Speaker
Description
The Earth’s inner magnetosphere can exhibit significant variability in the plasma density, which directly influences wave propagation in this environment. These waves play a central role in the dynamics of the relativistic and ultra-relativistic radiation belts' electron flux. Changes in plasma density, such as those occurring in the plasmasphere region, impact the group velocity of waves and, consequently, the resonant interactions with electrons, influencing both acceleration and loss mechanisms. To study how density variations affect the dynamics of ultra-relativistic electrons, this work analyzed an event that occurred from August 15 to 30, 2018, using multi-satellite data observations. Interplanetary medium conditions data is obtained from OMNIweb, which provides information on solar wind speed and density, as well as the behavior of the interplanetary magnetic field (IMF). In the inner magnetosphere, the Van Allen Probes (RBSP) mission was employed to measure the electron flux in different energy ranges, up to ultra-relativistic levels, and to estimate the plasma density, with a special focus on the evolution of electrons with energy around ~5.2 MeV. The results show that, by the end of August 25, an interplanetary coronal mass ejection (ICME) hit the Earth's magnetosphere, starting a geomagnetic storm. Due to the coupling between the ICME and the magnetosphere, a strong dropout of ultra-relativistic electron fluxes was observed. Approximately 24 hours later, on August 26, a high-speed solar wind stream (HSS), with speeds around 550 km/s, maintained magnetospheric activity for about 20 hours. During this period, an increase of about three orders of magnitude in the ~5.2 MeV electron flux was observed in inner regions as L ≈ 3.5, indicating efficient re-energization of the ultra-relativistic electron population. In the density measurements, a plasmaspheric plume was also identified, characterized by a localized increase in plasma density. This plume, resulting from the erosion and subsequent refilling of the plasmasphere, may have influenced wave propagation and affected their interaction with energetic particles. The ICME disturbance in the Earth's magnetosphere, followed by the HSS arrival and sustained impinged high speed, favors an environment conducive to both the initial loss and subsequent acceleration of ultra-relativistic electrons. Based on these observations, it is suggested that compound events, such as the sequential occurrence of an ICME and HSS, along with density variations, can play an important role in ultra-relativistic electron dynamics. Therefore, a detailed analysis of this dynamic in the plasmasphere under the influence of a complex solar wind structure will be shown in this work.
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