geophysics Geophysics () is a subject of natural science concerned with the physical processes and Physical property, properties of Earth and its surrounding space environment, and the use of quantitative methods for their analysis. Geophysicists conduct i ...

, 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 . Informally, the second derivative can be phrased as "the rate of change of the rate of change"; for example, the secon ...

of the

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

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 Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

); but their precise cause is still a matter of research. The name "jerk" was borrowed from

kinematics In physics, kinematics studies the geometrical aspects of motion of physical objects independent of forces that set them in motion. Constrained motion such as linked machine parts are also described as kinematics. Kinematics is concerned with s ...

, 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 (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...

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 a Expression (mathematics), mathematical expression consisting of indeterminate (variable), indeterminates (also called variable (mathematics), variables) and coefficients, that involves only the operations of addit ...

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 In mathematics, a coefficient is a Factor (arithmetic), multiplicative factor involved in some Summand, term of a polynomial, a series (mathematics), series, or any other type of expression (mathematics), expression. It may be a Dimensionless qu ...

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 Tucson (; ; ) is a city in Pima County, Arizona, United States, and its county seat. It is the second-most populous city in Arizona, behind Phoenix, Arizona, Phoenix, with a population of 542,630 in the 2020 United States census. The Tucson ...

(

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

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

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

, 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 Magnetic tension force, effective tension on the magnetic field lines. Definition ...

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 Earth's inner core, inner core and below its Earth's mantle, mantle. The outer core begins approximately beneath Earth's surface ...

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

Description

Theories

See also

References