Simulated Magnetopause Losses and Van Allen Probe Flux Dropouts
Location
Yosemite National Park
Start Date
2-11-2014 9:20 AM
End Date
2-11-2014 9:50 AM
Description
Since the launch of the twin Van Allen Probes spacecraft 30 August 2012, superb data has become available against which to test models of outer zone radiation belt electron variability. Within the first forty days following launch, three MeV-electron flux dropout events were seen, along with disparate timescales for recovery and strong enhancement of electron flux extending up to 8.8 MeV in October 2012. The first two dropouts bracketed the ‘storage ring’ feature observed by the REPT instrument (Baker et al., Nature, 2013), which was the first particle detector to be commissioned on each spacecraft on 1 September. An interplanetary shock impacted the magnetosphere on 3 September, followed by depletion of outer zone electrons outside a radial distance of 3.5 RE in the equatorial plane. The residual ring of relativistic electrons remained between 3 and 3.5 RE, as the outer zone reformed at larger radial distances within the plasmsphere, until another interplanetary shock arrived on 1 October, removing both the storage ring and reformed outer zone. A third interplanetary shock caused further depletion of flux outside of 3 RE on 8 October, just prior to the strong flux enhancement seen at multi-MeV energies on 9 October. Simulations of these three flux depletion events, and a fourth on 17 March 2013, preceding another strong multi-MeV enhancement, have been performed using the Lyon-Fedder-Mobarry MHD code driven by upstream solar wind parameters measured by the ACE and WIND spacecraft, also coupled to the Rice Convection Model which includes drift physics. Analysis of the MHD fields shows inward motion of the magnetopause for all four events, along with enhanced ULF wave power in the outer magnetosphere. Guiding center test particle simulations of radiation belt electron response to the MHD fields provide evidence for loss due to magnetopause shadowing for these events. In particular, the ‘annihilation’ of the outer zone between 0600 – 1000 UT on 17 March reported by Baker et al. (Geophys. Res Lett., submitted, 2013b) is confirmed in our simulations. The severe plasmapause erosion which occurred for each of the four storms studied produced conditions conducive to scattering losses by whistler mode chorus and EMIC waves at low L values, augmenting magnetopause losses at higher L values.
Simulated Magnetopause Losses and Van Allen Probe Flux Dropouts
Yosemite National Park
Since the launch of the twin Van Allen Probes spacecraft 30 August 2012, superb data has become available against which to test models of outer zone radiation belt electron variability. Within the first forty days following launch, three MeV-electron flux dropout events were seen, along with disparate timescales for recovery and strong enhancement of electron flux extending up to 8.8 MeV in October 2012. The first two dropouts bracketed the ‘storage ring’ feature observed by the REPT instrument (Baker et al., Nature, 2013), which was the first particle detector to be commissioned on each spacecraft on 1 September. An interplanetary shock impacted the magnetosphere on 3 September, followed by depletion of outer zone electrons outside a radial distance of 3.5 RE in the equatorial plane. The residual ring of relativistic electrons remained between 3 and 3.5 RE, as the outer zone reformed at larger radial distances within the plasmsphere, until another interplanetary shock arrived on 1 October, removing both the storage ring and reformed outer zone. A third interplanetary shock caused further depletion of flux outside of 3 RE on 8 October, just prior to the strong flux enhancement seen at multi-MeV energies on 9 October. Simulations of these three flux depletion events, and a fourth on 17 March 2013, preceding another strong multi-MeV enhancement, have been performed using the Lyon-Fedder-Mobarry MHD code driven by upstream solar wind parameters measured by the ACE and WIND spacecraft, also coupled to the Rice Convection Model which includes drift physics. Analysis of the MHD fields shows inward motion of the magnetopause for all four events, along with enhanced ULF wave power in the outer magnetosphere. Guiding center test particle simulations of radiation belt electron response to the MHD fields provide evidence for loss due to magnetopause shadowing for these events. In particular, the ‘annihilation’ of the outer zone between 0600 – 1000 UT on 17 March reported by Baker et al. (Geophys. Res Lett., submitted, 2013b) is confirmed in our simulations. The severe plasmapause erosion which occurred for each of the four storms studied produced conditions conducive to scattering losses by whistler mode chorus and EMIC waves at low L values, augmenting magnetopause losses at higher L values.