Abstract

Electron spectrometer measurements from polar‐orbiting satellites frequently show narrow regions of enhanced fluxes of electrons in the energy range from a few electron volts to less than 1 keV. These suprathermal electron bursts are observed throughout the auroral zone even under quiet conditions. They are typically distributed in latitude for hundreds of kilometers on either side of an upward current region which sometimes also contains an inverted V event. Whereas in inverted Vs the electron spectrum shows a peak at an energy of a few keV, suprathermal electron bursts are characterized by enhanced fluxes at all energies below a cutoff energy that is usually less than 1 keV. We present observational evidence to show that suprathermal electron bursts are correlated with enhancements in the ac electric field at frequencies below 1 kHz. The wave spectrum above 1 kHz does not differ significantly within and outside a burst. These observations suggest that the electrons in suprathermal bursts are heated through interaction with waves, most likely ion cyclotron waves. The phenomenology of suprathermal bursts indicates that the waves are not generated on the same field line at which the heating is observed. The evidence suggests that the waves are generated in regions of upward field‐aligned currents and propagate obliquely away from the source region. Electrons with parallel velocities equal to the parallel phase velocity of the waves can be heated through Landau resonance. This accounts for the fact that the cutoff energy in the bursts is never higher than the peak energy of the associated inverted V precipitation, even though the inverted V precipitation may be latitudinally displaced by several hundred kilometers from the burst.

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