Rapid Enhancements of Relativistic Electrons in the Earth's Outer Radiation Belt Caused by the Intense Substorms: A Statistical Study

Abstract

The extreme and rapid variabilities of relativistic (≥1 MeV) electrons in the Earth's outer radiation belt are due to the acceleration and loss processes (e.g., L.

The Evolutions of the Seed and Relativistic Electrons in the Earth's Outer Radiation Belt During the Geomagnetic Storms: A Statistical Study

“…For the SL events, some unchanged or decreased events (R < 2) were observed at L* = 3.5 and 4.0 due to a lack the intense substorm activities during the main or recovery phases. These are consistent with previous studies (e.g., Jaynes et al, 2015;C. Tang et al, 2023;C.…”

“…In the present study, enhancements of the seed electron fluxes mainly occurred during the main phase, which was mainly caused by enhanced convection and substorm electron injections (e.g., C. L. Tang et al., 2018; Wang et al., 2022). And, enhancements of MeV electron flux for most ML and SL events mainly started to occur from the main phase, which was mainly caused by the interaction of the seed electrons with whistler mode chorus waves (e.g., C. Tang et al., 2023).…”

“…And previous studies have already provided simultaneous observational evidences that Electromagnetic ion cyclotron (EMIC) waves can cause relativistic (∼MeV) electron precipitations (e.g., Carson et al., 2013; Clilverd et al., 2015; Kersten et al., 2014; Miyoshi et al., 2008; Y. Y. Shprits et al., 2013, 2016; Su et al., 2016; Usanova et al., 2014; Zhang et al., 2016). Some studies have shown that the local acceleration by chorus waves during the storm main phase can accelerate electrons to relativistic energies, which results in the loss of the seed electrons (e.g., W. Li et al., 2014; C. Tang et al., 2023). Usually, the fluxes of MeV electrons in the outer radiation belt can increase during the recovery phase due to the DST effect and different acceleration processes.…”

“…. Some studies have shown that the local acceleration by chorus waves during the storm main phase can accelerate electrons to relativistic energies, which results in the loss of the seed electrons (e.g., W. Li et al, 2014;C. Tang et al, 2023).…”

Upper Limit on Outer Radiation Belt Electron Flux Based on Dynamical Equilibrium

“…Strong substorms with Kp ∼ 5-6 and AE ∼ 600-1,000 nT usually correspond to a time-and MLT-averaged chorus wave power 𝐴𝐴 ⟨𝐵𝐵 2 𝑤𝑤 ⟩𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 ∼ (50) 2 pT 2 at latitudes λ ∼ 15° of cyclotron resonance with 100 keV electrons near the loss-cone at L ∼ 5-6 (Agapitov et al, 2018). To reduce the lifetime τ L to its minimum value, τ SD (E min ) ∼ 140 s, the average wave power must increase up to 𝐴𝐴 ⟨𝐵𝐵 2 𝑤𝑤 ⟩𝑡𝑡 ∼ (280) 2 pT 2 , a level sometimes observed for hours at L ∼ 5 during geomagnetic storms and substorms (Chakraborty et al, 2022;Elliott et al, 2022;C. Tang et al, 2023), or during microbursts (Zhang et al, 2022).…”