We have developed a new procedure for combining lists of substorm onset times from multiple sources. We apply this procedure to observational data and to magnetohydrodynamic (MHD) model output from 1-31 January, 2005. We show that this procedure is capable of rejecting false positive identifications and filling data gaps that appear in individual lists. The resulting combined onset lists produce a waiting time distribution that is comparable to previously published results, and superposed epoch analyses of the solar wind driving conditions and magnetospheric response during the resulting onset times are also comparable to previous results. Comparison of the substorm onset list from the MHD model to that obtained from observational data reveals that the MHD model reproduces many of the characteristic features of the observed substorms, in terms of solar wind driving, magnetospheric response, and waiting time distribution. Heidke skill scores show that the MHD model has statistically significant skill in predicting substorm onset times.

Enhanced precipitation of magnetospheric energetic particles during substorms increases ionospheric electron density and conductance. Such enhancements, which have timescales of a few hours, are not reproduced by the current ionospheric models. Using EISCAT (Tromso) measurements we reconstruct the substorm related response of electron densities and conductances in the ionosphere with respect to the intensity of substorm injections. We also investigate how the intensity of the response is influenced by the variations of the plasma sheet high energy (tens keV) fluxes and solar wind state. To characterise the intensity of substorm injection at a 5min time step we use the midlatitude positive bay (MPB) index which basically responds to the substorm current wedge variations. We build response functions (LPF filters) between T0-1h and T0+4hrs (T0 is a substorm onset time) in different MLT sectors to estimate the magnitude and delays of the ionospheric density response at different altitudes. The systematic and largest relative substorm related changes are mostly observed in the lowest part of E and in D regions. It starts and reaches maximum magnitude near midnight, from which it mainly propagates toward east, where it decays when passing into the noon-evening sector. Such MLT structure corresponds to the drift motion of the injected high energy electron cloud in the magnetosphere. Besides the injection intensity, we look at how the magnitude of the response depends on the energetic (tens keV) fluxes level in the plasma sheet before the substorm onset. We use a previously developed empirical model of the plasma sheet fluxes with solar wind parameters as inputs to count the plasma sheet fluxes with energy 10, 31 and 93 keV in the reference point of transition region (6 Re, 270o SM Long). We found that during enhanced high energy fluxes in the plasma sheet before the substorm (fast solar wind, high solar wind reconnection electric field) the background ionisation in the ionosphere, as well as the peak ionisation value during the substorm, are higher. This implies that together with substorm intensity the prehistory of the plasma sheet/solar wind state forms the magnitude development of substorm related ionospheric response. Research was supported by Russian Ministry of Science and Higher Education grant № 075-15-2021-583

The substorm current wedge (SCW) is believed to be driven by pressure gradients and vortices associated with fast flows. Therefore, it is expected that relevant observations are organized by the SCW’s central meridian, which cannot be determined using in-situ observations. This study takes advantage of the SCW inversion technique, which provides essential information about an SCW (e.g., location and strengths of field-aligned currents (FACs) and investigates the generation mechanisms of the SCW. First, we have found good temporal and spatial correlations between earthward flows and substorm onsets identified using the midlatitude positive bay (MPB) index. Over half of the flows are observed within 10 minutes of substorm onsets. Most flows (85%) were located inside the SCW between its upward and downward FACs. Second, superposed epoch analysis (SPEA) shows that the onset-associated flow velocity has a flow-scale (3-min) peak, while the equatorial thermal pressure has a substorm-scale (>30 min) enhancement and a trend similar to the westward electrojet and FACs in the SCW. Third, the pressure gradient calculated using in-situ observations is well organized in the SCW frame and points toward the SCW’s central meridian. These facts suggest that the SCW is likely sustained by substorm-scale pressure gradient rather than flow-scale flow vortices. The nonalignment between the pressure gradient and flux tube volume could generate an SCW with a quadrupole FAC pattern, similar to that seen in global MHD and RCM-E simulations. Their magnetic effects on the ground and geosynchronous orbit resemble a classic one-loop SCW.