Statistical Properties of Plateau‐Like Turbulence Spectra in the Martian Magnetosheath: MAVEN Observations

Abstract

AbstractThe 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 βi 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.