ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-22-2643-2004 Cluster observations of ELF/VLF signals generated by modulated heating of the lower ionosphere with the HAARP HF transmitter Platino M. 1 Inan U. S. 1 Bell T. F. 1 Pickett J. 2 Kennedy E. J. 3 Trotignon J. G. 4 Rauch J. L. 4 Canu P. 5 Space, Telecommunications and Radioscience (STAR) Laboratory, Stanford University, Stanford, CA 94305, USA Dept. of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA Naval Research Laboratory, 4555 Overlook Ave. SW, Washington D.C. 20375, USA Laboratoire 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 Centre 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 14 07 2004 22 7 2643 2653 Copyright: © 2004 M. Platino et al. 2004 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/22/2643/2004/angeo-22-2643-2004.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/22/2643/2004/angeo-22-2643-2004.pdf

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 <i>L</i>&asymp;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.