Lecturer: Sachiko Arvelius (IRF)
Date: 2008-12-04 10:30
Place: Aniara

Statistical budgets of oxygen (O+) and hydrogen (H+) between Earth and the space: Implications in terms of magnetospheric physics and planetary chemical evolution

Sachiko Arvelius
Swedish Institute of Space Physics

We first time derived statistical budgets of non-thermal O+ and H+ between Earth and the space, i.e. across/through a complete spherical shell at R=5 Earth radii (Re) geocentric distance, from direct measurement. We used four-year Cluster satellites' ion data since 2001 to 2004. On average, more than 80% of outflowing O+ across 5 Re are returning to Earth. Resulting net escape on average across 5 Re of 0.6 kg/s (2.2*1025 ions/s) for O+, and 0.2 kg/s (10.9*1025 ions/s) for H+. The O/H number ratio of net escape on average is much less (1:5) than 1:2 which is referred as the stoichiometric ratio corresponding to water (H2O). This value can be compared to which is derived for Venus (e.g., Barabash et al.(2007)) in terms of planetary chemical evolution. On the other hand, the O/H ratio of net escape emerged from Earth also (and very much) depends on the geomagnetic activity which affects drastically O+ inflow through 5 Re. Our study shows that (1) amount of O+ inflow through 5 Re which is comparable to O+ outflow across 5 Re is a real and this indicates the order and (spatial) distribution of O+ return flow suggested by Seki et al.(2001) (and indirect measurement), and (2) the history of O/H ratio of net escape when we use Kp-index as a proxy of solar wind variabilities.

Created 2008-09-12 09:51:00 by Mats Holmström
Last changed 2008-12-01 10:28:29 by Mats Holmström