Features of Longitudinal Variations of Geomagnetic and Ionospheric Parameters during Severe Magnetic Storms in 2015

The paper was carried out as a part of the project devoted to a comprehensive study of the longitudinal variations of the Earth's magnetic field in middle and high latitudes of the Northern hemisphere and related variations in the midlatitude ionosphere in disturbed and quiet geomagnetic conditions in 2011-2017. The analyzed period covers the years of growth, maximum and decline of the 24th cycle of solar activity. To study the geomagnetic field variations, data from the INTERMAGNET global network of magnetometers in the Northern hemisphere were used. In the analyzed time period 122 events of magnetic storms were identified: 102 moderate , 18 strong and 2 severe . A statistical analysis of the distribution of magnetic storms by years and seasons was performed. New interesting results are obtained on the irregular structure of the longitudinal variability of the geomagnetic field components in quiet conditions due to the discrepancy between the Northern geographical and geomagnetic poles, as well as the presence of anomalies of different spatial scales in the background magnetic field of the Earth. The longitudinal-temporal variations of the geomagnetic field components under disturbed conditions also show a strong dependence on the individual features of the magnetic storms. On the case study of the development of two severe magnetic storms in 2015, the longitudinal-temporal variations of the parameters of the midlatitude ionosphere over the Eurasian continent were analyzed based on the analysis of the ionosonde chain data. The presence of longitudinal features of the background structure and variations of the geomagnetic field leads to the fact that the registered ionospheric effects also exhibit a significant longitudinal inhomogeneity. We assume that the storm-associated ionosphere dynamics is determined by the lower thermosphere disturbances due to the auroral electrojet amplifications producing the enhanced neutral wind and turbulences; these, in turn, uplift the molecular gas to the ionospheric heights. This process decreases the [O]/[N
₂
] ratio and, consequently, the electron density.