Case studies of the dynamics of ionospheric ions in the Earth's magnetotail

• Published in: Journal of Geophysical Research. A. Space Physics 2004-01, Vol.109 (A1), p.A01212.1-n/a
• Main Authors: Sauvaud, J.-A., Louarn, P., Fruit, G., Stenuit, H., Vallat, C., Dandouras, J., Rème, H., André, M., Balogh, A., Dunlop, M., Kistler, L., Möbius, E., Mouikis, C., Klecker, B., Parks, G. K., McFadden, J., Carlson, C., Marcucci, F., Pallocchia, G., Lundin, R., Korth, A., McCarthy, M.
• Format: Article
• Language: English
• Subjects: Alfven waves; Earth, ocean, space; Exact sciences and technology; External geophysics; injections; magnetotail; oxygen; Physics of the high neutral atmosphere; Physics of the ionosphere; Physics of the magnetosphere; substorms; terrestrial ions
• ISSN: 0148-0227; 2156-2202
• DOI: 10.1029/2003JA009996

This paper presents case studies of the dynamics of the terrestrial ions in the midplasma sheet and inside the lobes (∼17–19 RE). The high time resolution measurements of H+, He+, and O+ ions made on board Cluster show that these ions are massively injected into the tail during substorms/storms from the nightside ionosphere and mainly dispersed by time of flight effects; a single oxygen injection being able to account for over 80% of the oxygen population of the midtail plasma sheet during storm time. Inside the lobes, during disturbed times, ionospheric oxygen ions appear as nearly monoenergetic beams, quasi field‐aligned, propagating antisunward from the ionosphere, as expected from the “cleft ion fountain.” Most of the time, the ionospheric protons are very cold and their distribution function is not fully measurable by a charged spacecraft. However, we show that protons can, at times, acquire a large drift motion, reach energy larger than 30 eV, and be directly measurable by the CIS spectrometers. This occurs when large disturbances propagate in the plasma sheet boundary layer during both quiet and disturbed periods. We show that the large, variable, Alfvén waves generated by these plasma sheet disturbances modulate the energy of lobe protons and oxygen ions and inject electromagnetic energy, in excess of 15 × 10−3 W/m2, down to the polar cap. Deeper inside the plasma sheet boundary layer, large electric fields associated with the Earthward stream of plasma sheet particles give enough drift energy to a very cold ionospheric proton population to become fully detectable by the Cluster ion spectrometers.