Abstract | The magnetic field topology surrounding the Martian atmosphere is mainly the result of gradients in the velocity of
the solar wind (SW). Such variations in the SW velocity are in turn the result of a massloading process and forces
associated with electric currents flowing around the ionosphere of Mars [Nagy et al 2004, Mazelle et al 2004,
Brain et al 2015]. In particular, in the regions where the collisionless regime holds, the interplanetary magnetic
field (IMF) frozen into the SW piles up in front of the stagnation region of the flow. At the same time, the magnetic
field lines are stretched in the direction of the unperturbed SW as this stream moves away from Mars, giving rise
to a magnetotail [Alfvén, 1957]. As a result and in contrast with an obstacle with and intrinsic global magnetic
field, the structure and organization of the magnetic field around Mars depends on the direction of the IMF and its
variabilities [Yeroshenko et al., 1990; Crider et al., 2004; Bertucci et al., 2003; Romanelli et al 2015].
In this study we use magnetometer data from the Mars Global Surveyor (MGS) spacecraft during portions of the
premapping orbits of the mission to study the variability of the Martian-induced magnetotail as a function of the
orientation of the IMF. The time spent by MGS in the magnetotail lobes during periods with positive solar wind
flow-aligned IMF component BIMF// suggests that their location as well as the position of the central polarity reversal
layer (PRL) are displaced in the direction antiparallel to the IMF cross-flow component BIMFperp . Analogously,
in the cases where BIMF// is negative, the lobes are displaced in the direction of BIMFperp . We find this behavior to be
compatible with a previously published BIMFperp analytical model of the IMF draping, where for the first time, the
displacement of a complementary reversal layer (denoted as IPRL for inverse polarity reversal layer) is deduced
from first principles [Romanelli et al 2014]. We also analyzed these results in the context of recent observations
provided by the Mars Atmospheric and Volatile Evolution spacecraft [e.g. DiBraccio et al 2015]. |
