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Volume 27, issue 2
Ann. Geophys., 27, 839–849, 2009
https://doi.org/10.5194/angeo-27-839-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 27, 839–849, 2009
https://doi.org/10.5194/angeo-27-839-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.

  19 Feb 2009

19 Feb 2009

Outflowing protons and heavy ions as a source for the sub-keV ring current

T. T. Giang1, M. Hamrin2, M. Yamauchi1, R. Lundin1, H. Nilsson1, Y. Ebihara3, H. Rème4, I. Dandouras4, C. Vallat5, M. B. Bavassano-Cattaneo6, B. Klecker7, A. Korth8, L. M. Kistler9, and M. McCarthy10 T. T. Giang et al.
  • 1Swedish Institute of Space Physics, Kiruna, Sweden
  • 2Department of Physics, Umeå University, Umeå, Sweden
  • 3Institute for Advanced Research, Nagoya University, Japan
  • 4Centre d'Etude Spatiale des Rayonnements, Toulouse, France
  • 5VEGA contracted to Solar System Science Operations Division, ESA/ESAC, Madrid, Spain
  • 6L'Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
  • 7Max Planck Institute for Extraterrestrial Physics, Garching, Germany
  • 8Max-Planck-Institut für Sonnensystemforschung, Katlenburg-Lindau, Germany
  • 9University of New Hampshire, Durham, New Hampshire, USA
  • 10University of Washington, Seattle, USA

Abstract. Data from the Cluster CIS instrument have been used for studying proton and heavy ion (O+ and He+) characteristics of the sub-keV ring current. Thirteen events with dispersed heavy ions (O+ and He+) were identified out of two years (2001 and 2002) of Cluster data. All events took place during rather geomagnetically quiet periods. Three of those events have been investigated in detail: 21 August 2001, 26 November 2001 and 20 February 2002. These events were chosen from varying magnetic local times (MLT), and they showed different characteristics.

In this article, we discuss the potential source for sub-keV ring current ions. We show that: (1) outflows of terrestrial sub-keV ions are supplied to the ring current also during quiet geomagnetic conditions; (2) the composition of the outflow implies an origin that covers an altitude interval from the low-altitude ionosphere to the plasmasphere, and (3) terrestrial ions are moving upward along magnetic field lines, at times forming narrow collimated beams, but frequently also as broad beams. Over time, the ion beams are expected to gradually become isotropised as a result of wave-particle interaction, eventually taking the form of isotropic drifting sub-keV ion signatures. We argue that the sub-keV energy-time dispersed signatures originate from field-aligned terrestrial ion energising and outflow, which may occur at all local times and persist also during quiet times.

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