An overview of recent [SQUID]² activities.

oral presentationsession III: Couplings: solid Earth, atmosphere and near Universe

International audience

English. The passive underground system [SQUID]2 (SQUID with Shielding QUalified for Ionosphere Detection) is a three-axis helium cooled magnetometer installed within the LSBB (Laboratoire Souterrain à Bas Bruit). This permanent operating device, sheltered by a unique underground shielded cell buried under karstic rock, takes benefit of the low noise environment of the laboratory to continuously monitor the three components of the ambient magnetic field with an unrivalled sensitivity.Almost ten years of observation have revealed the potentialities of this sensitive sensor especially in detecting the Earth magnetic field variations consecutive to the ionosphere contributions (hence its name). These contributions take place at various heights of the atmosphere and depending of their origin, some of them involve coupling between the different layers of the atmosphere or between the Earth itself and its atmosphere. In this frame, it is important to appreciate the background magnetic field levels for the understanding of the Earth’s geophysical environment. The status of the current knowledge will be presented through a few results connected to low level solicitations as well as single events as solar storms and huge earthquakes, observed with the [SQUID]2 system, a peculiar attention will be given to various excitations of the mesopause resonance mode under mechanical and electromagnetic excitations.All this external perturbations are transmitted across the mountain and the transfer function for the underground observed signal depends on the water stock of the mountain. The electrical conductivity of the rock varies with water distribution inside it and determines the path of the telluric currents induced by the fluctuations of the magnetic field generated in the ionosphere. We aim to investigate the rule of the water trapped inside the rock cover height on the underground observed signal and if the attenuation of the external solicitations can be related with the evolution of the hydrogeological conditions. We present here the first results of a new device dedicated to this exploration.