Unpredicted and unpredictable behaviour of the Earth’s magnetic core since 2014 has led to an additional release of the Model.
The World Magnetic Model (WMM) is normally produced jointly by the British Geological Survey (BGS) and the US National Oceanic and Atmospheric Administration (NOAA) at 5-yearly intervals. But unusual magnetic activity has caused them to release an unprecedented second edition of the 2015 issue - WMM2015v2.
BGS explains that, having mapped the field changes that have occurred since 2015, they show that they seem to be related to two phenomena:
- an abrupt unpredictable change called a 'geomagnetic jerk' in 2014-15,
- and an acceleration of flow in the core in the northern hemisphere.
This additional update to the WMM will be used until the next release in December 2019, which will be a best estimate of the likely change in the core field until 2025.
All those using compasses or magnetometers - including smart phone users - should ensure that they, or their device, use this latest model of magnetic variation and dip.