The Mars Magnetotail Current Sheet: ionospheric control of its systematic variation

Abstract:

Because Mars has no internal dipole magnetic field, the planetary magnetotail is created by draped interplanetary magnetic field. For a nominal Parker spiral IMF, the tail current sheet is aligned with the z axis, rather than the y axis as at Earth. The draping field is caused by the viscous interaction of the solar wind and IMF as they directly interact with the topside ionosphere. This study demonstrates, through analysis of magnetohydrodynamic simulation results, that there is a systematic asymmetry in the y location of the tail current sheet. For high solar flux conditions (i.e., solar maximum), the duskside magnetotail lobe is larger and the current sheet is offset in the –y (dawnward) direction. As with Venus, this configuration is caused by the azimuth angle of the IMF impacting the planet, allowing the field lines to remain in the lobe farther downtail on the duskside than on the dawnside. At solar minimum, the case is reversed, with the current sheet offset in the +y (duskward) direction. The weaker ionosphere at solar minimum allows for a deeper penetration of the magnetic pileup region on the dayside, increasing the viscous interaction and hampering IMF field line slippage past the planet. The s-shaped curvature of the magnetic field lines on the dawnside preferentially intensifies the field intensity of that lobe, shifting the location of the current sheet.