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The Electromagnetic Gradient Drift Instability: The Case of the Martian Ionosphere
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DOI：10.1029/2025JA034898.png)
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Abstract
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Electromagnetic instabilities in the collisional lower Martian ionosphere are investigated using a two-fluid model that incorporates collisional effects and density gradients. The model accounts for magnetization asymmetry between electrons and ions, where electrons remain magnetized while ions are strongly coupled to neutrals. A general dispersion relation is derived, capturing both real frequency and growth rate of unstable modes. Limiting-case analysis of the dispersion relation highlights the essential role of cross-field electron drift, collisional resistive coupling, and background density gradients as sources of free energy. The analysis identifies a hybrid electromagnetic instability that develops over intermediate perpendicular wavelengths, driven by gradient-drift processes but modulated by magnetic-pressure and collisional dissipation. Numerical solutions reveal distinct parametric regimes controlled by ion-neutral and electron-neutral collisionalities, magnetic-pressure, and density gradient strength. Growth rates exhibit well-defined unstable windows in both wavenumber and parameter space, with optimal instability occurring at moderate ion collisionality and low-to-moderate electron collisionality. The model explains the key physical mechanisms responsible for small-scale plasma irregularities observed by MAVEN at altitudes below 200 km, providing a theoretical framework for interpreting electromagnetic fluctuations in the weakly ionized Martian ionosphere.
Keywords:
Martian ionosphere
electromagnetic instabilities
gradient-drift instability
two-fluid plasma model
collisional ionosphere
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2.9
Papers:
268
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0
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