## 3 Results  
Geomagnetic storms are initiated by the arrival of geo-effective solar wind flows at the Earth's vicinity (see, for instance [6; 7; 8; 9; 10; 11; 12; 13; 14; 15]). Geo-effectiveness is determined by a combination of solar wind velocity and southward orientation of the Interplanetary Magnetic Field (IMF), with the second to hold the most important role because of its far greater variability. Magnetic reconnection is the key physical process responsible for transferring solar wind energy into the magnetosphere during geomagnetic storms, being strongest under southward IMF orientation: southward directed IMF interconnects with the Earth's magnetopause northward magnetic field and solar wind drags the interconnected magnetic fields and plasma downstream (i.e., in the antisunward direction); the open magnetic fields then reconnect in the magnetotail. The relative rate of the reconnection in the magnetopause and magnetotail sets off a global convection cycle of magnetic flux between the dayside and nightside magnetosphere. The convection cycle (also known as Dungey cycle [16]) and related disturbances induce plasma instabilities, wave growth and wave-particle interactions, also giving rise to a wide range of global processes, including the build-up of storm-time ring current, the activation of the field-aligned current system and the auroral electrojects, the variability of radiation belt intensities, and enhanced particle precipitation into lower latitudes. Through such processes, the magnetospheric disturbances are projected down to the ionosphere. The stronger the southward IMF component and the stronger the solar wind velocity convecting the magnetic field, the more strongly the solar-wind-magnetosphere-ionosphere system is driven. This dependence is reflected in the magnetospheric energy input functions, such as the epsilon parameter of Akasofu, the most widely used one, according to which the solar wind energy input is determined by the solar wind speed, the IMF magnitude, and the so-called clock angle of the IMF orientation perpendicular to the Sun-Earth line [17; 18; 19]. The solar wind energy entering the magnetosphere is then dissipated via a variety of dynamic processes in the plasma sheet, the ring current and the ionosphere, with the latter being the dominant sink of the solar wind \begin{table}
\begin{tabular}{c c} \hline \hline
**Dst min (nT), Range** & **Storm Intensity** \\ \hline \(-\)30 to \(-\)50 & Weak \\ \hline \(-\)50 to \(-\)100 & Moderate \\ \hline \(<\)\(-\)100 & Intense \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Classification of storm events. Figure 1: The smoothed monthly solar sunspot number provided by the World Data Center(WDC) Sunspot Index and Long-Term Solar Observations (SILSO) in Royal Observatory of Belgium and the smoothed 10.7 cm radio flux provided by SWPC (Space Weather Prediction Center) in NOAA (National Oceanic and Atmospheric Administration) for the time interval 2008–2020. Solar cycle 24 started in December 2008, following a deep and long solar minimum. It reached its maximum in April 2014 and ended in December 2019.  
energy input through storm currents and particle precipitation, both contributing to the heating of the upper atmosphere. This energy dissipation in the high-latitude ionosphere generates numerous upper atmospheric changes that affect all state parameters. Key mechanisms which are the main sources of geo-effective solar wind flows include [6; 7; 8; 9; 10; 11; 12; 13; 14; 15]: (i) coronal mass ejections (CMEs) and the interplanetary CMEs (ICMEs), the evolutionary part of CMEs as they propagate through interplanetary space, as well as fast sheaths and shocks upstream of CMEs/ICMEs. Such structures occur more often near the solar maximum, carrying embedded southward-directed IMF at the Earth's vicinity. (ii) High-speed (-750-800 km/s) solar wind streams (HSSs) emanating from solar coronal holes and corotating interaction regions (CIRs).