Earth’s shifting magnetic field causes headaches for polar navigation

Changes in the Earth's global magnetic field over six months in 2014 as measured by the European Space Agency's three-satellite Swarm constellation. The left map shows the average magnetic field and the right shows changes in magnetic field strength during that period. Credit: European Space Agency/Technical University of Denmark (ESA/DTU Space).

The Earth’s magnetic field, generated by the movement of liquid iron and nickel in its outer core, protects us from harmful solar radiation.

This magnetic field stretches from the North Pole to the South Pole. However, it is not constant; it fluctuates due to daily changes in solar wind and occasional solar storms.

These fluctuations can cause problems for navigation systems in satellites, planes, ships, and cars, which rely on geomagnetic field models.

Geomagnetic field models vary based on where the data is collected—either near the Earth’s surface or from satellites in low Earth orbit. Previously, differences in these models were thought to be mainly due to space weather activity.

However, a recent study by the University of Michigan, published in the Journal of Geophysical Research: Space Physics, found that these discrepancies are also caused by errors in the models themselves, not just by geophysical phenomena.

The research team compared data from the Swarm mission’s low-Earth orbit satellites with the International Geomagnetic Reference Field (IGRF-13) model, which estimates the Earth’s internal magnetic field.

They focused on low to moderate geomagnetic conditions, which occur 98.1% of the time between 2014 and 2020. They discovered significant differences between satellite observations and the IGRF-13 model.

Satellite data is highly sensitive to magnetic field fluctuations, while the IGRF-13 model primarily uses surface observations and does not fully account for solar storm effects. This model helps track changes in the Earth’s magnetic poles, such as the North Pole’s movement of about 45 km northwest each year.

Understanding these differences is crucial for satellite operations and research on the Earth’s magnetosphere, ionosphere, and thermosphere. The study found that model discrepancies were most significant in the polar regions, and a major factor was the asymmetry between the North and South Poles.

“We often assume that the magnetic field is nearly symmetrical between the northern and southern polar regions, but they are actually very different,” said Yining Shi, an assistant research scientist at the University of Michigan and the study’s lead author.

The North Pole maps to around 84° Magnetic Latitude (MLAT) and 169° Magnetic Longitude (MLON), while the South Pole maps to around −74° MLAT and 19° MLON. The Swarm satellites’ polar orbit track results in a high concentration of measurements around the poles, which increases the model differences.

“Recognizing that what we thought were geophysical disturbances are actually due to the asymmetry of the Earth’s magnetic field will help us improve geomagnetic field models and aid in satellite and aviation navigation,” said Mark Moldwin, a professor at the University of Michigan and co-author of the study.

Additionally, the rapid changes in the polar magnetic field over the past decade add more complexity to creating accurate models. Understanding these changes is essential for the navigation community and for improving the accuracy of geomagnetic field models.