 h, substorms occur repeatedly and successively, suggesting that the magnetosphere can accumulate only a limited amount of magnetic energy (at most, 1023 ergs) and become unstable and thus unloading repeatedly the accumulated magnetic energyBack to article page