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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 22, issue 12
Ann. Geophys., 22, 4229–4241, 2004
https://doi.org/10.5194/angeo-22-4229-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 22, 4229–4241, 2004
https://doi.org/10.5194/angeo-22-4229-2004
© Author(s) 2004. This work is distributed under
the Creative Commons Attribution 3.0 License.

  22 Dec 2004

22 Dec 2004

A statistical study of unstable particle populations in the global ringcurrent and their relation to the generation of high m ULF waves

L. J. Baddeley1, T. K. Yeoman1, D. M. Wright1, K. J. Trattner2, and B. J. Kellet3 L. J. Baddeley et al.
  • 1Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
  • 2Lockheed Martin ATC, Palo Alto, USA
  • 3Rutherford Appleton Laboratory, Didcot, UK

Abstract. The first statistical study of the unstable proton populations which contain "free energy" required to drive small-scale poloidal mode ULF waves in the magnetosphere between L-shell locations of 6 and 9 is presented. The data examined are all in the form of Ion Distribution Functions (IDFs) covering a particle energy range of 0.025keV to 328keV, amassed over 2.5 years from the TIMAS and CAMMICE (MICS) instruments on-board the Polar spacecraft. Any free energy which is available to drive a resonant wave mode manifests itself as a positive gradient region in the IDF. A new analysis technique applied to the data, allows for the first time, the amount of free energy contained in each IDF to be quantified. The results show that IDFs are a common occurrence in the magnetosphere at these L-shells, although they are most common in the dawn/pre-noon sector. Lower energy (10–45keV) protons are the most commonly observed unstable populations and also contain the largest amounts of free energy (>1010J). Positive gradient regions at higher energies (>100keV) are rarely observed and also contain greatly reduced free energies (<109J).

Key words. Magnetospheric physics (Energetic particles, trapped; MHD waves and instabilities) – Space plasma physics (wave-particle interactions)

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