This study, for the first time, convincingly attests to the two-step geospace storm being the best possible solar–terrestrial event of opportunity for realizing a technique for estimating the interplanetary magnetic field (IMF) B_z component threshold for the formation of the substorm current wedge. The data from INTERMAGNET magnetometer network on the two-step geospace 23–24 April 2023 storm yield the IMF B_z threshold for the formation of the substorm current wedge of –(22–30) nT.

Substorms are a phenomenon in the magnetosphere–ionosphere system, which are characterised by brightening of an auroral arc and enhancement of electric currents in the polar ionosphere. Since substorms are difficult to predict, this study treats a substorm occurrence as a stochastic phenomenon and represents the substorm occurrence rate with a machine learning model. We then analyse the response of substorm activity to solar wind conditions by feeding synthetic solar wind data into the model.

The relationships between auroral activity and the solar-wind conditions are modeled with a machine-learning technique. The impact of various solar-wind parameters on the auroral activity is then evaluated by putting artificial inputs into the trained machine-learning model. One of the notable findings is that the solar-wind density effect on the auroral activity is emphasized under high solar-wind speed and weak solar-wind magnetic field.

We used up-to-date substorms, HILDCAAs and geomagnetic storms of varying intensity along with all available geomagnetic indices during the space exploration era to explore the seasonal features of the geomagnetic activity and their drivers. As substorms, HILDCAAs and magnetic storms of varying intensity have varying solar/interplanetary drivers, such a study is important for acomplete understanding of the seasonal features of the geomagnetic response to the solar/interplanetary events.

Comprehensive analysis of a moderate substorm was performed using optical observations inside the auroral oval and in the polar cap, combined with data from satellites, radars, and ground magnetometers. The onset took place near the poleward boundary of the auroral oval that is not typical for classical substorms. The data fit to the near-tail current disruption scenario of the substorm onset. The role of the 15 min oscillations in the IMF Bz component in the substorm initiation is discussed.