A geomagnetic jerk for the early 1990's

Records from geomagnetic observatories in Europe are showing indications of another impulse in the third time derivative of the east component around 1991. These impulses, otherwise known as jerks, have occurred in the past at about 1925, 1969 and 1978 and possibly also 1900 and 1913. They are believed to be internal in origin and have implications for the understanding of the fluid motions in the core which create them, or for lower-mantle conductivity, or both.