geophysics Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' so ...

, a geomagnetic jerk or secular geomagnetic variation impulse is a relatively sudden change in the

second derivative In calculus, the second derivative, or the second order derivative, of a function is the derivative of the derivative of . Roughly speaking, the second derivative measures how the rate of change of a quantity is itself changing; for example, ...

of the

Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic ...

with respect to time. These events were noted by

Vincent Courtillot Vincent E. Courtillot (born 6 March 1948) is an emeritus French geophysicist, prominent among the researchers who are critical of the hypothesis that impact events are a primary cause of mass extinction of life forms on the Earth. He is known for ...

and Jean-Louis Le Mouël in 1976. The clearest ones, observed all over the world, happened in 1969, 1978, 1991, and 1999. Data before 1969 is scarcer, but there is evidence of other global jerks in 1901, 1913, and 1925. Other events in 1932, 1949, 1958, 1986, and 2003 were detected only in some parts of the world. These events are believed to originate in the interior of the Earth (rather than being due to external phenomena such as the

solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sol ...

); but their precise cause is still a matter of research. The name "jerk" was borrowed from kinematics, where it means the rate of change of the acceleration of a body, that is, the third derivative of its position with respect to time (the

acceleration In mechanics, acceleration is the rate of change of the velocity of an object with respect to time. Accelerations are vector quantities (in that they have magnitude and direction). The orientation of an object's acceleration is given by t ...

being the second derivative); or, more specifically, a sudden and momentary spike (or dip) in that rate.

Description

Jerks seem to occur in irregular intervals, on average about once every 10 years. In the period between jerks, each component of the field at a specific location changes with time ''t'' approximately as a fixed

polynomial In mathematics, a polynomial is an expression consisting of indeterminates (also called variables) and coefficients, that involves only the operations of addition, subtraction, multiplication, and positive-integer powers of variables. An example ...

of the second degree, ''A'' ''t''² + ''B'' ''t'' + ''C''. Each jerk is a relatively sudden change (spread over a period of a few months to a couple of years) in the ''A'' coefficient of this formula, which determines the second derivative; and usually in ''B'' and ''C'' coefficients as well. The strength of each jerk varies from location to location, and some jerks are observed only in some regions. For example, the 1949 jerk was clearly observed at

Tucson , "(at the) base of the black ill , nicknames = "The Old Pueblo", "Optics Valley", "America's biggest small town" , image_map = , mapsize = 260px , map_caption = Interactive map ...

( North America, long. 110.93°), but not at Chambon la Forêt (

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

, long. 2.27°). Moreover, the global jerks seem to occur at slightly different times in different regions; often earlier in the Northern hemisphere than in the Southern hemisphere.

Theories

These events are believed to be caused by changes in the flow patterns of the liquid outer core of the Earth, as for instance carried by hydromagnetic waves such as torsional oscillations. Numerical simulations of core dynamics have successfully reproduced the characteristics of well documented jerks. In these simulations, jerks are caused by

Alfvén wave In plasma physics, an Alfvén wave, named after Hannes Alfvén, is a type of plasma wave in which ions oscillate in response to a restoring force provided by an effective tension on the magnetic field lines. Definition An Alfvén wave is ...

s emitted inside the

outer core Earth's outer core is a fluid layer about thick, composed of mostly iron and nickel that lies above Earth's solid inner core and below its mantle. The outer core begins approximately beneath Earth's surface at the core-mantle boundary and e ...

and focusing at the core surface. Prior to these explanations there had also been claims that geomagnetic jerks were connected to strong earthquakes.

References

{{DEFAULTSORT:Geomagnetic Jerk Geomagnetism