Magnetic field disturbances in the martian ionosphere: Competing roles of ionospheric currents and solar wind interaction

Abstract

We examine disturbances in the total magnetic field in the Martian ionosphere at altitudes of 150–1,000 km and investigate their potential sources, focusing on ionospheric density variations and solar wind dynamic pressure (Psw) using Mars Atmosphere and Volatile Evolution spacecraft measurements. Disturbances in the magnetic field and ion densities were derived using a Savitzky–Golay filter. Our results reveal a clear dawn–dusk asymmetry in disturbances in the magnetic field and O2+ density at lower altitudes (150–200 km), with perturbations being stronger on the dawn side. Correlation analysis indicates that disturbances in the magnetic field show a moderately significant correlation with disturbances in O2+ density at these altitudes, where O2+ is the dominant ion, whereas disturbances in O+ density exhibit the highest correlation with magnetic field disturbances near 250–300 km, coinciding with its density maximum. These results suggest that ionospheric plasma variations contribute to magnetic field variability in the lower ionosphere. At higher altitudes (>400 km), the correlation between disturbances in the magnetic field and ion densities decreases with altitude, while the relationship between disturbances in the magnetic field and Psw gradually increases, particularly above ∼600 km. Crustal magnetic anomalies also influence the spatial distribution of disturbances: at lower altitudes they enhance the correlation between magnetic field and ion density disturbances, whereas at higher altitudes disturbances are relatively stronger in non-anomaly regions, likely due to direct solar wind interaction. These results highlight the altitude-dependent contributions of ionospheric plasma processes and solar wind forcing to magnetic field disturbances in the Martian ionosphere.