Communication Dans Un Congrès Année : 2009

A New Tool for Earth-Ionosphere Interactions: [SQUID]2 Ultra Low Noise 3 Axis SQUID Magnetometer, status and perspectives

Résumé

Each ground movement on Earth shakes the air column above it. When the acoustic wave reaches the ionosphere floor, charges are temporarily displaced, parallel to the acoustic excitation. An electric current is created giving birth to a magnetic signal. The density difference between ground and air makes the coupling very poor but this is compensated by very large amplification of displacement with respect to the ground one. To detect these signals we used [SQUID]2 . [SQUID]2 is a low Tc Superconducting QUantum Interferometer Device in a 3 axis magnetometer configuration inside a Shielding QUalified for Ionosphere Detection (noise level : 2fT/&surd; Hz above 40Hz without µ metal). This set-up is buried below 518m of karst in the Low Noise Underground Laboratory of Rustrel-Pays d'Apt (France),it allows the detection of these magnetic signals. For ionosphere responses to P waves, either above the epicenter or above our lab, the response for quakes M>3 is non linear: a resonance mode of the ionosphere floor is excited whose period is around 60 to 80 seconds. The same type of signal has been observed one hour before the Sichuan quake of May 2008, in time coincidence with observation of rainbow colored clouds in the surrounding area. S and T Earth breathing modes of the Earth interaction with the ionosphere were observed above the /f noise background during a magnetically quiet 72 hours time window with no quake M>5.2 . Since the frequencies of these modes are in the millihertz range, wherever such an instrument is on Earth, it is always electromagnetically near the signal source . In addition the ionosphere response is linear: each detected mode is obtained with a 1% precision with respect to the PREM model. If one consider that instruments of this type allows also the observation at mid latitude of magnetic storms with a sensitivity at least equivalent to conventional polar magnetometer, it is worthwhile to discuss the feasibility of a world wide network of SQUID stations, even with more modest noise performance.
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hal-04751580 , version 1 (24-10-2024)

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  • HAL Id : hal-04751580 , version 1

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G. Waysand, Elisabeth Pozzo-Di-Borgo, J. Marfaing, Bois J.J., R. Blancon, et al.. A New Tool for Earth-Ionosphere Interactions: [SQUID]2 Ultra Low Noise 3 Axis SQUID Magnetometer, status and perspectives. AGU Fall meeting, Dec 2009, San Francisco, United States. ⟨hal-04751580⟩
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