Ionospheric Disturbances Recorded by DEMETER Satellite over Active Volcanoes: From August 2004 to December 2010
Figure 2
(a) Example of type 1 anomaly. Electric anomaly recorded on Poas volcano on November 20, 2009, 35 days before the beginning of the eruptive activity. From top to bottom: Spectrogram of the electric field up to 500 Hz (the intensity is colour-coded according to the scale on the right), spectrogram of the magnetic field up to 500 Hz, and ion densities (H+ in blue, O+ in red, and He+ in green). The closest approach to the volcano is between 03:18:30 (90 km) and 03:19:30 UT (120 km). The blue rectangular indicates how the distance of the footprint of the satellite moves. (b) Example of type 2 anomaly. Electric (top panel) and magnetic (bottom panel) anomalies recorded on Asama volcano on December 30, 2008, 22 days before the eruption. The electric spectrogram is up to 15 kHz, whereas the magnetic one is up to 1 kHz. The closest approach to the volcano is at 01:07:30 UT (15 km). The blue rectangle that indicates how the distance of the footprint of the satellite moves. (c) Example of type 3 anomaly. Time elongated electric anomaly recorded on Soputan volcano on May 26, 2008, 10 days before the onset of surface activity. Electric (top panel) and magnetic (bottom panel) spectrograms are up to 300 Hz. The closest approach to the volcano is at 13:44:30 UT (35 km). The blue rectangular indicates how the distance of the footprint of the satellite moves. (d) Example of type 4 anomaly. Change in electronic (top panel) and ionic (bottom panel (O+ in red, and He+ in green)) densities recorded on Kirishima volcano on February 22, 2010, 36 days before the surface activity started. The closest approach to the volcano is at 13:02:00 UT (470 km). The blue rectangular indicates how the distance of the footprint of the satellite moves. (e) Example of type 5 anomaly. Decrease of the energy content in the electric and magnetic fields recorded on La Fournaise volcano on August 31, 2008, 21 days before beginning of opening of active fissures. From top to bottom: spectrogram of the electric field up to 800 Hz (the intensity is colour-coded according to the scale on the right), spectrogram of the magnetic field up to 800 Hz, and the O+ density. The closest approach to the volcano is at 06:08:30 UT (105 km). The blue rectangular indicates how the distance of the footprint of the satellite moves.
