Induced Geoelectric Fields as a Key Space Weather Variable

Many of the effects of geomagnetic field variations, apart from those on devices using the geomagnetic field directly, are through induction of electric fields as described by Faraday’s Law. Such electric fields in turn cause an Ohmic effect in the Earth and conducting infrastructure, giving rise to potentially harmful geomagnetically induced currents (GIC). Precise measurement of the geomagnetic field dates back nearly two centuries, but localized measurements of geoelectric fields started mostly with magnetotelluric prospecting only in the mid-twentieth century. For this historical reason, and due to measuring difficulties now circumvented by modern technology, direct detection of geoelectric fields for space weather applications has rarely been done. We will describe efforts at Athabasca University to measure geomagnetic and geoelectric fields with a wide range of equipment, from commercial coil-based systems at 2400 Hz to extremely inexpensive systems based on microcontrollers and analog front ends. In principle, geoelectric field measurement devices can be simplified, and made inexpensive, more readily than those for geomagnetic fields, making networks of them a good way to monitor localized GIC effects. Recent cases of detection of large geoelectric fields in our region will be discussed.