Articles | Volume 35, issue 3
Ann. Geophys., 35, 721–731, 2017
Ann. Geophys., 35, 721–731, 2017

Regular paper 12 Jun 2017

Regular paper | 12 Jun 2017

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

Rikard Slapak1, Audrey Schillings1,2, Hans Nilsson1,2, Masatoshi Yamauchi2, Lars-Göran Westerberg3, and Iannis Dandouras4,5 Rikard Slapak et al.
  • 1Division of Space Technology, Luleå University of Technology, Kiruna, Sweden
  • 2Swedish Institute of Space Physics, Kiruna, Sweden
  • 3Division of Fluid and Experimental Mechanics, Luleå University of Technology, Luleå, Sweden
  • 4CNRS, Institut de Recherche en Astrophysique et Planétologie, Toulouse, France
  • 5University of Toulouse, UPS-OMP, IRAP, Toulouse, France

Abstract. We have investigated the total O+ escape rate from the dayside open polar region and its dependence on geomagnetic activity, specifically Kp. Two different escape routes of magnetospheric plasma into the solar wind, the plasma mantle, and the high-latitude dayside magnetosheath have been investigated separately. The flux of O+ in the plasma mantle is sufficiently fast to subsequently escape further down the magnetotail passing the neutral point, and it is nearly 3 times larger than that in the dayside magnetosheath. The contribution from the plasma mantle route is estimated as  ∼ 3. 9 × 1024exp(0. 45 Kp) [s−1] with a 1 to 2 order of magnitude range for a given geomagnetic activity condition. The extrapolation of this result, including escape via the dayside magnetosheath, indicates an average O+ escape of 3 × 1026 s−1 for the most extreme geomagnetic storms. Assuming that the range is mainly caused by the solar EUV level, which was also larger in the past, the average O+ escape could have reached 1027–28 s−1 a few billion years ago. Integration over time suggests a total oxygen escape from ancient times until the present roughly equal to the atmospheric oxygen content today.

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Short summary
In this study, we have used Cluster satellite data to quantify the ionospheric oxygen ion (O+) escape into the solar wind and its dependence on geomagnetic activity. During times of high activity, the escape may be 2 orders of magnitude higher than under quiet conditions, strongly suggesting that the escape rate was much higher when the Sun was young. The results are important for future studies regarding atmospheric loss over geological timescales.