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- Title
Acceleration of Interstellar Pickup He<sup>+</sup> at Earth's Perpendicular Bow Shock.
- Authors
Starkey, M. J.; Fuselier, S. A.; Desai, M. I.; Burch, J. L.; Gomez, R. G.; Mukherjee, J.; Russell, C. T.; Lai, H.; Schwartz, S. J.
- Abstract
On 05 December 2015 the Magnetospheric MultiScale constellation observed interstellar pickup ion distributions during an inbound crossing of Earth's perpendicular bow shock near the subsolar point, which provides new insights into shock acceleration of pickup ions throughout the heliosphere. In this study we analyze the upstream and downstream velocity distributions of H+ and He+ using data from the Hot Plasma Composition Analyzer on Magnetospheric MultiScale. We derive average two‐dimensional pitch angle distributions in the upstream and downstream field‐aligned bulk plasma frame, as well as integrated one‐dimensional velocity distributions. By comparing the upstream and downstream distributions, we find evidence of accelerated H+ and He+ downstream of the shock. By comparing measured and theoretical reflection ratios for He+, we attribute a significant part of this acceleration to a single reflection at the shock. Plain Language Summary: By studying distributions of ions before and after a shock in space, we gain valuable insights into shock acceleration mechanisms that produce high‐energy ion populations, observed throughout the heliosphere. On 05 December 2015 the Magnetospheric MultiScale constellation crossed Earth's perpendicular bow shock and measured velocity distributions of He+ ions before and after the shock. This study analyzes these distributions in search for signs of accelerated He+. We find that He+ is accelerated mainly perpendicular to the local magnetic field, and that a significant fraction of the accelerated He+ is consistent with the theory of shock reflection at the bow shock, in which an ion is reflected at the shock and then energized by the solar wind electric field (pointing parallel to the shock surface) as the ion gyrates back to the shock. Key Points: MMS observed interstellar pickup He+ upstream and downstream of the Earth's perpendicular bow shockComparison of upstream and downstream velocity distributions revealed accelerated pickup He+The observations are consistent with single reflection shock acceleration
- Subjects
MAGNETOSPHERE; BOW shock (Astrophysics); HELIUM ions; SOLAR wind; VELOCITY distribution (Statistical mechanics)
- Publication
Geophysical Research Letters, 2019, Vol 46, Issue 19, p10735
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2019GL084198