Simulations of inner magnetosphere dynamics with an expanded RAM-SCB model and comparisons with Van Allen Probes observations

Abstract Simulations from our newly expanded ring current-atmosphere interactions model with self-consistent magnetic field (RAM-SCB), now valid out to 9 R E, are compared for the first time with Van Allen Probes observations. The expanded model reproduces the storm time ring current buildup due to the increased convection and inflow of plasma from the magnetotail. It matches Magnetic Electron Ion Spectrometer (MagEIS) observations of the trapped high-energy (\u3e50 keV) ion flux; however, it underestimates the low-energy (\u3c10 keV) Helium, Oxygen, Proton, and Electron (HOPE) observations. The dispersed injections of ring current ions observed with the Energetic particle, Composition, and Thermal plasma (ECT) suite at high (\u3e20 keV) energy are better reproduced using a high-resolution convection model. In agreement with Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations, RAM-SCB indicates that the large-scale magnetic field is depressed as close as ∼4.5 RE during even a moderate storm. Regions of electromagnetic ion cyclotron instability are predicted on the duskside from ∼6 to ∼9 RE, indicating that previous studies confined to geosynchronous orbit may have underestimated their scattering effect on the energetic particles. Key Points Expanded RAM-SCB model reproduces well high-energy (\u3e50 keV) MagEIS observations The magnetic field is depressed as close as ∼4.5 RE during even a moderate storm EMIC wave growth extends on duskside from ∼6 to ∼9 RE during storm main phase

Applying the cold plasma dispersion relation to whistler-mode chorus waves:EMFISIS wave measurements from the Van Allen Probes

Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the the cold plasma dispersion relation in this context is tested using EMFISIS observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1-0.9 fce). Results from this study indicate that the calculated wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10¯3 nT2, using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater, 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons

Analysis of Magnetic Fields in Inertial Alfven Wave Collisions

Turbulence in astrophysical and space plasmas is dominated by the nonlinear interaction of counterpropagating Alfven waves. Most Alfven wave turbulence theories have been based on ideal plasma models, such as incompressible MHD, for Alfven waves at large scales. However, in the inertial Alfven wave regime (vA > vthe), relevant to magnetospheric plasmas, how the turbulent nonlinear interactions are modified by the dispersive nature of the waves remains to be explored. Here we present the first laboratory evidence of the nonlinear interaction in the inertial regime. A comparison is made with the theory for MHD Alfven waves.Comment: 2 pages, 1 figur

Quantifying the relative contributions of substorm injections and chorus waves to the rapid outward extension of electron radiation belt

Abstract We study the rapid outward extension of the electron radiation belt on a timescale of several hours during three events observed by Radiation Belt Storm Probes and Time History of Events and Macroscale Interactions during Substorms satellites and particularly quantify the contributions of substorm injections and chorus waves to the electron flux enhancement near the outer boundary of radiation belt. A comprehensive analysis including both observations and simulations is performed for the first event on 26 May 2013. The outer boundary of electron radiation belt moved from L = 5.5 to L \u3e 6.07 over about 6 h, with up to 4 orders of magnitude enhancement in the 30 keV to 5 MeV electron fluxes at L = 6. The observations show that the substorm injection can cause 100% and 20% of the total subrelativistic (∼0.1 MeV) and relativistic (2-5 MeV) electron flux enhancements within a few minutes. The data-driven simulation supports that the strong chorus waves can yield 60%-80% of the total energetic (0.2-5.0 MeV) electron flux enhancement within about 6 h. Some simple analyses are further given for the other two events on 2 and 29 June 2013, in which the contributions of substorm injections and chorus waves are shown to be qualitatively comparable to those for the first event. These results clearly illustrate the respective importance of substorm injections and chorus waves for the evolution of radiation belt electrons at different energies on a relatively short timescale. Key Points Rapid outward extension of electron radiation belt observed by RBSP and THEMIS A two-step scenario to explain the rapid flux enchantment Differentiating between contributions of substorm injections and chorus waves

The trapping of equatorial magnetosonic waves in the Earth’s outer plasmasphere

Abstract We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth\u27s plasmasphere. Intense equatorial magnetosonic waves were observed inside the plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosonic wave event, we demonstrate that magnetosonic waves can also be trapped within local density structures. We suggest that perpendicular wave propagation is important for explaining the presence of magnetosonic waves in the Earth\u27s plasmasphere at locations away from the generation region. Key Points Magnetosonic waves are excited by ion ring distributions near the plasmapauseMagnetosonic waves are trapped in a limited radial region in the plasmasphereMagnetosonic waves are modulated by local density structures