The Seed Populations in the Earth's Outer Radiation Belt During the Main Phase of Magnetic Storms: A Statistical Study

Abstract

Using the data from Van Allen Probes, we investigate in detail the seed populations in the outer radiation belt during the storm main phase. Based on the different flux variations of the seed electrons before the storm and around the storm peak, these storm events are divided into “flux decay events,” “flux enhancement events” and “strong flux enhancement events.” For flux decay events, a shorter storm main phase (≤12 hr) and smaller southward interplanetary magnetic field (IMF) and solar wind electric field (−15 nT < Bzmin < −5 nT, 2 mV/m < Eymax < 7 mV/m) are found. For flux enhancement events, large southward Bzmin and Eymax (−29 nT < Bzmin < −10 nT, 5 mV/m < Eymax < 11 mV/m) for the shorter main phase or smaller southward Bzmin and Eymax (−23 nT < Bzmin < −5 nT, 3 mV/m < Eymax < 11 mV/m) for the longer main phase (>12 hr) are observed. For strong flux enhancement events, larger southward Bzmin and Eymax (−32 nT < Bzmin < −13 nT, 5 mV/m < Eymax < 22 mV/m) for the shorter main phase or smaller southward Bzmin and Eymax (−26 nT < Bzmin < −9 nT, 3 mV/m < Eymax < 16 mV/m) for the longer main phase are observed. These suggest that the flux variations of the seed electrons during the storm main phase are highly influenced by the duration of the storm main phase, southward IMF, and solar wind electric field.

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

“…The chorus waves are well correlated with substorm intensity (e.g., Agapitov et al., 2013; Kim et al., 2015; Meredith et al., 2001, 2012; D. Wang et al., 2019). During the intense substorms, substorm electron injections or magnetospheric convection also provide the seed populations (e.g., Gabrielse et al., 2012; Khoo et al., 2019; Tang et al., 2013; X. Wang et al., 2022; Zhao et al., 2016), which can be energized to MeV energies by wave‐particle interactions (e.g., W. Li et al., 2014; Thorne et al., 2013). However, Meredith et al.…”

“…The acceleration mechanisms of relativistic electrons are mainly local acceleration and inward radial diffusion. For the local acceleration process, the seed electrons (∼hundred kiloelectron volts) from substorm injections or magnetospheric convection (e.g., Tang et al., 2009, 2018; X. Wang et al., 2022) are locally accelerated to relativistic energies by whistler‐mode chorus waves (e.g., Boyd et al., 2014; Horne & Thorne, 1998; L. Y. Li et al., 2005; Miyoshi et al., 2013; Mourenas et al., 2014; Omura et al., 2015). Previous studies have also shown that the local acceleration process involved energetic electrons in nonlinear interactions with chorus waves (e.g., Foster et al., 2017; Mozer et al., 2014).…”

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

“…L. Tang et al, 2017b;Turner et al, 2015Turner et al, , 2019. Wang et al (2022) have shown that the flux variations of the seed electrons during the storm main phase are highly influenced by the duration of the storm main phase, southward IMF, and solar wind electric field. Turner et al (2019) suggested the seed electron fluxes at ∼3 ≤ L ≤ ∼ 4 increased during the main phase of most magnetic storms and then decayed gradually during the recovery phase.…”

“…Previous studies have shown that the seed populations (100s keV) in the outer radiation belt have different generation or acceleration mechanisms. Usually, the seed populations mainly come from storm convection and substorm electron injections (e.g., Baker et al., 2016; Kissinger et al., 2014; Y. Y. Shprits et al., 2015; C. L. Tang et al., 2010, 2013, 2018; Tang, Zhou, et al., 2016; Wang et al., 2022). The chorus waves (e.g., Ma et al., 2016), fast magnetosonic waves (Turner et al., 2015), and ULF waves (e.g., C. L. Tang et al., 2018) can contribute to the generation of the seed populations.…”

“…L. Tang et al, 2017a;Turner et al, 2015Turner et al, , 2019Wing et al, 2016;Zhao et al, 2017Zhao et al, , 2019. Using the data from the Van Allen Probes, Wang et al (2022) statistically studied the seed populations in the outer radiation belt during the storm main phase. They found that the seed electrons during the main phase would decrease or increase, which was mainly affected by the southward interplanetary magnetic field (IMF), solar wind electric field, and the duration of the storm main phase.…”