Abstract
Extreme variations in the direction of Earth’s magnetic field contain important information regarding the operation of the geodynamo. Paleomagnetic studies have reported rapid directional changes reaching 1° yr−1, although the observations are controversial and their relation to physical processes in Earth’s core unknown. Here we show excellent agreement between amplitudes and latitude ranges of extreme directional changes in a suite of geodynamo simulations and a recent observational field model spanning the past 100 kyrs. Remarkably, maximum rates of directional change reach ~10° yr−1, typically during times of decreasing field strength, almost 100 times faster than current changes. Detailed analysis of the simulations and a simple analogue model indicate that extreme directional changes are associated with movement of reversed flux across the core surface. Our results demonstrate that such rapid variations are compatible with the physics of the dynamo process and suggest that future searches for rapid directional changes should focus on low latitudes.
Highlights
Extreme variations in the direction of Earth’s magnetic field contain important information regarding the operation of the geodynamo
We search for extreme changes in field direction in GGF100k and in a suite of 16 dynamo simulations that produce a range of dynamical behaviour and reproduce various features of the geomagnetic field
Our suite of geodynamo simulations span a wide range of physical parameters and access reversing and non-reversing dynamo regimes; as with all current models, they still do not reach the low values of the Ekman number E and magnetic Prandtl number Pm that characterise Earth’s core
Summary
Extreme variations in the direction of Earth’s magnetic field contain important information regarding the operation of the geodynamo. Paleomagnetic studies have reported rapid directional changes reaching 1° yr−1, the observations are controversial and their relation to physical processes in Earth’s core unknown. 1234567890():,; The large-scale secular variation of Earth’s internally generated magnetic field is reasonably well-established by global models based on observations spanning the past two decades[1] and the historical period[2] Prominent features of these models, such as the difference in activity between Atlantic and Pacific hemispheres and rapid changes at high latitudes, have been linked, respectively, to thermal interactions between the core and mantle[3,4] and accelerating jets in the core[5], and to the operation of the geodynamo. This allows us to compare the whole spectrum of directional changes between simulations and observational field models
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