Supersubstorms during Storms of September 7–8, 2017

Abstract

The development of two supersubstorms (i.e., very intense substorms with an amplitude of more than 2000 nT) recorded in the main phase of two consecutive strong magnetic storms with maxima at ~0100 UT (Dst ~ –150 nT) and ~1300 UT (Dst ~ –115 nT) on September 8, 2017, is analyzed. Data from the SuperMAG global magnetometers network and the Scandinavian profile of IMAGE stations are used. Analysis of spatial distribution maps of ionospheric equivalent electric currents on the Scandinavian meridian derived according to the MIRACLE model and global maps of magnetic field vectors obtained from SuperMAG observations makes it possible to obtain the spatial distribution of planetary-scale disturbances. Both supersubstorms were characterized not only by strong nighttime disturbances at auroral latitudes (~–3600 nT and ~–2600 nT) but also by the simultaneous development of daytime magnetic bays at polar latitudes with amplitudes of ~–1000 nT and ~–400 nT, respectively. We assume that the daytime polar disturbances observed simultaneously with the supersubstorms can result from the pull of the westward ionospheric current to the dayside. Our observations support the assumption that the westward electrojet during the supersubstorm develops on a global scale from the evening to the dayside.