# Modulation of Solar Wind Impact on the Earth's Magnetosphere during the Solar Cycle
###### Abstract  
The understanding of extreme geomagnetic storms is one of the key issues in space weather. Such phenomena have been receiving increasing attention, especially with the aim of forecasting strong geomagnetic storms generated by high-energy solar events since they can severely perturb the near-Earth space environment. Here, the disturbance storm time index \(Dst\), a crucial geomagnetic activity proxy for Sun-Earth interactions, is analyzed as a function of the energy carried by different solar wind streams. To determine the solar cycle activity influence on \(Dst\), a 12-year dataset was split into sub-periods of maximum and minimum solar activity. Solar wind energy and geomagnetic activity were closely correlated for both periods of activity. Slow wind streams had negligible effects on Earth regardless of their energy, while high-speed streams may induce severe geomagnetic storming depending on the energy (kinetic or magnetic) carried by the flow. The difference between the two periods may be related to the higher rate of geo-effective events during the maximum activity, where coronal mass ejections represent the most energetic and geo-effective driver. During the minimum period, despite a lower rate of high energetic events, a moderate disturbance in the \(Dst\) index can be induced. magnetohydrodynamics; solar wind; magnetosphere; heliosphere 25 April 202210 June 202210  
the origin of geomagnetic storms (GSs), which have important effects on our technological society, and possibly affect climate conditions through complex interactions with the Earth's atmosphere. When a CME or an HSS impacts the Earth system, it destabilizes the magnetosphere, generating a GS [4]. During a GS, the main magnetospheric currents and the connected ionospheric currents are intensified, causing rapid changes in the geomagnetic field. These variations generate geomagnetically induced currents (GICs) that can severely damage the operation of power grids, magnetic surveying, etc. [5]. Moreover, GSs also heat the ionosphere, changing its density and composition and perturbing signals propagating through this region, such as radio and global navigation satellite system communications [6]. These effects can seriously affect our technological society, and deserve to be thoroughly investigated. The Earth's magnetosphere is continuously connected to the ionosphere. The magnetosphere-ionosphere system represents an active element that exhibits very complex dynamics (see [7], and references therein). The response of this system to changes in the interplanetary medium is non-linear, intermittent, and scale-invariant, showing several features common to open, extended stochastic systems, usually in an out-of-equilibrium configuration, near criticality [8; 9], manifested as across-scale coupling processes. These phenomena and processes, which are highly structured in space and time (e.g., wave dissipation, turbulence, electric field fluctuations), can produce effects at large scales. At the same time, large-scale phenomena create local conditions that can either promote or suppress the development of rapidly changing structures at small spatial scales (e.g., instabilities and turbulence). These features are observed during geomagnetic storms and sub-storms, which implies the occurrence of rapid variations in the geomagnetic field, auroral displays in the polar ionosphere [10] and fast intensification of atmosphere-ionosphere-magnetosphere (AIM) current systems [11]. However, despite the efforts of the scientific community [5; 12; 13], the understanding of the physical phenomena occurring in the circumterrestrial environment in response to geomagnetic storms is far from being complete. The intensity of a storm can be quantified by the disturbance storm time index, \(Dst\), which is a local time average of the depression measured along the magnetic equator. \(Dst\) is thus conventionally designed to estimate the ring current intensity and, in turn, to monitor the storm severity.