Geomagnetic jerk features produced using synthetic core flow models

Research areas:
Year:
2019
Keywords:
Magnetic field, Geomagnetic jerks, Core flows, Secular variation, Secular acceleration
Authors:
Journal:
Physics of the Earth and Planetary Interiors
Volume:
291
Pages:
35 - 53
ISSN:
0031-9201
Abstract:
Geomagnetic jerks are the shortest temporal variations of the magnetic field generated in the Earth's core. The physical mechanism producing such abrupt changes as well as their spatio-temporal characteristics are not well understood. In order to explore geomagnetic jerks generation and their characteristics, we use a set of synthetic core flow models to solve the radial magnetic induction equation. We analyze changes of trend in the secular variation time series using a cubic polynomial fit, by invoking a new formalism of jerk amplitude per unit duration time. A new visualization scheme allows interpreting jerk amplitudes and occurrences in space and time. We find that a mild time-dependence of flow amplitude, while keeping a fixed pattern, reproduces geomagnetic jerk amplitudes. The polynomial fits were compared with two line-segments fits at ten sampled magnetic observatories about historical jerk occurrences. The differences between the misfits in the two approaches are small, which may question the definition of geomagnetic jerks as sharp “V-shape”. The local time series in our models exhibit secular acceleration changes of sign that reproduce some main observed characteristics of geomagnetic jerks: (i) a range of amplitudes that encompass those observed in geomagnetic jerks, (ii) non-simultaneous occurrence, (iii) non-global occurrence, (iv) spatial variability of amplitudes and (v) strongest amplitudes in the radial component.