On Wednesday, March 7, a large solar flare ejected a massive stream of charged particles from the solar atmosphere. This “coronal mass ejection”, or CME, was unusually strong, causing an increase in the background stream of particles emitted from the sun, known as the solar wind. By the following day, the trajectory of the CME brought it past the ACE (Advanced Composition Explorer) spacecraft, which detected the shock from the CME at 10:45 (Universal Time, or UT). The CME then came into contact with the Earth’s magnetic field, where it set up a series of intense electric currents above the outer reaches of the atmosphere. These electric currents, whose intensity changes rapidly with time, induced electric currents to flow in the Earth and ocean. Researchers making use of EarthScope’s USArray Magnetotelluric Observatory take advantage of these high altitude electric currents as a signal source.
For the first time investigators will be able to determine the 3D variations in the electrical conductivity of the crust and mantle on a truly continental scale. The conductivity of geologic formations is strongly related to the presence of fluids, including magma and brines, the composition and type of rock, its temperature, and the presence of minerals. The EarthScope Magnetotelluric Observatory, through a subcontract from IRIS to Oregon State University, and with the collaboration of investigators across the US, maintains seven permanent stations (installed in Oregon, California, Montana, New Mexico, Missouri, Minnesota and Virginia) and operates a movable array of temporary stations that are systematically mapping out the electrical conductivity structure of the crust and mantle across the continental US on a 70-km spaced grid of observation stations.
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