A model of spatio-temporal structure of the substorm electromagnetic disturbance and its consequences

Abstract

In the outer quasi-dipole zone of the magnetosphere, transverse-small-scale standing Alfven waves form resonant response in that zone to the nonresonant disturbances penetrating there from the geomagnetic tail during substorm activations. A shortlived source acting in a relatively narrow L interval is assumed. It is located in the nightside sector, in the vicinity of the boundary between tail-like and dipole-like field lines. The resonant waves are Alfven field-line oscillations with a continuous frequency spectrum. During their radial propagation between the poloidal and toroidal resonant surfaces, different spectral components phase mix; this produces a fast decrease of the resulting disturbance amplitude. The original theory by Leonovich and Mazur is generalized to take into account these effects due to a nonmonochromatic and nonuniform features of the source disturbance. Analytical approach provides asymptotic estimates of the resonant response time scale as dependent on those source features.The theory is aimed at elaboration of an adequate three-dimensional spatio-temporal model of intense electromagnetic disturbances in the nightside magnetosphere which are associated with substorm activations and are observed as time-dependent substorm current wedges and Pi2 pulsations.Another application of the theory is connected with intense short-term induction electric field due to the resonant disturbance. This should act as a mechanism of acceleration for energetic particles.