Measurements and uncertainties of the occurrence time of the 1969, 1978, 1991, and 1999 geomagnetic jerks

Abstract

[1] Geomagnetic jerks are rapid time variations of the magnetic field at the Earth's surface that are thought to be of primarily internal origin. Jerks are relevant for studies of the Earth interior: they likely give information on core dynamics and possibly on mantle electrical conductivity. In such studies a precise determination of the jerk occurrence time and its error bar at each observatory is required. We analyze the most well-known global jerks (1969, 1978, and 1991) and a possible local jerk in 1999, considering all three components of the magnetic field (X, Y, and Z). Different data sets are investigated: annual means, 12 month running averages of observatory monthly means in rotated geomagnetic dipole coordinates, and data representing the core field contribution synthesized from the CM4 time-dependent field model. The secular variation in each component of the field around the time of a jerk was modeled by two straight line segments, using both least squares and 1-norm methods. The 1969The , 1978, and 1991 jerks were globally detected, while the 1999 event was only locally identified. Using this simple method enables us to calculate error bars in the jerk occurrence times and to quantify their nonsimultaneous behavior. We find that our error bars are not, in general, symmetric about the mean occurrence time and that the mean errors on the X and Z components of 1.7 years and 1.5 years are larger than that of 1.1 years on the Y component. Generally, the error bars were found to be larger in the Southern Hemisphere observatories. Our results are necessary prerequisites for further studies of the inverse problem that attempt to determine mantle electrical conductivity from variations in jerk occurrence times.

Evidence for a new geomagnetic jerk in 2014

“…The determination of the jerk amplitudes at each observatory was made using the method proposed by Pinheiro et al [2011], i.e., evaluating the SV slopes before and after the jerk and subtracting the former from the latter. The determination of the jerk amplitudes at each observatory was made using the method proposed by Pinheiro et al [2011], i.e., evaluating the SV slopes before and after the jerk and subtracting the former from the latter.…”

“…Working in parallel, the French and British groups observed the same phenomenon (now accepted as the 1969 jerk), although the book in which the British group published their paper appeared later because of some editorial difficulties (D. R. Barraclough and J. O. Cardús, personal communications). For an extensive review of geomagnetic jerks, their nature, and the different ways to isolate them, we refer to Mandea et al [2010], Pinheiro et al [2011], or Brown et al [2013. Since then, several other jerks have been detected.…”

The 2014 geomagnetic jerk as observed by southern African magnetic observatories

“…Mandea et al 2010;Pinheiro et al 2011;Brown et al 2013). Secular acceleration (SA) pulses in the Earth's geomagnetic field during the last decade have been identified by Chulliat et al (2010) using primarily data from the CHAMP satellite and magnetic observatories.…”

Geomagnetic field declination: from decadal to centennial scales

“…The 10 geomagnetic jerks have been treated as chaotic fluctuations of the field by Qamili et al (2013). Brown et al (2013) have been interested in the sharp time changes in the secular variation, using an improved method to account for the external variations in data (Wardinski and Holme, 2011) and for a jerk identification (Pinheiro et al, 2011); they find by far more events than had previously been determined, with a general trend of increased number of identified jerks towards the end of the 20 th century and beginning of the 21 st century. The new satellite era offers high resolution magnetic data and the 15 possibility to deeply investigate these events.…”