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Ann. Geophys., 22, 2643-2653, 2004
www.ann-geophys.net/22/2643/2004/
© European Geosciences Union 2004
Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter
M. Platino1, U. S. Inan1, T. F. Bell1, J. Pickett2, E. J. Kennedy3, J. G. Trotignon4, J. L. Rauch4, and P. Canu5
1Space, Telecommunications and Radioscience (STAR) Laboratory, Stanford University, Stanford, CA 94305, USA
2Dept. of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
3Naval Research Laboratory, 4555 Overlook Ave. SW, Washington D.C. 20375, USA
4Laboratoire de Physique et Chimie de l’Environnement, Centre National de la Recherche Scientifique, 3 A avenue de la Recherche Scientifique, F-45071 Orléans cedex 02, France
5Centre d’Etudes des Environnements Terrestres et Planétaires, Centre National de la Recherche Scientifique, Université Versailles Saint-Quentin-en-Yvelines, 10 avenue de l’Europe, F-78140, Vélizy Villacoublay, France
Abstract. It is now well known that amplitude modulated HF
transmissions into the ionosphere can be used to generate ELF/VLF signals
using the so-called "electrojet antenna". Although most observations of the
generated ELF/VLF signals have been made on the ground, several low and
high-altitude satellite observations have also been reported (James et al., 1990). One of
the important unknowns in the physics of ELF/VLF wave generation by
ionospheric heating is the volume of the magnetosphere illuminated by the
ELF/VLF waves. In an attempt to investigate this question further,
ground-satellite conjunction experiments have recently been conducted using
the four Cluster satellites and the HF heater of the High-Frequency Active
Auroral Research Program (HAARP) facility in Gakona, Alaska. Being located
on largely closed field lines at L≈4.9, HAARP is currently also
being used for ground-to-ground type of ELF/VLF wave-injection experiments,
and will be increasingly used for this purpose as it is now being upgraded
for higher power operation. In this paper, we describe the HAARP
installation and present recent results of the HAARP-Cluster experiments.
We give an overview of the detected ELF/VLF signals at Cluster, and a
possible explanation of the spectral signature detected, as well as the
determination of the location of the point of injection of the HAARP ELF/VLF
signals into the magnetosphere using ray tracing.
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