A. Meloni

Worldwide character of the 1991 geomagnetic jerk

A recent examination of the geomagnetic element annual mean values for the European magnetic observatories, has shown the existence of a sudden change in the secular acceleration at about 1991. In this work the space time character of the 1991 impulse is investigated and its worldwide character is evidenced; an evaluation of the amplitude spatial distribution is given for the Y component, analysing data relative to 74 magnetic observatories. The external effects were removed from the annual mean data and successively the Y secular variation has been evaluated from the corrected annual means. Moreover the worldwide character of the intensity of the step in the second time derivative is compared with the character of the previous well known jerk events of 1969 and 1978.

Geomagnetic jerks in the polar regions

[1]xa0The occurrence of geomagnetic jerks over the Arctic and Antarctic regions is here investigated. Maps of geomagnetic secular acceleration over the polar regions are produced from the CM4 and CHAOS models and the occurrence of geomagnetic jerks is associated with jumps in secular acceleration. The obtained results confirm that in Antarctica geomagnetic jerks systematically follow geomagnetic jerks in the Arctic region with a time delay from one to three years. Evidence is found of an abrupt change in secular acceleration in both polar regions around 1985, suggesting that the 1985 local jerk could actually be a worldwide event. Combining our results with the results previously obtained on the occurrence of a geomagnetic jerk at low-mid latitudes around 2003, we support the hypothesis of a global extension of an event occurred at the beginning of the 21st century.

Multifractality and punctuated equilibrium in the Earth's magnetic field polarity reversals

The Earths magnetic field has reversed its polarity hundreds of times in the Earths history. This phenomenon is generally viewed as due to a Poisson nonstationary process. Here, the geomagnetic chron time length sequence, for the past 166 Ma, is analyzed using a multifractal approach, based on ‘singularity analysis’. The existence of a multifractal structure is the signature of the occurrence of ‘punctuated equilibrium‘, which can be read as an indication of a critical configuration of the geodynamo. The results obtained are compared with those from a prototypical model of a dynamical system, introduced by Seki & Ito [1993], and are discussed in the context of fluid motions within the Earths outer liquid core.