Small-scale structures in the high-altitude auroral electric field

Details Small-scale structures in the high-altitude auroral electric field Small-scale structures in the high-altitude auroral electric field

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995angeo..13...84a&link_type=abstract

Annales Geophysicae (ISSN 0992-7689), vol. 13, no. 1, p. 84-94

Physics

13

Auroral Arcs, Auroral Zones, Earth Magnetosphere, Electric Fields, Electrostatic Waves, High Altitude, Spatial Distribution, Spectrum Analysis, Variations, Viking Orbiter Spacecraft

Scientific paper

High-altitude (1 - 2 R(sub e)) transverse electric field fluctutations in the evening sector auroral zone as observed by the Viking satellite are studied. These events of intense (up to 300 mV/m) fluctuations (previously referred to as electrostatic shocks) occurred in the large-scale region 1 upward current and they were found to be associated with upward ion beams and enhanced upward currents. It was concluded that the intense fluctuations were observed inside and above regions of particle acceleration. Total potential drops deduced from particle measurements varied typically from 1 to 3 kV. The events occurred during quiet to moderate active conditions, with K(sub p) less than equal to 3 on seven orbits out of nine. In the power spectrum of the transverse electric field a maximum between 0.1 to 1.0 Hz was often seen, superimposed on the general decrease of power with frequency. A decrease in the frequencies of power maxima versus height was found. By transforming these frequencies to ionospheric wavelengths assuming that each frequency was produced by a Doppler shift of a constant wavelength due to satellite motion, it was found that most of the wavelengths ranged between 1 and 5 km. The most frequent value was 1 - 2 km. We propose that these structures correspond to spatial fine structure in auroral arcs, although the possibility for temporal origin (e.g. Alfven waves) of the electric field structures cannot be ruled out.

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