Relativistic electron flux dropouts in the outer radiation belt associated with corotating interaction regions

Abstract

Understanding how the relativistic electron fluxes drop out in the outer radiation belt under different conditions is of great importance. To investigate which mechanisms may affect the dropouts under different solar wind conditions, 1.5–6.0 MeV electron flux dropout events associated with 223 corotating interaction regions (CIRs) from 1994 to 2003 are studied using the observations of Solar, Anomalous, Magnetospheric Particle Explorer satellite. According to the superposed epoch analysis, it is found that high solar wind dynamic pressure with the peak median value of about 7 nPa is corresponding to the dropout of the median of the radiation belt content (RBC) index to 20% of the level before stream interface arrival, whereas low dynamic pressure with the peak median value of about 3 nPa is related to the dropout of the median of RBC index to 40% of the level before stream interface arrival. Furthermore, the influences of Russell‐McPherron effect with respect to interplanetary magnetic field orientation on dropouts are considered. It is pointed out that under positive Russell‐McPherron effect (+RM effect) condition, the median of RBC index can drop to 23% of the level before stream interface arrival, while for negative Russell‐McPherron effect (−RM effect) events, the median of RBC index only drops to 37% of the level before stream interface arrival. From the evolution of phase space density profiles, the effect of +RM on dropouts can be through nonadiabatic loss.

The Effects of Geomagnetic Storms and Solar Wind Conditions on the Ultrarelativistic Electron Flux Enhancements

“…Their results suggest that, for radiation belt electrons, CIR‐driven storms are more likely to produce flux enhancements at higher L * , while CME‐driven storms tend to cause deeper penetration of flux enhancements. Yuan and Zong (, ) and Yuan et al () studied the effects of CME‐ and CIR‐driven storms on relativistic electrons in the outer belt and found that in terms of flux enhancements and dropouts CME‐ and CIR‐driven storms have their own distinct features in influencing the radiation belt electrons. Future work will be conducted on further examining the effectiveness of different solar wind drivers on the ultrarelativistic electron flux enhancements especially regarding their energy‐dependent behaviors.…”

“…Previous studies have focused on the effect of geomagnetic storms on the outer radiation belt electrons in the energy range of approximately hundreds of keV to approximately 3 MeV (e.g., Anderson et al, ; Baker et al, ; Borovsky & Denton, ; Horne et al, ; Kataoka & Miyoshi, ; Kilpua et al, ; Kim et al, ; Li et al, ; Meredith et al, ; Murphy et al, ; Reeves, ; Reeves et al, ; Turner et al, ; Yuan et al, ; Yuan & Zong, , ; Zhao & Li, ). Reeves () studied 30 most intense radiation belt electron flux enhancement events during 1992–1995 using data from the Energetic Spectrometer for Particles on the geostationary satellite 1989‐046 and showed that every radiation belt electron flux enhancement event was associated with a geomagnetic storm but not all geomagnetic storms can cause radiation belt electron flux enhancements; while the maximum fluxes and minimum Dst index (as a proxy of geomagnetic storm intensity) is roughly correlated, large variations exist.…”

“…They found that CME‐driven storms produce more relativistic electrons than CIR‐driven storms in the whole outer radiation belt but the electron fluxes during CIR‐driven storms are much higher than those during CME‐driven storms at GEO. Also using electron flux data from SAMPEX, Yuan and Zong () and Yuan et al () performed superposed epoch analysis to 1.5‐ to 6‐MeV electron flux dropout events during CME‐driven and CIR‐driven storms, respectively, and found that high solar wind dynamic pressure and southward interplanetary magnetic field (IMF) can result in more significant dropouts during CME‐driven storms, while high solar wind dynamic pressure causes more significant electron flux dropouts during CIR‐driven storms, and under positive Russell‐McPherron effect the dropout is statistically more significant than that under negative Russell‐McPherron effect during CIR‐driven storms. Zhao and Li () studied the radiation belt electron flux variations during isolated geomagnetic storms from 1995 to 2004 using 2‐ to 6‐MeV electron flux data from SAMPEX.…”

Statistical Associations Between Geomagnetic Activity, Solar Wind, Solar Proton Events, and Winter NAO and AO Indices

“…Previously, it was shown that Kp positively correlated with the auroral electron flux (Hardy et al., 1987). Besides, EEPs were related to a higher SWS and Np (Asikainen & Ruopsa, 2016; Gao et al., 2015), GS (Longden et al., 2008; Meredith et al., 2011), and Stream Interaction Regions (Yuan et al., 2015). The SWS determines the energetic electron flux precipitating from the radiation belts at subauroral latitudes (Tinsley, 2008; Zhou et al., 2014).…”

The Efficiency of Coronal Mass Ejection With Different IMF Preconditions on the Production of Megaelectronvolt Electron Content in the Outer Radiation Belt

“…A great number of statistical studies on responses of the outer radiation belt to CMEs and CIRs were conducted during the last 20 years (e.g., Kataoka & Miyoshi, ; Miyoshi & Kataoka, ; O'Brien et al, ; Yuan & Zong, , ; Yuan et al, ). Yuan and Zong () statistically analyzed 2‐ to 6‐MeV electron fluxes during CME‐ and CIR‐driven magnetic storms from 1993 to 2003, using data from SAMPEX.…”