Cluster observation of electron acceleration by ULF Alfv

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 electrons
  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
215330
215415
S/C-1
S/C-2
S/C-3
S/C-4
215530
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 electrons
  energy
• Electron acceleration signatures shows time
  viabilities.
• Wave forms do not look like structure.
• Several hundreds km of perpendicular wave length.
• Vortex structure.