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  Steepening of magnetosonic waves in the inner coma of comet 67P/Churyumov-Gerasimenko

Ostaszewski, K., Glassmeier, K.-H., Goetz, C., Heinisch, P., Henri, P., Park, S., et al. (2021). Steepening of magnetosonic waves in the inner coma of comet 67P/Churyumov-Gerasimenko. Annales Geophysicae, 39(4), 721-742. doi:10.5194/angeo-39-721-2021.

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Ostaszewski, K., Author
Glassmeier, Karl-Heinz1, Author              
Goetz, C., Author
Heinisch, P., Author
Henri, P., Author
Park, S.A., Author
Ranocha, H., Author
Richter, I., Author
Rubin, M., Author
Tsurutani, B., Author
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1Max Planck Institute for Solar System Research, Max Planck Society, ou_1125546              

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 Abstract: We present a statistical survey of large-amplitude, asymmetric plasma and magnetic field enhancements detected outside the diamagnetic cavity at comet 67P/Churyumov–Gerasimenko from December 2014 to June 2016. Based on the concurrent observations of plasma and magnetic field enhancements, we interpret them to be magnetosonic waves. The aim is to provide a general overview of these waves' properties over the mission duration. As the first mission of its kind, the ESA Rosetta mission was able to study the plasma properties of the inner coma for a prolonged time and during different stages of activity. This enables us to study the temporal evolution of these waves and their characteristics. In total, we identified ∼ 70 000 steepened waves in the magnetic field data by means of machine learning. We observe that the occurrence of these steepened waves is linked to the activity of the comet, where steepened waves are primarily observed at high outgassing rates. No clear indications of a relationship between the occurrence rate and solar wind conditions were found. The waves are found to propagate predominantly perpendicular to the background magnetic field, which indicates their compressional nature. Characteristics like amplitude, skewness, and width of the waves were extracted by fitting a skew normal distribution to the magnetic field magnitude of individual steepened waves. With increasing mass loading, the average amplitude of the waves decreases, while the skewness increases. Using a modified 1D magnetohydrodynamic (MHD) model, we investigated if the waves can be described by the combination of nonlinear and dissipative effects. By combining the model with observations of amplitude, width and skewness, we obtain an estimate of the effective plasma diffusivity in the comet–solar wind interaction region and compare it with suitable reference values as a consistency check. At 67P/Churyumov–Gerasimenko, these steepened waves are of particular importance as they dominate the innermost interaction region for intermediate to high activity.

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Language(s): eng - English
 Dates: 2021
 Publication Status: Published in print
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 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.5194/angeo-39-721-2021
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Title: Annales Geophysicae
Source Genre: Journal
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Publ. Info: Montrouge Cedex, France : Gauthier-Villars
Pages: - Volume / Issue: 39 (4) Sequence Number: - Start / End Page: 721 - 742 Identifier: ISSN: 0992-7689
CoNE: https://pure.mpg.de/cone/journals/resource/954928606127