An EISCAT study of a pulsating auroral arc: simultaneous ionospheric electron density, auroral luminosity and magnetic field pulsations

Abstract

We present a case study of a pulsating auroral are using EISCAT incoherent scatter radar measurements of energetic electron precipitation ∼ 5–30 keV) combined with ground-based observations of auroral luminosity and magnetic pulsations. The event under consideration occurred during a magnetically quiet period on 1 February 1987 between 0:00 and 0:30 UT. Pronounced pulsations with a period of about 1 min were present in all measured quantities. The magnetic pulsations of this period exhibited in phase oscillations over the spatial scale of the EISCAT Magnetometer Cross (some 250 km in longitude and 1000 km in latitude). Spectral analysis revealed also variations of a shorter time scale of about 10 s in all measured quantities except for the flux of precipitating electrons having energies below 10 keV (above 10 keV the electron flux exhibited 10 s variations). In the framework of the cyclotron resonant interaction of electrons with whistler waves, the long period pulsations are attributed to temporal modulation of the energetic electron source. The simultaneously observed pulsations with a period of about 10 s are explained within the self-oscillating regime of the whistler cyclotron instability in the magnetosphere. We present computational results from a self-consistent instability model taking all the conjectured effects into account.