Ion acoustic waves at comet 67P/Churyumov-Gerasimenko

Abstract. Ion acoustic waves were observed between 15 and 30 km from the centre of comet 67P/Churyumov–Gerasimenko by the Rosetta spacecraft during its close flyby on 28 March 2015. There are two electron populations: one cold at kBTe≈0.2 eV and one warm at kBTe≈2 eV. The ions are dominated by a cold (a few hundredths of electronvolt) distribution of water group ions with a bulk speed of (3–3.7) km s−1. A warm kBTe≈6 eV ion population, which also is present, has no influence on the ion acoustic waves due to its low density of only 0.25 % of the plasma density. Near closest approach the propagation direction was within 50∘ from the direction of the bulk velocity. The waves, which in the plasma frame appear below the ion plasma frequency fpi≈2 kHz, are Doppler-shifted to the spacecraft frame where they cover a frequency range up to approximately 4 kHz. The waves are detected in a region of space where the magnetic field is piled up and draped around the inner part of the ionised coma. Estimates of the current associated with the magnetic field gradient as observed by Rosetta are used as input to calculations of dispersion relations for current-driven ion acoustic waves, using kinetic theory. Agreement between theory and observations is obtained for electron and ion distributions with the properties described above. The wave power decreases over cometocentric distances from 24 to 30 km. The main difference between the plasma at closest approach and in the region where the waves are decaying is the absence of a significant current in the latter. Wave observations and theory combined supplement the particle measurements that are difficult at low energies and complicated by spacecraft charging.

Download Full-text

Ion acoustic waves near a comet nucleus: Rosetta observations at comet 67P/Churyumov-Gerasimenko

10.5194/angeo-2020-59 ◽

2020 ◽

Author(s):

Herbert Gunell ◽

Charlotte Götz ◽

Elias Odelstad ◽

Arnaud Beth ◽

Maria Hamrin ◽

...

Keyword(s):

Acoustic Waves ◽

Propagation Direction ◽

Wave Power ◽

Comet Nucleus ◽

Frequency Range ◽

Ion Acoustic Waves ◽

Ion Acoustic ◽

The Waves ◽

Comet 67P ◽

Bulk Speed

Abstract. Ion acoustic waves were observed between 15 and 30 km from the centre of comet 67P/Churyumov-Gerasimenko by the Rosetta spacecraft during its close flyby on 28 March 2015. There are two electron populations: one cold at approximately 0.2 eV and one warm at approximately 4 eV. The ions are dominated by a cold (a few hundredths of eV) distribution with a bulk speed of (3–3.7) km/s. Near closest approach the propagation direction was within 50 degrees from the direction of the bulk velocity, leading to a Doppler shift of the waves that in the spacecraft frame cover a frequency range up to approximately 4 kHz. The wave power decreased over cometocentric distances from 24 to 30 km. The main difference between the plasma at closest approach and in the region where the waves are decaying is the absence of a significant current in the latter.

Download Full-text

The role of Cairns–Gurevich distributed electrons on obliquely propagating ion‐acoustic waves

Contributions to Plasma Physics ◽

10.1002/ctpp.202000225 ◽

2021 ◽

Author(s):

H. Bouziane ◽

K. Annou

Keyword(s):

Acoustic Waves ◽

Ion Acoustic Waves ◽

Ion Acoustic

Download Full-text

Dynamical study of nonlinear ion acoustic waves in presence of charged space debris at Low Earth Orbital (LEO) plasma region

Astrophysics and Space Science ◽

10.1007/s10509-020-03914-2 ◽

2021 ◽

Vol 366 (1) ◽

Author(s):

A. Mukherjee ◽

S. P. Acharya ◽

M. S. Janaki

Keyword(s):

Acoustic Waves ◽

Space Debris ◽

Plasma Region ◽

Ion Acoustic Waves ◽

Dynamical Study ◽

Ion Acoustic

Download Full-text

High time resolution PFISR and optical observations of naturally enhanced ion acoustic lines

Annales Geophysicae ◽

10.5194/angeo-27-1457-2009 ◽

2009 ◽

Vol 27 (4) ◽

pp. 1457-1467 ◽

Cited By ~ 13

Author(s):

R. G. Michell ◽

K. A. Lynch ◽

C. J. Heinselman ◽

H. C. Stenbaek-Nielsen

Keyword(s):

High Resolution ◽

Time Resolution ◽

Acoustic Waves ◽

Fast Moving ◽

High Time ◽

High Time Resolution ◽

Ion Acoustic Waves ◽

Raw Data ◽

Ion Acoustic ◽

Auroral Imaging

Abstract. Observations of naturally enhanced ion acoustic lines (NEIALs) taken with the Poker Flat Incoherent Scatter Radar (PFISR) using a mode with very high time resolution are presented. The auroral event took place over Poker Flat, Alaska on 8 February 2007 at 09:35 UT (~22:00 MLT), and the radar data are complemented by common-volume high-resolution auroral imaging. The NEIALs occurred during only one of the standard 15-s integration periods. The raw data of this time show very intermittent NEIALs which occur only during a few very short time intervals (≤1 s) within the 15-s period. The time sampling of the raw data, ~19 ms on average, allows study of the time development of the NEIALs, though there are indications that even finer time resolution would be of interest. The analysis is based on the assumption that the NEIAL returns are the result of Bragg scattering from ion-acoustic waves that have been enhanced significantly above thermal levels. The spectra of the raw data indicate that although the up- and down-shifted shoulders can both become enhanced at the same time, (within 19 ms), they are most often enhanced individually. The overall power in the up-and down-shifted shoulders is approximately equal throughout the event, with the exception of one time, when very large up-shifted power was observed with no corresponding down-shifted power. This indicates that during the 480 μs pulse, the strongly enhanced ion-acoustic waves were only traveling downward and not upward. The exact time that the NEIALs occurred was when the radar beam was on the boundary of a fast-moving (~10 km/s), bright auroral structure, as seen in the high resolution auroral imaging of the magnetic zenith. When viewed with high time resolution, the occurrence of NEIALs is associated with rapid changes in auroral luminosity within the radar field of view due to fast-moving auroral fine structures.

Download Full-text

Stability of solitary kinetic Alfvén waves and ion-acoustic waves in a nonthermal plasma

Physics of Plasmas ◽

10.1063/1.874188 ◽

2000 ◽

Vol 7 (8) ◽

pp. 3227-3237 ◽

Cited By ~ 27

Author(s):

Anup Bandyopadhyay ◽

K. P. Das

Keyword(s):

Acoustic Waves ◽

Nonthermal Plasma ◽

Alfven Waves ◽

Alfvén Waves ◽

Ion Acoustic Waves ◽

Ion Acoustic ◽

Kinetic Alfvén Waves

Download Full-text

Stability and instability of some nonlinear dispersive solitary waves in higher dimension

Proceedings of the Royal Society of Edinburgh Section A Mathematics ◽

10.1017/s0308210500030614 ◽

1996 ◽

Vol 126 (1) ◽

pp. 89-112 ◽

Cited By ~ 21

Author(s):

Anne de Bouard

Keyword(s):

Solitary Waves ◽

Acoustic Waves ◽

Vries Equation ◽

Three Dimensional ◽

Higher Dimension ◽

Ion Acoustic Waves ◽

Stability And Instability ◽

Ion Acoustic ◽

De Vries ◽

The Stability

We study the stability of positive radially symmetric solitary waves for a three dimensional generalisation of the Korteweg de Vries equation, which describes nonlinear ion-acoustic waves in a magnetised plasma, and for a generalisation in dimension two of the Benjamin–Bona–Mahony equation.

Download Full-text