Articles | Volume 35, issue 4
Ann. Geophys., 35, 869–877, 2017
Ann. Geophys., 35, 869–877, 2017

Regular paper 26 Jul 2017

Regular paper | 26 Jul 2017

Quantification of the total ion transport in the near-Earth plasma sheet

Rikard Slapak1, Maria Hamrin2, Timo Pitkänen2, Masatoshi Yamauchi3, Hans Nilsson1,3, Tomas Karlsson4, and Audrey Schillings1,3 Rikard Slapak et al.
  • 1Division of Space Technology, Luleå University of Technology, Kiruna, Sweden
  • 2Department of Physics, Umeå University, Umeå, Sweden
  • 3Swedish Institute of Space Physics, Kiruna, Sweden
  • 4Space and Plasma Physics, School of Electrical Engineering, Royal Institute of Technology, Stockholm, Sweden

Abstract. Recent studies strongly suggest that a majority of the observed O+ cusp outflows will eventually escape into the solar wind, rather than be transported to the plasma sheet. Therefore, an investigation of plasma sheet flows will add to these studies and give a more complete picture of magnetospheric ion dynamics. Specifically, it will provide a greater understanding of atmospheric loss. We have used Cluster spacecraft 4 to quantify the H+ and O+ total transports in the near-Earth plasma sheet, using data covering 2001–2005. The results show that both H+ and O+ have earthward net fluxes of the orders of 1026 and 1024 s−1, respectively. The O+ plasma sheet return flux is 1 order of magnitude smaller than the O+ outflows observed in the cusps, strengthening the view that most ionospheric O+ outflows do escape. The H+ return flux is approximately the same as the ionospheric outflow, suggesting a stable budget of H+ in the magnetosphere. However, low-energy H+, not detectable by the ion spectrometer, is not considered in our study, leaving the complete magnetospheric H+ circulation an open question. Studying tailward flows separately reveals a total tailward O+ flux of about 0. 5 × 1025 s−1, which can be considered as a lower limit of the nightside auroral region O+ outflow. Lower velocity flows ( < 100 km s−1) contribute most to the total transports, whereas the high-velocity flows contribute very little, suggesting that bursty bulk flows are not dominant in plasma sheet mass transport.

Short summary
The ion total transports in the near-Earth plasma sheet have been investigated and quantified. Specifically, the net O+ transport is about 1024 s−1 in the earthward direction, which is 1 order of magnitude smaller than the typical O+ ionospheric outflows, strongly indicating that most outflow will eventually escape, leading to significant atmospheric loss. The study also shows that low-velocity flows (< 100 km s−1) dominate the mass transport in the near-Earth plasma sheet.