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Abstract. Intermittency is one of the possible means of quantifying dynamics of fractal processes. In this paper, the analysis of the intermittency of magnetospheric storms and substorms is presented. The analysis allows for a classification of the processes in terms of the power-law scaling of the magnitude of deviations of the index values from the values at quiet times (normal state), and the relative timings of occurrences of such deviations. These are expressed in terms of the co-dimension and the Fano factor. The relationship between the two is related to the nature of the processes behind the observed storm and substorm dynamics. The results suggest that there is a similarity between the two, and therefore it is possible that there are common dynamical processes behind the storms and substorms. In particular, it appears that both of them behave consistently with what would be expected for critical systems, which is consistent with the conclusions of several previous works.

Using a stability analysis based on a Lagrangian–Hamiltonian approach to magnetohydrodynamics, this paper addresses the stability of the Earth’s magnetotail during the later stages of the growth phase of the substorm. The analysis shows that the magnetotail at about 10–12RE is the likely region for instability. Furthermore, the analysis helps to explain why the substorm intensification begins on field line mapping from the Earthward edge of the substorm plasma sheet to auroral arcs near the equatorward edge of the auroral region. Our model and analysis provides a possible explanation for pseudobreakups as well as the initiation of more global substorm intensifications. A stability analysis of the evolving stretched field configurations of the growth phase shows that initially, at a certain level of stretching and in regions where the plasma β is 5–10, localized instabilities are possible. These localized instabilities saturate before producing a more global instability and the reconfiguration of the magnetic field topology of the magnetotail. Eventually the threshold for nonlinear instabilities is reached and a global, explosive instability is possible. Even though this paper looks only at the possibility of explosive instabilities and the initial stages of the substorm intensification, it provides an important first step in forming a complete picture of the substorm instabity and the subsequent return to a lower energy, metastable state through dipolarization of field lines in the magnetotail. A number of important features in the initiation of the substorm intensification can be explained by considering an explosive ballooning mode. Nevertheless, a more complete analysis of the plasma dynamics associated with the instability initiating the substorm intensification and the subsequent evolution of the substorm, including kinetic effects and reconnection, is needed for a more complete model of the substorm process.

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It has been previously demonstrated that several minutes prior to an onset of a magnetospheric substorm the near-Earth plasma sheet becomes unstable to resonance-type perturbations. The next logical step, examined here, is an assumption that the velocity shear in the resonance would lead to a development of a Kelvin–Helmholtz (KH) instability. Using a Grad-Shafranov equilibrium constrained by CANOPUS data, we analyze the stability properties of the near-Earth plasma sheet in the presence of a field-line resonance-generated KH instability at around 10 Earth radii. The results of the analysis are in general agreement with observations and computer modeling of substorms. As a part of the analysis, we discuss the importance of the proper distinction between the stability properties of the magnetotail, and the trigger mechanism responsible for the instability. While these two aspects of a substorm may be (and likely are) related, it is possible that they involve different types of processes that work in a complementary fashion. PACS Nos.: 06.54, 27.40, 27.72, 27.88