Mixing in Earth's outer core causes geomagnetic dipole to collapse

Scientists have performed numerical calculations that show how convective mixing flows in the Earth's liquid outer core can cause the geomagnetic dipole to collapse.

For the past 160 years, the Earth's magnetic dipole has been weakening at a rate of nearly six percent per century.

To gain an improved understanding of the mechanisms contributing to the dipole moment collapse, Lijun Liu, from California Institute of Technology, and Peter Olson from Johns Hopkins University, US, have performed numerical calculations to show that mixing in Earth's outer core is the culprit.

Their simulations show that as fluid mixes in the outer core, magnetic energy is transferred from the dipole to smaller scales, producing patches of reversed magnetic field at the core-mantle boundary and weakening the dipole.

They demonstrated that the rate of dipole moment decay is weakly sensitive to the particular mixing flow pattern, but varies with the magnetic Reynolds number, a measure of the velocity of the flow.

In particular, the researchers found that a mixing flow in the outer core with magnetic Reynolds number in the range of 200, which they suggest is a physically reasonable range, could account for the historically measured rate of decrease of the geomagnetic dipole moment. (ANI)

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