Van Allen Probes measurements revealed the presence of the most unusual structures in the ultra‐relativistic radiation belts. Detailed modeling, analysis of pitch angle distributions, analysis of the difference between relativistic and ultra‐realistic electron evolution, along with theoretical studies of the scattering and wave growth, all indicate that electromagnetic ion cyclotron (EMIC) waves can produce a very efficient loss of the ultra‐relativistic electrons in the heart of the radiation belts. Moreover, a detailed analysis of the profiles of phase space densities provides direct evidence for localized loss by EMIC waves. The evolution of multi‐MeV fluxes shows dramatic and very sudden enhancements of electrons for selected storms. Analysis of phase space density profiles reveals that growing peaks at different values of the first invariant are formed at approximately the same radial distance from the Earth and show the sequential formation of the peaks from lower to higher energies, indicating that local energy diffusion is the dominant source of the acceleration from MeV to multi‐MeV energies. Further simultaneous analysis of the background density and ultra‐relativistic electron fluxes shows that the acceleration to multi‐MeV energies only occurs when plasma density is significantly depleted outside of the plasmasphere, which is consistent with the modeling of acceleration due to chorus waves.
The ionosphere is an ionized part of the upper atmosphere, spanning from 60 to around 1,000 km in altitude (Hargreaves, 1992). It arises mainly due to the photoionization effects from the solar extreme ultraviolet (EUV) radiation and charged energetic-particle precipitation (Kivelson & Russell, 1995). Generally, the ionosphere is strongly coupled with the thermosphere (Astafyeva, 2019). The latter supplies the neutral particles that can be ionized, and plays a crucial role in the interplay between the production (source) and recombination (loss) processes. The ionosphere affects the propagation of the Global Navigation Satellite System (GNSS) signals by introducing frequency-dependent delays. Unlike the neutral atmosphere, which can cause errors in navigation and positioning in the order of several meters, ionospheric effects can yield uncertainties of up to E 100 m (e.g., Hernández-Pajares et al., 2011;Petit & Luzum, 2010). Ionospheric delays are inversely related to the square of carrier frequency, and directly proportional to electron density integrated along the ray path (e.g., Goss et al., 2019;Hobiger & Jakowski, 2017).Electron density distribution in the ionosphere strongly depends on altitude and can be divided into several layers, originally identified from ionograms: the D-layer (60-90 km altitude), E-layer (90-130 km), and F-layer (above 130 km), which can be subdivided into F1 and F2 layers (e.g., Astafyeva, 2019). The dominant contribution to electron density profiles comes from the peak of the F2 layer, generally located between
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.