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. 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. Above the dayside high latitude at altitude of 5-6Re, the Cluster satellite often observes upward electron beams with periodic structures in wide region. Magnetic/Electric disturbances with few minutes associated to the electron beams, and they are expected to relate to the energyzation mechanisms. Four Cluster spacecraft observation indicates that there are finite (1~2o iLat) structures. However, the electric/magnetic field disturbances have periodic structures with characteristics of Alfvén waves, and show time variability. Poynting Flux indicates that the wave energy propagate toward the Earth and has energy comparable to the electron’s energy flux. Since magnetic field often shows vortex like signatures, we expect that the generation region of the small scale structures is related to the surface wave activity in the boundary region. Abstract. Upgoing electron beams have been often associated with low frequency electric fields at the pole ward of Plasmasheet boundary region with low-altitudes (up to 2Re) spacecrafts [e.g. Hulqvist et al., 1991]. Above the dayside auroral region at altitude of 5-6Re, the Cluster satellite also observes upward (sometimes downward) electron beams and they are associated with ULF Alfvén waves of few minutes. The coexistence of the beams and the ULF waves implies their close relationship. The pitch angle distributions of the electrons also suggest that the electrons are accelerated by the Alfvén waves. Alfvén waves from the nightside Plasmasheet boundary layer is discussed recently, in connection with the substorm onset or magnetic reconnection, and proposed as the main source energy of the auroral processes [e.g. Kieling et al., 2003]. Such ULF wave observations are similar in many ways to the events observed on the dayside. On the dayside reconnection between the Earthﾕs magnetic field and solar wind magnetic field are expected to relate. We investigate the ULF waves associated with the upgoing electron beam events on the dayside (06 - 18 MLT) and discuss their relationship. We also investigate the relation between such events and solar wind parameters and discuss possible mechanisms to generate the periodic perturbations and the particle energization phenomena comparing with the similar ULF wave events on the dayside.

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

Conjunction between DMSP-CLUSTER SSM CLUSTER FGM

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

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

Up Down EFW Epole Beast FGM S ∑S

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? E B

? E B

? E B

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.