Geomagnetic jerk
Encyclopedia
In geophysics
, a geomagnetic jerk or secular geomagnetic variation impulse is a relatively sudden change in the second derivative of the Earth's magnetic field with respect to time.
These events were noted by Courtillot and others in 1978. 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
); but their precise cause is still a matter of research.
The name "jerk" was borrowed from dynamics
, 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
being the second derivative); or, more specifically, a sudden and momentary spike (or dip) in that rate.
of the second degree, A t2 + 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 (North America
, long.
249.17°), but not at Chambon la Forêt (Europe
, 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.
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
, a geomagnetic jerk or secular geomagnetic variation impulse is a relatively sudden change in the second derivative of the Earth's magnetic field with respect to time.
These events were noted by Courtillot and others in 1978. 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
Solar wind
The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...
); but their precise cause is still a matter of research.
The name "jerk" was borrowed from dynamics
Analytical dynamics
In classical mechanics, analytical dynamics, or more briefly dynamics, is concerned about the relationship between motion of bodies and its causes, namely the forces acting on the bodies and the properties of the bodies...
, 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
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
being the second derivative); or, more specifically, a sudden and momentary spike (or dip) in that rate.
Description
Jerks seem occur in irregular intervals, in the 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 polynomialPolynomial
In mathematics, a polynomial is an expression of finite length constructed from variables and constants, using only the operations of addition, subtraction, multiplication, and non-negative integer exponents...
of the second degree, A t2 + 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
Coefficient
In mathematics, a coefficient is a multiplicative factor in some term of an expression ; it is usually a number, but in any case does not involve any variables of the expression...
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 (North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, long.
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
249.17°), but not at Chambon la Forêt (Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, 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.