Observations of oxygen ions in the dayside magnetosheath associated with southward IMF

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

“…2 shows such typical magnetosheath high-energy O + populations (marked with red rectangles) in the interval up to the magnetopause crossing at ∼ 09:18. Studies of such populations were presented by Slapak et al (2012), who reported that the pop- ulations had D-shaped velocity distributions, indicating that they had passed through a rotational discontinuity at the magnetopause, which is consistent with escape along open field lines. Only the months January to June were considered when picking out these types of magnetosheath O + populations as this period corresponds to a Cluster apogee in the dayside, allowing for regular passages through the high-latitude dayside magnetosheath.…”

A statistical study on O<sup>+</sup> flux in the dayside magnetosheath

“…The reason for a lower energy limit is to avoid contamination of the O + data when intense proton fluxes are present. From inspection it is clear that significantly heated and accelerated O + ions reach particle energies up to at least 38 keV (the maximum energy per charge to be measured by CODIF), whereas the magnetosheath protons seldom reach energies above 3 keV; see, e.g., the case study presented by Slapak et al (2012). Therefore, an O + set containing ions of energies > 3 keV is assumably unaffected by the intense proton fluxes, whereas a low energy subset (< 3 keV) is strongly contaminated.…”

“…The escape does not necessarily have to take place in the distant magnetotail after passing the neutral point, but may flow across the magnetopause into the magnetosheath along open field lines. A case study of O + in the dayside magnetosheath was presented by Slapak et al (2012). They concluded that the ions had escaped along open magnetic field lines directly from the cusp/mantle, and they showed that this escape route is possible if the upflowing ions are heated sufficiently in the cusps.…”

“…They estimated the total O + loss rate (including escape in the tail lobes, via plasmoids, and leakage of plasma sheet and ring-current ions through the dayside magnetopause) to be ∼ 5 ×10 24 s −1 . However, they did not consider direct O + escape along open magnetic field lines from the cusp/mantle into interplanetary space, which the studies of Slapak et al (2012) and Nilsson et al (2012) indicate can be significant and therefore worth investigating. Studies of polar cap/cusp O + flows have been performed by several authors (Abe et al, 1996;Yau and André, 1997;Lennartsson et al, 2004;) who all estimated a total outflow flux of the order ∼ 10 25 s −1 .…”

O&lt;sup&gt;+&lt;/sup&gt; transport in the dayside magnetosheath and its dependence on the IMF direction

“…Observations of O + in the dayside magnetosheath have been reported many times; see, e.g. Zong et al (2001), Marcucci et al (2004), Kasahara et al (2008) and Slapak et al (2012). A statistical study of O + in the high-latitude dayside magnetosheath was made by Slapak et al (2013), showing that O + is common, contributing 0.7 × 10 25 s −1 to the total O + escape flux.…”