Geomagnetic Disturbances and Midlatitude Airglow During the 20 December 2015 Magnetospheric Storm

Abstract

We report on the novel features of stormtime, midlatitude PiB/PiC geomagnetic pulsations, ionospheric and field-aligned currents, and oxygen, O¹S and O¹D, emissions at 557.7 and 630.0 nm, respectively. Those were observed during the main phase of the 20 December 2015 storm with significant variations of the solar wind dynamic pressure, P_d, and interplanetary magnetic field B_z. Intensifications of the shortest period, Т < 10 s, Pi1B pulsations and oxygen emissions marked the substorm onsets. The distinct characteristic of the strong substorm (SME = 2,910 nT) was the presence of bay-like geomagnetic variations with the X and Z components with the opposite signs in the northern and southern sections of the IMAGE chain near 18 MLT. Using the magnetogram inversion technique of our institute, we obtained the MLT-MLAT distribution (map) of equivalent and field aligned currents revealing an additional westward electrojet to the north of the eastward current. We have shown that such a current system provides the observed distribution of geomagnetic variations along the 18 MLT meridian during the 20 December 2015 strong substorm, including at the high-latitude half of the IMAGE chain of stations. These conclusions were clearly validated by our simple current system model. We also revealed a localized geomagnetic event during the SME decrease interval between two substorm activations, when the magnitudes of the H/X geomagnetic component, PiB/PiC pulsations, and oxygen emissions at mid latitudes were more than twice greater than during the strong substorm.