Rapid enhancement of low‐energy (<100 eV) ion flux in response to interplanetary shocks based on two Van Allen Probes case studies: Implications for source regions and heating mechanisms

Abstract

Interactions between interplanetary (IP) shocks and the Earth's magnetosphere manifest many important space physics phenomena including low‐energy ion flux enhancements and particle acceleration. In order to investigate the mechanisms driving shock‐induced enhancement of low‐energy ion flux, we have examined two IP shock events that occurred when the Van Allen Probes were located near the equator while ionospheric and ground observations were available around the spacecraft footprints. We have found that, associated with the shock arrival, electromagnetic fields intensified, and low‐energy ion fluxes, including H+, He+, and O+, were enhanced dramatically in both the parallel and perpendicular directions. During the 2 October 2013 shock event, both parallel and perpendicular flux enhancements lasted more than 20 min with larger fluxes observed in the perpendicular direction. In contrast, for the 15 March 2013 shock event, the low‐energy perpendicular ion fluxes increased only in the first 5 min during an impulse of electric field, while the parallel flux enhancement lasted more than 30 min. In addition, ionospheric outflows were observed after shock arrivals. From a simple particle motion calculation, we found that the rapid response of low‐energy ions is due to drifts of plasmaspheric population by the enhanced electric field. However, the fast acceleration in the perpendicular direction cannot solely be explained by E × B drift but betatron acceleration also plays a role. Adiabatic acceleration may also explain the fast response of the enhanced parallel ion fluxes, while ion outflows may contribute to the enhanced parallel fluxes that last longer than the perpendicular fluxes.

The Characteristic Response of Whistler Mode Waves to Interplanetary Shocks

“…Meanwhile, the thermal plasma is adiabatically heated mainly in the perpendicular direction resulting in an increase in the electron anisotropy. Subsequently, geomagnetic activity is broadly enhanced, which includes the appearance of many wave phenomena and substorm injections (e.g., Yue et al, , ; Yue, Li, ; Yue & Zong, ). Previously, Zhou et al () have shown that chorus waves at the dayside magnetosphere are excited after the IP shock arrival.…”

Near‐Earth Solar Wind: Plasma Characteristics From ARTEMIS Measurements

“…In addition to magnetic field amplitude and orientation, the solar wind, a supersonic plasma, is characterized by its dynamic pressure, Mach number, and ion and electron temperatures. These parameters can be combined to calculate different complex coupling functions describing the efficiency of solar wind‐driven magnetosphere dynamics (e.g., Balikhin et al, ; Borovsky et al, , and references therein) or can be used alone to investigate the impact of the solar wind on the magnetosphere (e.g., Sergeev et al, ; Yue et al, , and references therein).…”

Cold Plasmaspheric Electrons Affected by ULF Waves in the Inner Magnetosphere: A Van Allen Probes Statistical Study

“…Breneman et al () found that the modulation of main plasmaspheric populations by ULF waves may affect the spatial and temporal dynamics of radiation belt electron losses. Approximately electron volt ions (e.g., H + , He + , and O + ) can be heated up to tens to hundreds of electron volts by ULF wave electric field due to the E × B convective motion (Yue et al, ; Zong et al, ). The dynamics of cold plasmaspheric particles have important impact on the magnetospheric processes by affecting the excitation, propagation, and distribution of various waves (e.g., hiss, chorus, and electromagnetic ion cyclotron waves; e.g., Breneman et al, ; Dai et al, ; Fraser & Nguyen, ; Li et al, ; Malaspina et al, ) and magnetic reconnections at the magnetopause (e.g., Walsh, Foster, et al, ; Walsh, Phan, et al, ).…”

“…Energy input to Earth's magnetosphere from the Sun is controlled by solar wind and interplanetary magnetic field, part of which is mediated by ultralow‐frequency (ULF) waves in the frequency range of 1 mHz to 1 Hz. ULF waves can propagate electromagnetic energy over the magnetosphere and into the ionosphere and play a crucial role in the acceleration and transportation of energetic particles in the radiation belt and ring current (e.g., Claudepierre et al, ; Mann, ; Min et al, ; Takahashi et al, ; Ukhorskiy et al, ; Zong, Rankin, et al, ) and cold particles in the plasmasphere (e.g., Ren, Zong, Miyoshi, et al, ; Ren et al, ; Yue et al, ; Zong, Wang, et al, ). Previous studies have demonstrated that the drift‐bounce resonant particles around the magnetic equator exhibit bidirectional pitch angle distributions (e.g., Ren et al, ; Takahashi et al, ; Yang, Zong, Fu, Takahashi, et al, ), and the off‐equator resonant particles will show pitch angle dispersion signatures (e.g., Ren, Zong, Zhou, et al, ; Yang, Zong, Fu, Takahashi, et al, ).…”