Substorm related patterns of electron density and conductance changes in the auroral zone.

Abstract

<p>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. We use linear prediction filter technique to reconstruct the substorm-related response of electron densities at different altitudes and ionospheric conductances from long-term observations made by the European Incoherent SCATer (EISCAT) radar located at Tromso. 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. The duration of the response is about 3 hours. 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. Model performance is better at the midnight-morning sectors (CC~0.6-0.65), where the response is larger, and it is getting worse at the noon-evening sector (CC~0.3-0.5). We also discuss the changes of effective electron energy spectra with the substorm time and MLT and compare the behaviors of global ionization, auroral absorption and conductance patterns as it propagates azimuthally from midnight along the auroral zone following after T0 time. Research was supported by RFBR grants №19-35-90054 and №19-05-00072 and MON grant №2020-220-08-6949.</p>