Simultaneous observations of ELF waves from an artificially modulated auroral electrojet in space and on the ground
Article first published online: 20 SEP 2012
Copyright 1984 by the American Geophysical Union.
Journal of Geophysical Research: Space Physics (1978–2012)
Volume 89, Issue A3, pages 1655–1666, 1 March 1984
How to Cite
1984), Simultaneous observations of ELF waves from an artificially modulated auroral electrojet in space and on the ground, J. Geophys. Res., 89(A3), 1655–1666, doi:10.1029/JA089iA03p01655., , , , and (
- Issue published online: 20 SEP 2012
- Article first published online: 20 SEP 2012
- Manuscript Accepted: 2 NOV 1983
- Manuscript Received: 11 AUG 1983
Radio waves at frequencies between 525 and 5850 Hz were observed simultaneously on the ground and in the VLF receiver of the ISIS 1 spacecraft during a flight over the Max-Planck-Institut für Aeronomie ionospheric heater near Tromsø, Norway, on December 9, 1981. The heater carrier frequency, 4.04 MHz, was amplitude modulated with a set of four frequencies: 525, 1725, 2925, and 4125 Hz. The satellite detected all these fundamental frequencies plus harmonics of the 525 Hz and 2925 Hz components, caused by the nonsinusoidal modulation of the carrier. Characteristics of the signal received along the satellite track are in approximate agreement with the results of three-dimensional ray tracing applied to a model of the ionosphere around Tromsø. The time dispersion of the signals is best fitted with an ionospheric density model based on real time data with relatively low peak values. Observed signal levels have been transformed to power flux by using a plasma dipole theory and wave polarization information obtained from the three-dimensional ray solutions. Through the use of a magnetoplasma dipole theory for the induced D/E region current, the observed levels are found to correspond to radiation created by effective dipole currents between about 1.0 and 100 A. The geometrical optics theory also predicts two solutions for rays reaching a given satellite point near the polar limit of the reception zone, and a northern limit corresponding to a caustic surface. The frequencies of signal fades observed in this region are also predicted by the geometrical optics theory, but the fade depths are not. Simultaneous ground observations correspond to source region currents of about 1 A or less. Also, the ELF waves observed on the ground have different harmonic signal ratios and much smaller fluctuations than those observed on ISIS.