In Situ Observations of the Formation of Periodic Collisionless Plasma Shocks from Fast Mode Waves

It has been long theorized, but not directly observed, that low-frequency magnetosonic plasma waves can steepen and form shocks. We show an example of small-amplitude, sinusoidal magnetosonic waves at the proton gyrofrequency upstream of the Martian bow shock. We hypothesize that these waves are pro...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2020-01, Vol.888 (2), p.L17
Main Authors: Shan, Lican, Du, Aimin, Tsurutani, Bruce T., Ge, Yasong S., Lu, Quanming, Mazelle, Christian, Huang, Can, Glassmeier, Karl-Heinz, Henri, Pierre
Format: Article
Language:English
Subjects:
Amplitudes
Charge exchange
Collisionless plasmas
Free energy
Gyrofrequency
Hydrogen
Hydrogen atoms
Hydrogen storage
Ion beams
Ionization
Photoionization
Pickup ions
Plasma physics
Plasma waves
Protons
Sciences of the Universe
Shocks
Solar wind
Solar wind flow
Solar wind protons
Space plasmas
Waves
Wind flow
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Summary:It has been long theorized, but not directly observed, that low-frequency magnetosonic plasma waves can steepen and form shocks. We show an example of small-amplitude, sinusoidal magnetosonic waves at the proton gyrofrequency upstream of the Martian bow shock. We hypothesize that these waves are produced by an ion beam instability associated with the ionization of hydrogen atoms by charge exchange with solar wind protons, solar photoionization, and/or electron impact ionization. As the waves are convected toward the planet by solar wind flow, the wave amplitude grows due to additional free energy put into the system by further ion beam particles. Finally, the steepened waves form shocks. Because of their development, the shocks are periodic with the separation at the proton gyroperiod. These observations lead to the conclusion that newborn ions may play a crucial role in the formation process of some collisionless plasma shocks in astrophysical and space plasmas.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/ab5db3