Why does the earth’s magnetic field have ‘weak spots’?

Researchers analysed data from the European Space Agency’s ‘Swarm’ mission and recently reported that the South Atlantic Anomaly, the region of weakest intensity in the earth’s magnetic field, has expanded since 2014. Today, according to the data, it covers about 0.9% more of the earth’s surface than it did in 2014.

The field has weak spots because the molten iron and nickel circulating in the earth’s outer core don’t move uniformly. Their motion generates the field in a process called the geodynamo. Since the flow is uneven, there are regions where the magnetic flux is concentrated and others where it spreads out.

The earth’s field is continuously reorganised as the fluid core moves, and the weak regions can expand, shrink or migrate over decades without threatening the planet’s overall magnetic shield or indicating a magnetic reversal.

Indeed, the study’s authors have stressed that despite the Anomaly’s apparent expansion, there is no reason for alarm since such changes are part of the natural variation of the geomagnetic field. They’ve also said that the observed rates of changes are within expected limits and don’t signal an impending field reversal or collapse.