Geomagnetic and Archeomagnetic Jerks: Where Do We Stand?



The Earth's magnetic field is generated mainly by a self-sustaining dynamo in the fluid outer core. Known as the core or main field, the dynamo's magnetic field is not constant but changes with time, a phenomenon denoted as secular variation. Unfortunately, no common agreement exists about the definition of secular variation: While some use this term for the temporal changes of the core field in general, others use the term only for its linear part (first time derivative).