EarthRef.org Reference Database (ERR) -- De Michelis et al. 1998

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. ¿ 1998 American Geophysical Union 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. ¿ 1998 American Geophysical Union