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Cluster observation of electron acceleration by ULF Alfvén waves

Cluster observation of electron acceleration by ULF Alfvén waves. Above the auroral region at altitude of 5-6Re, periodic upward (sometimes downward) electron beams are often observed by CLUSTER. They are coincide with ULF Alfvén waves (E- and B- field disturbance) of few minutes.

mohammad-jennings
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Cluster observation of electron acceleration by ULF Alfvén waves

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  1. Cluster observation ofelectron accelerationby ULF Alfvén waves • Above the auroral region at altitude of 5-6Re, periodic upward (sometimes downward) electron beams are often observed by CLUSTER. • They are coincide with ULF Alfvén waves (E- and B- field disturbance) of few minutes. • The coexistence of the beams and the ULF waves implies their close relationship. OUTLINE • CLUSTER observation above the nightside auroral region • High latitude (~70˚-80˚) • Altitudes: 5-6 RE • Periodic upward electron flux structures • Electric/Magnetic field disturbances at similar period • DMSP conjunction observation • Temporal/Spatial signatures by four S/C observations • E/B ratio: Signatures of Alfvén waves • Downward Poynting flux comparable to electron’s energy • Electron acceleration signatures shows time viabilities. • Wave forms do not look like structure. • Vortex structure.

  2. CLUSTER-II 2002-04-15 summary • electrons • Up • Perp. • Down B-field E-field dB Poynting Flux ∑S ~300 km

  3. Conjunction betweenDMSP-CLUSTER DMSP SSM CLUSTER FGM

  4. E/B ratio : 106 [m/s] (0.8 mho) • ≈ Alfvén speed : ≈106 [m/s] • ≤ Pedersen conductivity (~few mho is expected.)

  5. Electron signatures 21:53:30 21:54:15 S/C-1 S/C-2 S/C-3 S/C-4 21:55:30

  6. Up Down EFW Epole Beast FGM S ∑S

  7. ?

  8. ? B E

  9. ? B E

  10. ? B E

  11. summary About 2 minutes oscillation of electron loss corn/upward electron beam and E-field, B-field have been observed at the plasmasheet boundary above the auroral region. They are coincide with … Upward field aligned current region Upward ion beam region. E-, B- field disturbances are likely to be Alfvén waves, and the electrons are accelerated directly by the Alfvén waves. • E/B ratio: Signatures of Alfvén waves • Downward Poynting flux comparable to electron’s energy • Electron acceleration signatures shows time viabilities. • Wave forms do not look like structure. • Several hundreds km of perpendicular wave length. • Vortex structure.

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