On the Similarity and Repeatability of Fast Radiation Belt Loss: Role of the Last Closed Drift Shell

Abstract

Since the discovery of the Earth's Van Allen radiation belts over 50 years ago (Van Allen & Frank, 1959), determining the physical processes responsible for their dynamics have been a major focus of space physics research (e.g., Friedel et al., 2002). The dynamics of the trapped relativistic electron population with energies from hundreds of kilo electronvolts (∼100 keV) to millions of electronvolts (∼1 MeV) during geomagnetic storms is of particular interest because of their potential impact on satellite electronics through deep-dielectric charging (Baker et al., 1994). Electrons can be lost at the beginning of the storm before the subsequent acceleration of a source population to MeV energies, which can partially or completely replace those which are lost, in some cases creating radiation orders of magnitude stronger than that which existed pre-storm (e.g., Reeves et al., 2003). In particular, interaction with high-frequency plasma waves, such as chorus (e.g., Lee et al., 2013;Shprits et al., 2007), electromagnetic ion cyclotron (EMIC) (e.g., Ukhorskiy et al., 2010;Usanova et al., 2014), or plasmaspheric hiss (e.g., Thorne et al., 1973) waves, can cause loss into the atmosphere. Meanwhile, ultra-low frequency (ULF) plasma waves (Mann et al., 2016) can cause particles to be transported outwards to the last closed drift shell (LCDS) and lost at the magnetopause into the solar wind in a process known as magnetopause shadowing (e.g., Olifer et al., 2018;Turner et al., 2012). The relative importance of these processes continues to be hotly debated (Mann et al., 2018;Shprits et al., 2018). This paper, in particular, focuses on investigating whether the LCDS dynamics can explain the fast magnetopause shadowing losses.Recent studies have shown that a compression of the outer magnetospheric boundary can cause intense electron radiation belt losses occurring on very short ( 𝐴𝐴 𝐴 1 day) timescales. For example, Olifer et al. ( 2018) showed that the LCDS location of the Van Allen belt electrons and its dynamics can explain rapid and intense dropouts of relativistic electrons in some of the most intense geomagnetic storms of the last decade. It is also interesting to investigate on a statistical basis whether a substantial compression of the magnetopause, characterized by inward motion of the LCDS, can cause a radiation belt dropout in every storm and

Electron Flux Variability and Ultra‐Low Frequency Wave Activity in the Outer Radiation Belt Under the Influence of Interplanetary Coronal Mass Ejections and High‐Speed Solar Wind Streams: A Statistical Analysis From the Van Allen Probes Era

“…The time to flux change one order of magnitude from t 0 is from 6 to 12 hr for ICME and ∼12 to ∼20 hr for HSS. (Olifer et al., 2021) studied on the losses of Van Allen Radiation Belts and LCDS during geomagnetic storms. They showed the relation of magnetopause shadowing to rapid and strong losses in the outer radiation belt, up to two orders of magnitude.…”

“…• Interplanetary coronal mass ejections (ICMEs) related flux variation happens faster, while the High-Speed solar wind streams (HSSs)-related happens gradually, starting from higher to lower L* values • Southward interplanetary magnetic field Bz, enhanced AE index, and high solar wind speed variations are commonly associated with flux enhancement • Ultra-low frequency diffusion coefficients are stronger and have a longer duration for enhancements than depletion during both ICME and HSS events interaction with ULF waves, can be related to the depletion in the outer radiation belt electrons by the outward radial diffusion and magnetopause shadowing mechanisms (Jaynes et al, 2015;Olifer et al, 2018Olifer et al, , 2021Souza et al, 2017;Tu et al, 2019;Turner et al, 2012).…”

Depletions of Multi‐MeV Electrons and Their Association to Minima in Phase Space Density

“…To ascertain the role EMIC wave-driven loss plays in the overall depletions in radiation belt flux, the depletion events identified in Section 3.4 are compared with the observed PSD minima. The first row in Figure 4 radial diffusion and magnetopause shadowing (e.g., Drozdov et al, 2019;Fei et al, 2006;Olifer, Mann, Ozeke, Claudepierre, et al, 2021;Pierrard et al, 2020Pierrard et al, , 2021Xiang et al, 2017). The number of depletion events at L* > 5 decreases with increasing energy, because high-energy electrons occur less frequently in the radiation belts.…”

Modeling Radiation Belt Electron Dropouts During Moderate Geomagnetic Storms Using Radial Diffusion Coefficients Estimated With Global MHD Simulations

“…On the other hand, the actual gradient of electron PSD could have been steeper than that simulated for Case 1, increasing outward diffusion and loss. It should be noted that the Van Allen Probes measurements used for the initial PSD gradient are limited in time accuracy (e.g., Olifer et al (2021)) due to the 4-hr time steps of data acquisition within L* = 3 − 6. Furthermore, updating the outer boundary condition at L* = 6 with GOES data does not guarantee that the simulated PSD gradient was equivalent to the real one in that L* domain at an instant of time since this gradient highly depends on the evolution of actual radial diffusion rates and also on the evolution of the actual and unknown PSD gradient near and just above L* = 6 (Ozeke et al, 2018).…”