Abstract
Abstract The rate of secular variation occasionally undergoes a sudden, sharp change, called a geomagnetic jerk. Such jerks have been detected in geomagnetic time series, centered—over the last four decades—around 1971, 1980, 1991, and 1999; others have been inferred from historical records. The geomagnetic jerks represent a reorganization of the secular variation, implying an internal origin, as established through spherical harmonic and wavelet analysis. However, some characteristics of jerks are not well understood. Here we estimate the occurrence dates for geomagnetic jerks, as they can be detected from a global geomagnetic model. This choice makes the present study novel, for two reasons. First, utilizing the comprehensive modelling approach allows for the use of a secular variation signal free of time-varying external fields and their corresponding induced counterpart, and observatory biases. Second, the model utilizes satellite data when available, in addition to observatory data. Indeed, POGO (1967 to 1971), MAGSAT (1979 to 1980), Ørsted (1999 to present time) and CHAMP (2000 to present time) satellite measurements help to separate the different magnetic sources. In this study the CM4 comprehensive model is used for a global search of geomagnetic jerks and their occurrence dates. Our first result indicates that found geomagnetic jerks might not have been worldwide in occurrence. Moreover, the obtained dates suggest that jerks detected in the CM4 model over the last four decades occurred not simultaneously but at slightly different times around 1971, 1980 and 1991.
Highlights
The magnetic field, observed on the surface of the Earth, is mainly generated in the external core
The secular variation usually occurs as smooth time changes of the core field, episodes of abrupt changes have occurred in the past
To find the mean epoch for each event we considered the results obtained in detection and characterisation of geomagnetic jerks in observatory monthly series using the wavelet analysis method
Summary
The magnetic field, observed on the surface of the Earth, is mainly generated in the external core. The external magnetic field is generated from magnetic sources outside the Earth, and is mainly produced by tidal motions in the ionosphere and interactions of the Earth’s magnetosphere with the solar wind. Another source is the externally induced field by currents flowing within the Earth’s crust and mantle. The secular variation usually occurs as smooth time changes of the core field, episodes of abrupt changes have occurred in the past. These are known as geomagnetic jerks or geomagnetic impulses (Courtillot et al, 1978).
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