A statistical study on O⁺ flux in the dayside magnetosheath

Abstract. Studies on terrestrial oxygen ion (O⁺) escape into the interplanetary space have considered a number of different escape paths. Recent observations however suggest a yet insufficiently investigated additional escape route for hot O⁺: along open magnetic field lines in the high altitude cusp and mantle. Here we present a statistical study on O⁺ flux in the high-latitude dayside magnetosheath. The O⁺ is generally seen relatively close to the magnetopause, consistent with observations of O⁺ flowing primarily tangentially to the magnetopause. We estimate the total escape flux in this region to be ~ 7 × 10²⁴ s⁻¹, implying this escape route to significantly contribute to the overall total O⁺ loss into interplanetary space.