Statistical Studies of Auroral Activity and Perturbations of the Geomagnetic Field at Middle Latitudes R.

Abstract

In this paper, we statistically analyzed substorm activity at auroral latitudes for 2007–2020 and itsrelationship with magnetic disturbances at middle latitudes using the INTERMAGNET, SuperMAG, andIMAGE magnetometer data. The appearance and development of magnetic disturbances at auroral latitudeswas monitored by the IL index (similar to the AL index, but calculated according to IMAGE data). For the2007–2020 period, events that were observed near the meridian of the IMAGE network, in the night sector(2103 MLT), were selected. Two samples of events were used: (1) IL –200 nT for at least 10 min, with anadditional criterion for the presence or absence of positive bays at the Panagyurishte station in Bulgaria, and(2) isolated substorms observed on the IMAGE meridian according to the list of Ohtani and Gjerloev (2020).The distributions of the IL index, as well as the empirical and theoretical cumulative distribution functions,are obtained, and the of the occurrence of extreme events are also estimated. It is shown that, in general, theIL distributions are described well by exponential functions, and out of all events, events accompanied bymid-latitude positive bays were observed in ~65% of cases while their fraction increased with increasing disturbanceintensity. Events with positive bays at midlatitudes of MPB and isolated substorms were betterdescribed by the Weibull distribution for extreme events. From both distributions, annual and semi-annualvariations were identified: annual variations have a summer minimum and a winter maximum, and semiannualvariations have maxima near the equinoxes, which is most likely due to the Russell-McPherron effect.The semi-annual variation is also shown to be more pronounced for events with accompanying mid-latitudinalpositive bays.