Dynamic responses of the Earth's radiation belts during periods of solar wind dynamic pressure pulse based on normalized superposed epoch analysis

Abstract

Using the electron flux measurements obtained from five satellites (GOES 15 and POES 15, 16, 18, and 19), we investigate the flux variations of radiation belt electrons during forty solar wind dynamic pressure pulses identified between September 2012 and December 2014. By utilizing the mean duration of the pressure pulses as the epoch timeline and stretching or compressing the time phases of individual events to normalize the duration by means of linear interpolation, we have performed normalized superposed epoch analysis to evaluate the dynamic responses of radiation belt energetic electrons corresponding to various groups of solar wind and magnetospheric conditions in association with solar wind dynamic pressure pulses. Our results indicate that by adopting the timeline normalization we can reproduce the typical response of the electron radiation belts to pressure pulses. Radiation belt electron fluxes exhibit large depletions right after the Pdyn peak during the periods of northward interplanetary magnetic field (IMF) Bz and are more likely to occur during the Pdyn pulse under southward IMF Bz conditions. For the pulse events with large negative values of (Dst)min, radiation belt electrons respond in a manner similar to those with southward IMF Bz, and the corresponding postpulse recovery can extend to L ~ 3 and exceed the prepulse flux levels. Triggered by the solar wind pressure enhancements, deeper earthward magnetopause erosion provides favorable conditions for the prompt electron flux dropouts that extend down to L ~ 5, and the pressure pulses with longer duration tend to produce quicker and stronger electron flux decay. In addition, the events with high electron fluxes before the Pdyn pulse tend to experience more severe electron flux dropouts during the course of the pulse, while the largest rate of electron flux increase before and after the pulse occurs under the preconditioned low electron fluxes. These new results help us understand how electron fluxes respond to solar wind dynamic pressure pulses and how these responses depend on the solar wind and geomagnetic conditions and on the preconditions in the electron radiation belts.

Understanding the Mechanisms of Radiation Belt Dropouts Observed by Van Allen Probes

“…Usually, the effect of magnetopause shadowing is evaluated by calculating the magnetopause position (e.g., Ni et al, ; Xiang et al, ). In this study, we find that the LCDS is a much more reliable index than the magnetopause position in estimating the scope of magnetopause shadowing and understanding the responses of radiation belt electrons.…”

Radiation Belt Slot Region Filling Events: Sustained Energetic Precipitation Into the Mesosphere

“…The Earth's radiation belts (or Van Allen belts) are formed by the drift orbits of energetic electrons confined by the Earth's magnetosphere and generally appear as two torus‐shaped regions (Van Allen, ). The outer belt is highly dynamic, responding strongly to solar wind driving during geomagnetic storms (e.g., Li et al, ; Ni et al, ; Reeves et al, ), occasionally splitting to form two rings (e.g., Baker et al, ; Mann et al, , , Shprits et al, ). This dynamic nature is controlled by a series of acceleration and loss mechanisms involving interactions with a range of magnetospheric waves (e.g., Horne et al , ; Li et al, ; Ni et al, ; Thorne, ; Thorne et al , ).…”

The effects of magnetospheric processes on relativistic electron dynamics in the Earth's outer radiation belt

“…Li et al, 2011;Reeves et al, 2011;Boynton et al, 2013;W. Li et al, 2013;Kim et al, 2015;Xiong et al, 2015;Ni et al, 2013aNi et al, , 2016Yu et al, 2015Yu et al, , 2016Wing et al, 2016]. However, these studies mainly discussed relativistic electron fluxes at geosynchronous orbit, which is well beyond the center of the outer radiation belt, and these changes of MeV electron fluxes included both nonadiabatic and adiabatic processes.…”