Influence of upstream solar wind on magnetic field distribution in the Martian nightside ionosphere

Using over eight years of Mars Atmosphere and Volatile EvolutioN (MAVEN) data, from November 2014 to May 2023, we have investigated the Martian nightside ionospheric magnetic field distribution under the influence of upstream solar wind drivers, including the interplanetary magnetic field intensity ( \left|\boldsymbolB_\mathrmI\mathrmM\mathrmF\right| ), solar wind dynamic pressure ( P_\mathrmS\mathrmW ), solar extreme ultraviolet flux (EUV), and Martian seasons ( L_\mathrms ). Our analysis reveals pronounced correlations between magnetic field residuals and both \left|\boldsymbolB_\mathrmI\mathrmM\mathrmF\right| and P_\mathrmS\mathrmW . Correlations observed with EUV flux and L_\rms were weaker — notably, magnetic field residuals increased during periods of high EUV flux and at Mars perihelion. We find that the IMF penetrates to an altitude of 200 km under a wide range of upstream conditions, penetrating notably deeper under high \left|\boldsymbolB_\mathrmIMF\right| and P_\mathrmSW conditions. Our analysis also indicates that EUV flux and IMF cone angle have minimal impact on IMF penetration depth. Those findings provide useful constraints on the dynamic nature of Martian atmospheric escape processes and their evolution, suggesting that historical solar wind conditions may have facilitated deeper IMF penetration and higher rates of ionospheric escape than are observed now. Moreover, by establishing criteria for magnetic ‘quiet’ conditions, this study offers new insights into the planet’s magnetic environment under varying solar wind influences, knowledge that should help refine models of the Martian crustal magnetic field.