Magnetotellurics
The magnetotelluric (MT) method is a passive geophysical technique that measures Earth's naturally occurring electric and magnetic fields. The MT method is utilized to measure frequencies smaller than 1 Hz which are mainly sourced from Earth's geoelectric field.
Activity on the sun dictates particle flux, speed, and direction in space which causes perturbations in Earth's magnetosphere which induces a current in the ionosphere via Faraday's law. Currents induced in the ionosphere produce low frequency electric and magnetic fields on the surface of the Earth that are measured using the magnetotelluric method.
The electric field is measured using four calibrated electrodes engineered into dipoles. Each dipole set oriented in the north to south, and the east to west direction is separated by 100 meters of insulated copper wire. The currents induced in the geoelectric field are detected by the dipoles set up on the surface of the Earth. A fluxgate magnetometer orthogonally oriented to the set of dipoles measures the magnetic field induced from the ionospheric currents.
The electric and magnetic field data is collected for approximately one month at each site. When field checks and services yield quality data, the instrument is removed and data is sent to processing where the raw data time series are windowed and convoluted to the frequency domain. Data is then inverted for the transfer functions where results are graphed on a log plot apparent resistivity vs. period. The data estimates the ground conductivity structure at depths ranging from hundreds of meters to hundreds of kilometers below the surface. The transfer functions for stations collected to date can be found here.
Collection of the electric and magnetic field components on the Earth's surface are pertinent to understanding and predicting hazards related to GIC. MT
In addition to GIC hazard mapping, the MT method is used to model the Earth's crust and upper mantle. Imaging depth slices of earth allows researchers to better understand plate tectonics and dynamic processes.
Geomagnetically Induced Currents
Geomagnetically induced currents (GIC) are currents induced in technological systems on Earth. GIC originate from the influence of space weather interacting with Earth's magnetic field. Significant space weather events can manifest from coronal mass ejections (CME), bursts of plasma released on the surface of the sun, and waves of radiation from solar flares. These events are characterized by dark spots (umbra and penumbra); representing the changing magnetic fields on the sun.
Space weather consists of solar winds that shape and structure Earth’s magnetosphere and drives key processes such as magnetic reconnection, convection, current systems, and particle precipitation (which produce the aurora).
Increased magnitude of space weather events can cause auroras to extend to mid latitudes proximal to the equator.
Ionospheric ground interactions from space weather occur at frequencies below 1Hz and periods less than 1 second. Travelling ionospheric disturbances (TID) are related to atmospheric compression from solar wind and can be measured using the magnetotelluric method.
Space weather influence on Earth increases corrosion of steel pipelines, and damage to high voltage power transformers. Space weather can produce electromagnetic fields that induce extreme GIC in wires, disrupting power lines and wide-spread blackouts. The Carrington event of 1859 impacted….The Hydro- Quebec blackout in 1989 was onset by a magnetic storm which resulted in power loss for several hours. Further out in space, in July 2000, a CME (x-5 classification) caused a large enough particle burst to damage the camera and electrical sensors on the SOHO satellite. Historic events related to GIC have caught the attention of scientists spanning disciplines from astrophysics, atmospheric sciences, and geophysics.
Mitigation of hazards related to GIC include and are not limited to: USGS, NGF, UCAR, NOAA, FEMA, NASA, IRIS, and many more.