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.

Changes in and Recovery of the Turbulence Properties in the Magnetosheath for Different Solar Wind Streams

“…On the other hand, the properties of turbulence associated with the Fast SW streams and CIRs change only at the MHD scales at the dayside MSH. The SW speed is known to play one of the key roles in the magnetospheric response [6]. The unchanged kinetic-scale properties of turbulence during Fast streams may be related to the corresponding geoefficiency.…”

“…Various large-scale interplanetary phenomena may be distinguished by different kinetic and magnetic energy, deviations in the interplanetary magnetic field (IMF) vector from the ecliptic plane, and the SW speed. While the increased geoefficiency of the disturbed SW streams (interplanetary coronal mass ejections (ICMEs) including compressed regions (Sheath) ahead, corotating interaction regions (CIRs)) are generally known [1][2][3][4][5][6], the most significant factors and direct processes that underlie the difference in the magnetosphere response are still debated.…”

“…Exploration of the SW effects on the magnetosphere is usually prepared with the help of statistics from the SW measurements [5][6][7][8]. However, there is a magnetosheath (MSH) in front of the magnetopause that modifies the SW and IMF parameters substantially.…”

“…The properties of turbulent fluctuations can be analyzed as a proxy for the leading processes at different scales. Typically, in the undisturbed SW, the frequency spectrum of turbulent fluctuations follows the f −1 power law at the scales above ~10 6 km, then breaks and follows the f −5/3 law up to the ion scales (inertial range or MHD scales). At the ion scales (around proton gyroradius or proton inertial length), the spectrum breaks and transition to ion kinetic scales occurs.…”

Statistical study of electron density turbulence and ion-cyclotron waves in the inner heliosphere: Solar Orbiter observations

“…This suggests the possible presence of large-scale modulations, which may affect the Fourier spectra but are controlled well by the HSA. In order to achieve robust estimate, the scaling exponent of the qth Hilbert spectrum L q ( f ) was evaluated via the residual resampling (bootstrapping) procedure (Bradley & Robert 1994;Carbone et al 2020b). First, a least square fit is performed on each L q ( f ), then the residuals are randomly resampled and added to the fit, generating a new data-set (replica).…”