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

L. J. Baddeley (1) , T. K. Yeoman (1) , D. M. Wright (1) , K. J. Trattner (2) , B. J. Kellet (3)

1 Department of Physics and Astronomy [Leicester]
2 ATL - Lockheed Martin Advanced Technology Laboratories
3 RAL - STFC Rutherford Appleton Laboratory

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)

Domaines: Océan, Atmosphère; Sciences de la Terre

L. J. Baddeley, T. K. Yeoman, D. M. Wright, K. J. Trattner, B. J. Kellet. A statistical study of unstable particle populations in the global ringcurrent and their relation to the generation of high m ULF waves. Annales Geophysicae, 2004, 22 (12), pp.4229-4241. ⟨hal-00317788⟩