Dayside ionospheric conductivities and horizontal currents derived from MAVEN/ROSE data

Abstract

A complex magnetic topology at Mars gives rise to diverging magnetic field cusps and closed magnetic loops with local magnetic conditions similar to those found above Earth’s polar region. Several such cusps are identified from MAVEN/Radio Occultation Science Experiment (ROSE) electron density profiles mostly observed during the period July 2016 to December 2020 in the southern high latitudes, where the crustal magnetic field is nearly vertical and open to the access of solar wind plasma through magnetic reconnection with the interplanetary magnetic field.  This reconnection can allow solar wind electrons to penetrate the Martian upper atmosphere, causing ionization and heating, which leads to inflate the topside plasma distribution to high altitude and increase the topside electron density scale heights. We use our 1-D chemical diffusive model from an altitude of 100 km to 400 km to interpret the twenty ROSE electron density profiles with the vertical plasma transport simulated by vertical ion velocities and by imposing an outward flux boundary condition.  The output of this model and available crustal magnetic field information at Mars are used to estimate the vertical distribution of ionospheric conductivities.  We find that the ionosphere is highly conductive in the Martian dynamo region between 100 and 220 km altitude where plasma –neutral collisions permit electric currents perpendicular to the crustal magnetic field.  The magnitudes of Pedersen and Hall conductivities are estimated to be ~0.60 – 0.85 S/m, respectively, near the Martian ionospheric peak of the observed electron density profiles included in this study. The electrons in this region are constrained to gyrate along magnetic field lines while ions are dragged by neutrals and move along the direction of applied force. In the absence of the electric field, the horizontal current in the Martian dynamo is generated by the differential motion of ions and electrons. The results of the present study will allow us to quantify the flow of atmospheric electric currents which can be analyzed for a deeper understanding of the Martian ionospheric electrodynamics. The model results will be presented in comparison with existing estimates of the Martian conductivities and ionospheric currents.