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High‐resolution optical observations of a substorm expansion show dynamic auroral rays with surges of luminosity traveling up the magnetic field lines. Observed in ground‐based imagers, this phenomenon has been termed auroral flames, whereas the rocket signatures of the corresponding energy dispersions are more commonly known as field‐aligned bursts. In this paper, observations of auroral flames obtained at 50 frames/s with a scientific‐grade Complementary Metal Oxide Semiconductor (CMOS) sensor (30° × 30° field of view, 30 m resolution at 120 km) are used to provide insight into the nature of the precipitating electrons similar to high‐resolution particle detectors. Thanks to the large field of view and high spatial resolution of this system, it is possible to obtain a first‐order estimate of the temporal evolution in altitude of the volume emission rate from a single sensor. The measured volume emission rates are compared with the sum of modeled eigenprofiles obtained for a finite set of electron beams with varying energy provided by the TRANSCAR auroral flux tube model. The energy dispersion signatures within each auroral ray can be analyzed in detail during a fraction of a second. The evolution of energy and flux of the precipitation shows precipitation spanning over a large range of energies, with the characteristic energy dropping from 2.1 keV to 0.87 keV over 0.2 s. Oscillations at 2.4 Hz in the magnetic zenith correspond to the period of the auroral flames, and the acceleration is believed to be due to Alfvenic wave interaction with electrons above the ionosphere.

Publication Title

Journal of Geophysical Research: Space Physics



American Geophysical Union

Additional Information

Dahlgren, H., J. L. Semeter, R. A. Marshall, and M. Zettergren (2013), The optical manifestation of dispersive field-aligned bursts in auroral breakup arcs,J. Geophys. Res. Space Physics,118, 4572–4582, doi:10.1002/jgra.50415. To view the published open abstract, go to and enter the DOI.

Required Publisher’s Statement

An edited version of this paper was published by AGU. Copyright (2013) American Geophysical Union.