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Impulsively Reflected Ions: A Plausible Mechanism for Ion Acoustic Wave Growth in Collisionless Shocks
Author(s) -
Goodrich Katherine A.,
Ergun Robert,
Schwartz Steven J.,
Wilson Lynn B.,
Johlander Andreas,
Newman David,
Wilder Frederick D.,
Holmes Justin,
Burch James,
Torbert Roy,
Khotyaintsev Yuri,
Lindqvist PerArne,
Strangeway Robert,
Gershman Daniel,
Giles Barbara
Publication year - 2019
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja026436
Subject(s) - ion , physics , shock wave , instability , shock (circulatory) , ion acoustic wave , population , bow shock (aerodynamics) , momentum (technical analysis) , bow wave , atomic physics , computational physics , acoustic wave , plasma , astrophysics , solar wind , mechanics , optics , nuclear physics , medicine , demography , finance , sociology , economics , quantum mechanics
Abstract We present recent high time resolution observations from an oblique (43°) shock crossing from the Magnetospheric Multiscale mission. Short‐duration bursts between 10 and 100 ms of ion acoustic waves are observed in this event alongside a persistent reflected ion population. High time resolution (150 ms) particle measurements show strongly varying ion distributions between successive measurements, implying that they are bursty and impulsive by nature. Such signatures are consistent with ion bursts that are impulsively reflected at various points within the shock. We find that, after instability analysis using a Fried‐Conte dispersion solver, the insertion of dispersive ion bursts into an already stable ion distribution can lead to wave growth in the ion acoustic mode for short durations of time. We find that impulsively reflected ions are a plausible mechanism for ion acoustic wave growth in the terrestrial bow shock and, furthermore, suggest that wave growth can lead to a small but measurable momentum exchange between the solar wind ions and the reflected population.