Spatial Scales of Electron Density Fluctuations in the Martian Ionosphere

Abstract In recent Martian ionospheric studies, the spatial scales of electron density irregularities have been computed using magnetic field measurements by treating these fluctuations as electromagnetic. As Mars lacks an intrinsic magnetic field, estimation of spatial scales in the parallel and perpendicular directions of the ambient magnetic field is not straightforward. In the present study, the magnetic field averaged over a longer time window is used to get the direction of the ambient magnetic field. The process of averaging removes the short-time fluctuations and retains only the slowly varying part, which can be treated as an ambient magnetic field. This approach is applied to long-term (2014–2023) magnetic field measurements from the fluxgate magnetometer on board the Mars Atmosphere and Volatile EvolutioN (or MAVEN) spacecraft to investigate separately the dominant spatial scales in the parallel and perpendicular directions. The spatial scales parallel and perpendicular to the ambient magnetic field dominantly lie in the range of λ ∣∣ = 150–350 km and λ ⊥= 50–80 km, respectively. However, the tendency of λ ∣∣ > λ ⊥ weakens in the region of the strong crustal magnetic field. Irregularities with density fluctuations of more than 25% are prevalent in the dawn and dusk sectors at an altitude of 140–180 km. Spatial scales of λ ⊥ < 70 km are more probable at an altitude above 200 km in the Martian ionosphere. Information about the spatial scales of electron density fluctuations is crucial for understanding their impact on the radio wave propagation in the Martian ionosphere, as well as the underlying processes responsible for their generation.