Earth’s changing, irregular magnetic field is causing headaches for polar navigation

Earth’s liquid, molten outer core, composed mainly of iron and nickel, exerts an electromagnetic field extending from the north and south poles that protects the planet from harmful radiation from solar particles.

Fluctuations in the strength of Earth’s magnetic field – caused by daily changes in the solar wind structure and intermittent solar storms – can affect the use of geomagnetic field models that are essential for navigation in satellites, aircraft, ships and cars.

Magnetic field models differ based on the location of data collection: on or near the Earth’s surface or satellites in low Earth orbit. Past research has attributed model differences to activity levels in space, but a recent analysis of six years of Earth and satellite magnetic field models found that model differences are also caused by model errors and not just geophysical phenomena. The results are published in the Journal of Geophysical Research: Space Physics.

The University of Michigan research team assessed the differences between observations from the Swarm mission’s low Earth orbit satellites and a geomagnetic field model, the thirteenth generation of the International Geomagnetic Reference Field, or IGRF-13. They focused on differences during low to moderate geomagnetic conditions covering 98.1% of the time between the years 2014 and 2020.

Satellite observations collected at various locations above Earth are sensitive to fluctuations in the magnetic field, while Earth’s magnetic field models use observations to estimate Earth’s internal magnetic field without considering the influence of solar storms. Internal magnetic field models such as IGRF-13 are used to monitor changes in Earth’s magnetic poles, such as the shift of the North Pole of about 45 km north-northwest per year.

Understanding these major differences is important for satellite operation when using IGRF-13 as a reference and for research into the physics of Earth’s magnetosphere, ionosphere, and thermosphere.

Model uncertainty was greatest in the Arctic and Antarctic regions, and statistical analysis showed that asymmetry between the Arctic and Antarctic regions was a major factor causing model differences.

“We often assume a nearly symmetrical magnetic field between the northern and southern polar regions, but in reality they are very different,” said Yining Shi, assistant research scientist at the University of Michigan Climate and Space Science and Engineering and corresponding author of the research. .

The two geographic poles indicate different geomagnetic coordinates. The North Pole is mapped at approximately 84° Magnetic Latitude (MLAT) and 169° Magnetic Longitude (MLON) and the South Pole at approximately −74° MLAT and 19° MLON.

The polar orbit of the Swarm satellites introduces a sampling bias with a high concentration of measurements around the geographic poles, which exacerbates model discrepancies.

“Understanding that what is attributed to geophysical disturbances is actually due to the asymmetry of the Earth’s magnetic field will help us create geomagnetic field models and aid in satellite and air navigation,” said Mark Moldwin, professor at Arthur F. .Thurnau. Climate and Space Sciences and Engineering at UM and author of the study.

Another issue that worries the navigation community is that the polar magnetic field has changed rapidly over the past decade.

“This adds even more complexity to creating accurate magnetic field models,” Moldwin said.