 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.