The generator system of field-aligned currents during the April 06, 2000, superstorm

Abstract

Using ground-based magnetometer data of the April 6–7, 2000, superstorm, we obtained maps of ionospheric and field-aligned currents (FACs). Based on these, we deduced the electrical circuit of the disturbed magnetosphere/ionosphere and a conceptual model of its magnetospheric generators, which supply both hemispheres. This model implies that the generator system creates primarily the Region-1 FACs of Iijima and Potemra at both hemispheres, while the Region-2 and Region-0 FACs form by spreading of the Region-1 currents through the ionosphere. This conclusion is supported by observations. A second prediction of this model turns out to be the following hypothesis, which is also based on the new empirical data. The Region-2 FAC of the dawn side in the Northern Hemisphere is connected with the global dynamo via the asymmetric ring current of the inner magnetosphere, DRP-1. Coming with the DRP-1 into the dusk side, the Region-2 FAC then splits and connects with the dusk side ionosphere of both hemispheres. This way a part of the dawn side Region-1 current becomes connected with the dusk side dynamo of the opposite hemisphere. The intensity of Region-2 and Region-1 FACs of the dusk side is therefore smaller than on the dawn side of this hemisphere, provided that the conductivity in the magnetically conjugated Region-2 ionosphere is larger than the local. Similarly, the dawn–dusk asymmetry of the FAC intensities may also be caused by an inequality of magnetic field and/or pressure gradient in the northern and southern halves of the plasma sheet where DRP-1 flows. The predicted dawn–dusk asymmetry according to such a model is supported by the observations and appears causally connected with an asymmetry between the hemispheres. This conclusion opens a new approach to study these kinds of FAC asymmetries. Further analysis led to the additional conclusion, that the global magnetospheric dynamo works as a voltage generator both during relatively quiet (average) conditions as well as under strong disturbance conditions.