Implication of kilometre-scale fluctuations on the MGS radio-occultation-derived electron density profiles: artefacts or ionospheric wave-like structures

Abstract

ABSTRACT This study investigates the vertical kilometre-scale fluctuations (KSFs) seen on the Mars Global Surveyor (MGS) radio-occultation (RO)-derived electron density profiles (EDPs) by wavelet spectrum analysis. A delicate five-peak signature is revealed: in the northern polar region near the dawn–dusk terminator, the amplitudes of the KSF peak at fixed altitudes with a constant separation of approximately 28 km. The feature could not be noticed on a single EDP; averaging with at least tens of continuously collected EDPs is needed, suggesting that the phenomenon is not instantaneous (time duration of each RO event is ∼7 min), but on a time-scale of days (observation time for tens of continuous RO events). Applying similar background criteria, Mars Atmosphere and Volatile EvolutioN (MAVEN) Radio Occultation Science Experiment derived EDPs could also occasionally capture similar multipeak features, indicating either that it is a natural ionospheric structure or that both MGS and MAVEN suffer the same artefact. The two indications are discussed, and a preliminary hypothesis is raised. A linear superposition with a 28 km standing wave might modulate the amplitude of KSF, and the 28 km standing wave might be associated with the ionospheric buoyancy waves disturbed by the upstream solar wind, while the plasma instabilities might trigger the KSF in the backgrounds of the draped magnetic field and day-to-night neutral winds.