Distribution of the Ring Current and Coupling with Field-Aligned Currents: Joint observation of MMS and Swarm

Abstract

<p>The ring current and field-aligned currents have a dominant effect in the inner magnetospheric current system, where the coupling mechanism to the ionosphere has a significant impact on space weather and magnetic activity on the ground. We use FGM data from the four spacecraft MMS mission to estimate <em>in situ</em> current density and study the distribution of the ring current, by statistically analyzing the azimuth component of current density. We also compare the statistical results of field-aligned component of current density from MMS with the statistical results of dual-FAC data of Swarm in the same time range to explore the large-scale coupling of the ring current and field-aligned currents. The joint observational results show that: on the one hand (on the dawn side), due to the injection of Region 2 field-aligned currents, the westward ring current increases continuously from noon to midnight; while (on the dusk side, from midnight to noon), due to the injection of Region 1 field-aligned current near midnight and the outflow of Region 2 field-aligned currents, the westward ring current increases, then decreases until it turns eastward and increases in magnitude. On the other hand, due to the existence of a mesoscale, clockwise banana current centered at about 4.8Re (Earth Radii) between noon and dusk, the eastward ring current is significantly enhanced in the inner ring and enhanced westward in the outer ring. Similarly, due to the existence of a mesoscale counterclockwise current centered at about 4.8Re between midnight and dawn, the westward ring current is slightly enhanced in the inner ring and enhanced eastward in the outer ring. The influence of these two factors on the distribution of the ring current is of the same order of magnitude. Work to clarify the operation of these effects relative to activity levels is in progress.</p>