Characteristic features of latitudinal manifestations of the 23–24 April 2023 geomagnetic storm

Abstract. The paper examines, for the first time, the latitudinal dependence of variations in the geomagnetic field on the surface of the Earth on the global scale during the severe two-step geomagnetic storm of 23–24 April 2023, a major two-step storm in solar cycle 25. The data available at INTERMAGNET magnetometer network URL (https: //imag-data. bgs. ac. uk/GINV1/GINForms2) were chosen for two near-meridional chains of stations, one in the western (eight stations) and the other in the eastern (ten stations) hemispheres, which were situated, for the first time, in such a way that one of them was in the night hemisphere during both of the two steps of the geomagnetic storm. One of the most interesting observations made show that during one step of the two-step storm part of the near-Earth cross-tail current closed itself via the ionosphere, to which it was linked by the substorm current wedge, and manifested itself in the magnetograms acquired at high and equatorial latitude stations on the night side of the Earth. The two-step character of this storm has allowed us to suggest that the Bz interplanetary magnetic field component threshold for the formation of the substorm current wedge lies in the – (22–30) nT interval. Other features of this two-step storm include the following. In the western hemisphere, the fluctuations of the geomagnetic field strength on the days used as a quiet time reference period usually did not exceed a few tens of nanotesla (nT), whereas in the course of the disturbed days, the variations in the geomagnetic field strength increased by a factor of 2 to 10 and reached a few hundred nT. In the eastern hemisphere during quiet times, the middle and low latitude magnetometer stations generally recorded strength fluctuations smaller than 10–20 nT, while during the disturbed period the fluctuations increased by a factor of 2–5 and greater, attaining ± (50–70) nT. The strength fluctuations showed a considerable, up to 300–700 nT, increase at high latitudes. The northward component of the geomagnetic field, X, exhibited the greatest perturbations at all latitudes in both hemispheres, as the level of strength fluctuations decreased with decreasing latitude. The geomagnetic field strength fluctuations recorded at the magnetometer stations nearly-equidistant from the equator were observed to be close in magnitude. Close in value also were the strength fluctuations observed with the stations at close latitudes but in different hemispheres.