The active experiments

Numerous active experiments have been performed in association with Demeter. They are mainly related to ionospheric heating at high latitudes with powerful transmitters as HIPAS and HAARP in Alaska (Platino et al., 2006), Sura in Russia, and EISCAT in Norway (Tromsoe). A carrier wave at a frequency of several MHz is emitted with a modulation to change the ionospheric conductivity by heating. The current of the polar electrojet is then modulated and produces waves in the ELF/VLF range (Figures 34 et 35). These experiments allow to study the wave propagation and their effects on the radiation belts. Another experiment was also done in Ukrainia to study the propagation of an acoustic wave up to the satellite altitude.

Figure 34: Spectrogram registered on July 29, 2007 when Demeter is above HAARP. Pulses and ramps have been generated in the ionosphere.

Figure 35: Spectrogram registered on August 23, 2007 in a conjugated region of Alaska in the South hemisphere. The pulses generated by HAARP have been propagated along the magnetic field lines. One can also see at the end of some pulses supplementary triggered emissions which are due to interaction with energetic particles.