Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 35, 493-503, 2017
https://doi.org/10.5194/angeo-35-493-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
28 Mar 2017
Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution
Hanna Dahlgren1,2, Betty S. Lanchester2, Nickolay Ivchenko1, and Daniel K. Whiter2 1School of Electrical Engineering, Royal Institute of Technology KTH, Stockholm, Sweden
2School of Physics and Astronomy, University of Southampton, Southampton, UK
Abstract. High-resolution multispectral optical and incoherent scatter radar data are used to study the variability of pulsating aurora. Two events have been analysed, and the data combined with electron transport and ion chemistry modelling provide estimates of the energy and energy flux during both the ON and OFF periods of the pulsations. Both the energy and energy flux are found to be reduced during each OFF period compared with the ON period, and the estimates indicate that it is the number flux of foremost higher-energy electrons that is reduced. The energies are found never to drop below a few kilo-electronvolts during the OFF periods for these events. The high-resolution optical data show the occurrence of dips in brightness below the diffuse background level immediately after the ON period has ended. Each dip lasts for about a second, with a reduction in brightness of up to 70 % before the intensity increases to a steady background level again. A different kind of variation is also detected in the OFF period emissions during the second event, where a slower decrease in the background diffuse emission is seen with its brightness minimum just before the ON period, for a series of pulsations. Since the dips in the emission level during OFF are dependent on the switching between ON and OFF, this could indicate a common mechanism for the precipitation during the ON and OFF phases. A statistical analysis of brightness rise, fall, and ON times for the pulsations is also performed. It is found that the pulsations are often asymmetric, with either a slower increase of brightness or a slower fall.

Citation: Dahlgren, H., Lanchester, B. S., Ivchenko, N., and Whiter, D. K.: Variations in energy, flux, and brightness of pulsating aurora measured at high time resolution, Ann. Geophys., 35, 493-503, https://doi.org/10.5194/angeo-35-493-2017, 2017.
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Short summary
Pulsating aurora are ubiquitous events that constitute a large amount of energy transfer to the ionosphere. Still there are unsolved issues regarding their formation. Using high-resolution optical and radar data, we find that it is the flux of high-energy electrons that get reduced during the OFF period of the pulsations. We also report on dips in brightness at the transition between ON and OFF, and asymmetric rise and fall times, which may have implications for understanding the pulsations.
Pulsating aurora are ubiquitous events that constitute a large amount of energy transfer to the...
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