O<sup>+</sup> transport in the dayside magnetosheath and its dependence on the IMF direction

Abstract

Abstract. Recent studies have shown that the escape of oxygen ions (O + ) into the magnetosheath along open magnetic field lines from the terrestrial cusp and mantle is significant. We present a study of how O + transport in the dayside magnetosheath depends on the interplanetary magnetic field (IMF) direction. There are clear asymmetries in the O + flows for southward and northward IMF. The asymmetries can be understood in terms of the different magnetic topologies that arise due to differences in the location of the reconnection site, which depends on the IMF direction. During southward IMF, most of the observed magnetosheath O + is transported downstream. In contrast, for northward IMF we observe O + flowing both downstream and equatorward towards the opposite hemisphere. We observe evidence of dual-lobe reconnection occasionally taking place during strong northward IMF conditions, a mechanism that may trap O + and bring it back into the magnetosphere. Its effect on the overall escape is however small: we estimate the upper limit of trapped O + to be 5 %, a small number considering that ion flux calculations are rough estimates. The total O + escape flux is higher by about a factor of 2 during times of southward IMF, in agreement with earlier studies of O + cusp outflow.

Atmospheric loss from the dayside open polar region and its dependence on geomagnetic activity: implications for atmospheric escape on evolutionary timescales

“…The data set used for the plasma mantle statistics was obtained by SC4 andcovers 2001-2005. For the high-latitude magnetosheath we use the data set compiled by Slapak et al (2013), in which times of high-energy O + were visually determined for 2001-2003 for SC1.…”

“…O + data in the high-latitude dayside magnetosheath covering 2001 to 2003 were identified by Slapak et al (2013) through the visual inspection of O + energy spectrograms for ion energies larger than 3 keV in order to avoid false counts due to the intense H + fluxes in the magnetosheath (Nilsson et al, 2006). The middle panel of Fig.…”

“…1) depending on how effectively it is accelerated: (1) low-energised ion populations will convect anti-sunward across the polar cap and further downtail and towards the plasma sheet, where they end up on closed field lines Liao et al, 2015); (2) sufficiently energised ions will reach the plasma mantle with typical velocities high enough to pass the tail X-line and consequently escape in the distant tail ; (3) highly energised ions may escape into the dayside magnetosheath directly from the cusps (Slapak et al, , 2013. Heavy (e.g.…”

“…Escaping ions during a strong northward interplanetary magnetic field may be brought back into the magnetosphere if dual-lobe reconnection takes place (Song and Russell, 1992). The fraction that might be brought back is, however, a low percentage and its effect on the total escape along route 3 is negligible (Slapak et al, 2015).…”

Energy conversion through mass loading of escaping ionospheric ions for different Kp values

“…However, ion data from Cluster and Polar have revealed that a large amount of ionospheric ions are kept supplied to the exterior cusp, plasma mantle and magnetosheath, with a total flux of about 10 24−26 s −1 (Peterson et al, 2008;Slapak et al, 2013Slapak et al, , 2015 and with a local number density ratio to the solar wind of about 1 %. This amount is sufficient to substantially decelerate the solar wind by about 10 % because of 16 times heavier mass of O + than H + , and might significantly influence the electrodynamics of the polar ionosphere, e.g.…”