Background
The Earth's magnetic field varies over a wide range of timescales. The longer-term variations, typically occurring over decades to millennia, are predominantly the result of dynamo action in the Earth's core. Geomagnetic variations on timescales of seconds to years also occur, due to dynamic processes in the ionosphere, magnetosphere and heliosphere. These changes are ultimately tied to variations associated with the solar activity (or sunspot) cycle and are manifestations of space weather.
The fact that the geomagnetic field does respond to solar conditions can be useful, for example in investigating Earth structure using magnetotellurics, but it also creates a hazard. This geomagnetic hazard is primarily a risk to technology under the Earth's protective atmospheric blanket.
Read more about this topic: Geomagnetically Induced Current
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