Statistical Properties of Plateau‐Like Turbulence Spectra in the Martian Magnetosheath: MAVEN Observations. Issue 1 (9th January 2023)

• Record Type: Journal Article
• Authors: Jiang, Wence; Li, Hui; Liu, Xiaodong; Verscharen, Daniel; Wang, Chi
• Is Part Of: Journal of geophysical research. Volume 128:Issue 1(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-01-09
• Subjects: Mars -- magnetosheath -- MHD turbulence -- pick‐up ions -- proton cyclotron waves; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA030874
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: The Martian magnetosheath provides us with a natural laboratory to study plasma turbulence in the presence of pickup ions and locally generated instabilities. Unlike the typical magnetic‐field spectra with a single spectral scaling at magnetohydrodynamics (MHD) scales in Earth's magnetosheath, the magnetic‐field spectra in the Martian magnetosheath during 4 years of Mars Atmosphere and Volatile EvolutioN observations frequently present an additional spectral break‐point with a shallow slope at MHD scales which we define as a plateau‐like spectral feature. The average occurrence rate of plateau‐like magnetic‐field spectra is 56.6% of our measurement intervals. At moderate pick‐up angles, the occurrence rate increases to a maximum of ∼70.0%. Furthermore, we present a positive correlation with the local ion density and anti‐correlations with the local β i and the solar Extreme Ultra Violet irradiance. A similar occurrence rate in the quasi‐perpendicular and the quasi‐parallel magnetosheath (60.1% vs. 52.9%) indicates that the plateau‐like spectra are more likely formed locally than in the upstream solar wind. Our results suggest that energy injection from pickup ion driven micro‐instabilities, for example, in the form of proton cyclotron waves, has insufficient time to evolve into a fully developed cascade in such a confined space like the Martian magnetosheath. Plain Language Summary: Magnetic‐field turbulence is ubiquitous in planetary plasma environments. However, our current understanding of turbulence injection and dissipation in the magnetosheath is still very limited. At Mars, the far‐extended neutral exospheres of hydrogen and oxygen provide an extraordinary environment to study the energy injection into the background turbulence by pickup ions. Our statistical study reveals that a large fraction of the observed magnetic‐field spectra exhibit a triple power‐law with a broadband plateau‐like feature. We quantify the occurrence of plateau‐like spectra and correlate it with pickup‐ion‐related parameters. We find that strong energy injection driven by pickup ions, including but not limited to proton cyclotron waves, creates these plateaus. The generated waves cannot evolve into a fully developed cascade given the insufficient spatial extent of the Martian magnetosheath. Key Points: Plateau‐like magnetic‐field spectra with triple power laws are ubiquitous in the Martian magnetosheath Comprehensive statistical results suggest strong correlations between the plateau occurrence rate and pickup ion related parameters The formation of plateau‐like spectra is possibly due to energy injections from waves driven by pickup ions from Mars