Speaker
Description
The Earth’s magnetosphere evolves dynamically under the influence of solar activity. The solar wind is a persistent stream of plasma carrying the interplanetary magnetic field and continuously interacts with the magnetosphere, governing its structure and behavior. Transient solar phenomena, such as Coronal Mass Ejections (CMEs) and High-Speed Solar Wind Streams (HSSs), further modulate this system. CMEs erupt from active regions on the Sun, ejecting vast quantities of plasma, while HSSs emerge from coronal holes and propagate at fast speeds. These events generate geomagnetic disturbances, detectable via ground-based magnetometers, which often escalate into storms and substorms. The Dst Index is a parameter that quantifies these events. It measures the fluctuation of the geomagnetic field’s horizontal component and presents a defined pattern during the occurrence of geomagnetic storms. Such transient events also produce magnetohydrodynamic (MHD) waves and inject charged particles into the magnetosphere. These injected particles are low-energy and can become trapped in the inner magnetosphere. Seed particles (200–500 keV electrons) may later be accelerated to relativistic energies, forming the outer Van Allen radiation belt around the planet. The primary focus of this study are the confined particles between ~3 and 7 Earth radii—particularly relativistic electrons (1.8–2.6 MeV). Given that particles trapped in a dipolar magnetic field are subject to variability, especially during solar wind disturbances, this work investigates two prolonged quiescent events of relativistic electron flux during distinct phases of solar activity. We inspect two events: the first spanning May 19 to June 9, 2015, during the declining phase of solar maximum, and the second from July 5 to 25, 2018, amid waning solar activity. It is already known that wave–particle interactions represent a dominant driver of electron flux variability. In addition, the dynamic mechanisms responsible for the respective dropouts and enhancements in both events are consistent with established literature. These include the clear influence of magnetopause shadowing and wave-particle interactions (Ultra-Low Frequency - ULF, chorus, and ElectroMagnetic Ion Cyclotron - EMIC waves) for the dropouts, as well as wave-particle interactions (ULF and chorus waves) for the enhancements. However, this work examines the physical processes that triggered the conditions sustaining the inner magnetosphere in a prolonged quiescent period during both distinct phases of solar activity. These findings highlight the importance to characterize the interplanetary conditions during quiescent relativistic electron flux in the outer radiation belt, and the distinct roles of solar wind structures in flux enhancement dynamics.
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