Periodical occurrence of the disruptions along the Earth's magnetic tail and cross-tail current amplifications

The field-aligned currents (FACs) flow to the ionosphere from the edges of the inhomogeneities of the perpendicular magnetospheric current (PMC) which is the source of these FACs. One such PMC is the dawn-dusk cross-tail current in the substorm current wedge (SCW) with pair of FACs in the night sector of the Iijima-Potemra Region 1 (thereinafter R1). This FACs pair is created by disruption of the above PMC. Another such PMC is the dawn-dusk partial ring current (DRP) with pair of FACs of Iijima-Potemra R2. This pair of FACs is created by amplification of the PMC/DRP. These two pair FACs are well-known. In the present study were detected also other five FACs pairs of SCW or DRP types, the chain of seven pairs in total. The maps of the FAC density spatial distribution in the polar ionosphere for three selected substorm were used. The chain of the seven FACs pairs was found to be placed approximately along the midday-midnight meridian. When the sign plus (minus) is accepted for SCW (DRP) types, then in this chain each positive pair follows a negative pair periodically. Assuming the distance between neighboring pairs is a half of the wave length, λ/2, and given from observations the temporal period T, the velocity V= λ/T was determined, and its different values in different domains of the magnetosphere were found to be all compatible with the expected values for V of the magnetosonic waves. The above results were obtained for the first time. The ground-based magnetometers data and the original magnetogram inversion technique, MIT-2, were used. Analogs of our conclusions are absent in the published statistical models of FACs based on the satellite measurements. It is likely that a satellite makes only local measurements, and variable spatial features and important details are smoothed at an averaging of the satellite measurements.