Abstract
Using over 6 years of magnetic field data (2014.10-2020.12) collected by
the Mars Atmosphere and Volatile EvolutioN (MAVEN), we conduct a
statistical study on the three-dimensional average magnetic field
structure around Mars. We find that this magnetic field structure
conforms to the pattern typical of an induced magnetosphere, that is,
the interplanetary magnetic field (IMF) which is carried by the solar
wind and which drapes, piles up, slips around the planet, and eventually
forms a tail in the wake. The draped field lines from both hemispheres
along the direction of the solar wind electric field (E) are directed
towards the nightside magnetic equatorial plane, which looks like they
are “sinking” toward the wake. These “sinking” field lines from the
+E-hemisphere (E pointing away from the plane) are more flared and
dominant in the tail, while the field lines from the –E-hemisphere (E
pointing towards) are more stretched and “pinched” towards the plasma
sheet. Such highly “pinched” field lines even form a loop over the
pole of the –E-hemisphere. The tail current sheet also shows an
E-asymmetry: the sheet is thicker with a stronger tailward J×B force at
+E-flank, but much thinner and with a weaker J×B (even turns sunward) at
–E-flank. Additionally, we find that IMF Bx can induce
a kink-like field structure at the boundary layer; the field strength is
globally enhanced and the field lines flare less during high dynamic
pressure; however, the rotation of the planet, against expectations,
modulate the configuration of the tail current sheet insignificantly.