WMM2020 continues to be an accurate model of Earth’s magnetic field
Last month saw the publication of the 2023 State of the Geomagnetic Field Report. The report details the current state of Earth’s main magnetic field, and provides a performance analysis of the most recent version of the World Magnetic Model (WMM) released in late 2019, known as WMM2020. Comparisons between the predictions of WMM2020 and recent data collected from the European Space Agency (ESA)’s Swarm satellites indicate that the former can still be considered an accurate model.
Most of our planet’s magnetism originates from the shifting of electrically charged molten metals in its outer core, the behavior of which is unpredictable. An example of the secular changes that these metals can cause is the slow drifting of Earth’s magnetic north pole towards Siberia, a process that has been occurring continuously for the past few decades. As the WMM is predictive in nature, it becomes less accurate over time and must be updated with the newest projections derived from more recently collected data. Updates are scheduled to occur every five years.
The WMM is a joint project between the National Centers for Environmental Information (NCEI) and the British Geological Survey (BGS). It is utilized by these agencies’ respective governments for their navigation, attitude, and heading software. In terms of military applications, the WMM proves indispensable for undersea and aircraft navigation as well as parachute deployment, antenna tracking, iceberg drift determination, and many other activities. In the private sector, the model can be found in virtually every smartphone. The commercial airline industry also uses it to rename airport runways so that they accurately reflect their magnetic heading to allow for greater clarity during landing procedures.
Compared to previous iterations, this year’s report contains more extensive discussions of the two magnetic poles and their drift speeds. Over the past four years, the northern magnetic pole has been traveling at a much faster rate than the southern pole with their average drift speeds measuring 41 km/year and 9 km/year, respectively. The actual locations and drift speeds of the magnetic poles proved to be very close to those predicted by WMM2020, lending further credence to the overall accuracy of the model itself.
The South Atlantic Anomaly Grows
Also described in the State of the Geomagnetic Field Report is the deepening of the South Atlantic Anomaly (SAA), an area spanning the South Atlantic Ocean and South America where the Earth’s magnetism is weakest. This area is known to cause radiation damage to satellites and problems with radio propagation, issues that are exacerbated by the SAA’s growth in size by seven percent over the past four years. NCEI continues to monitor the situation closely.
A well-known limitation of the WMM is the tendency for its accuracy to drop during magnetic storms, of which there were three that were strong to severe in the past year. These space weather events can cause disparities between actual magnetic declination and the estimated declination provided by the WMM that are temporarily greater than the model uncertainty, especially at high latitudes. Such disparities can potentially affect WMM2020-assisted navigation that relies on the model’s declination estimates. This year’s report includes descriptions of the three storms in order to alert users to this limitation to the WMM. An increase in space weather events is expected for the remainder of the 25th and current solar cycle, which began in 2019 and will last until around 2030. Fortunately, the model takes space weather into account in its error estimates.
Regardless of these minor concerns, all data gathered for the annual report indicates that the WMM2020 is still operating well below the margin of error stipulated by the U.S. Department of Defense. The model can thus continue to be relied on by all technology that implements it.
