What does tracking the North pole have to do with your everyday? More than you’d think! Dr Will Brown of the BGS Geomagnetism Team explains…
It’s been an unusually eventful year for geomagnetism. We began 2019 with the release of an out-of-cycle update to the World Magnetic Model (WMM), observed for the second time in recorded history as the agonic line of zero declination passed through the Greenwich meridian, and finished the year with the release of a new WMM and International Geomagnetic Reference Field (IGRF).
Usually produced every 5 years, the WMM describes the primary component of Earth’s magnetic field, which comes from the motions of liquid iron-rich fluid in the outer core. It is the result of a collaboration between the British Geological Survey and the US’ National Atmospheric and Oceanic Administration’s National Centers for Environmental Information (NOAA/NCEI). The model must be kept up-to-date because the Earth’s magnetic field is slowly but constantly changing, as you can see from the map above. To accommodate this, the WMM also includes a prediction of the magnetic field change for the next 5 years.
One aspect of models such as the WMM, is that they allow us to estimate the location of the Earth’s magnetic dip poles, the points where the magnetic field is vertical, and geomagnetic poles, the points where the axis of a best fitting dipole would meet the surface. If you need a quick refresher on the different types of pole and their locations, see here.
The recent changes of the field have been of particular interest at high northern latitudes, as since the 1990s the motion of the north magnetic dip pole has accelerated more quickly than at any point the last 400 years. According to the new WMM, we are now expecting to see a deceleration of this motion over the next 5 years, but the pole is still moving at roughly 50km per year. In contrast, the southern dip pole, near Antarctica, has moved relatively little in the past few hundred years.
The map shows modelled locations of the north dip pole (red) and geomagnetic pole (blue) since 1900 (according to IGRF-12) and projected for the next 5 years, from 2020 to 2025 (according to the new WMM). Grey contours show each 1000 nano-Tesla band of the horizontal field intensity, with the dip pole located at its minimum. The dashed grey contour line at 2000 nano-Tesla indicates the region beyond which declination is a very unreliable measure of direction, as the field is close to vertical. The insert globe shows the location of the main map with a black box, over contours each 5 degrees of declination. Red contours are eastwards declination, blue are westward, and the green line is the agonic, or zero contour line of declination, which will move westward across the UK over the next 5 years.
The main use of the WMM however, is to provide a magnetic navigation reference model. The WMM is the standard magnetic model used for navigation by organisations such as NATO, the UK Ministry of Defense, and the US Department of Defense, and also by smartphone operating systems such as Android and iOS. The WMM allows us to convert a measurement of the magnetic field, perhaps made by your smartphone, into practical directional information. This is done in much the same manner as you would convert a compass bearing to a map heading. Technology from planes to cars, smartphones to drills for hydrocarbon exploration rely on the WMM behind the scenes, and many of us use it every day without ever realising!
Due to the unpredictable nature of magnetic field changes, BGS and NOAA/NCEI will continue to track the performance of the new WMM until the next update, due in 2025.
Notes:
The open source M_map software was used in part to produce maps included here.
Pawlowicz, R., 2019. "M_Map: A mapping package for MATLAB", version 1.4k, [Computer software], available online at www.eoas.ubc.ca/~rich/map.html
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| The forecast pole position for the next five years |
It’s been an unusually eventful year for geomagnetism. We began 2019 with the release of an out-of-cycle update to the World Magnetic Model (WMM), observed for the second time in recorded history as the agonic line of zero declination passed through the Greenwich meridian, and finished the year with the release of a new WMM and International Geomagnetic Reference Field (IGRF).
Usually produced every 5 years, the WMM describes the primary component of Earth’s magnetic field, which comes from the motions of liquid iron-rich fluid in the outer core. It is the result of a collaboration between the British Geological Survey and the US’ National Atmospheric and Oceanic Administration’s National Centers for Environmental Information (NOAA/NCEI). The model must be kept up-to-date because the Earth’s magnetic field is slowly but constantly changing, as you can see from the map above. To accommodate this, the WMM also includes a prediction of the magnetic field change for the next 5 years.
One aspect of models such as the WMM, is that they allow us to estimate the location of the Earth’s magnetic dip poles, the points where the magnetic field is vertical, and geomagnetic poles, the points where the axis of a best fitting dipole would meet the surface. If you need a quick refresher on the different types of pole and their locations, see here.
The recent changes of the field have been of particular interest at high northern latitudes, as since the 1990s the motion of the north magnetic dip pole has accelerated more quickly than at any point the last 400 years. According to the new WMM, we are now expecting to see a deceleration of this motion over the next 5 years, but the pole is still moving at roughly 50km per year. In contrast, the southern dip pole, near Antarctica, has moved relatively little in the past few hundred years.
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| A GIF of the forecast pole prediction |
The map shows modelled locations of the north dip pole (red) and geomagnetic pole (blue) since 1900 (according to IGRF-12) and projected for the next 5 years, from 2020 to 2025 (according to the new WMM). Grey contours show each 1000 nano-Tesla band of the horizontal field intensity, with the dip pole located at its minimum. The dashed grey contour line at 2000 nano-Tesla indicates the region beyond which declination is a very unreliable measure of direction, as the field is close to vertical. The insert globe shows the location of the main map with a black box, over contours each 5 degrees of declination. Red contours are eastwards declination, blue are westward, and the green line is the agonic, or zero contour line of declination, which will move westward across the UK over the next 5 years.
The main use of the WMM however, is to provide a magnetic navigation reference model. The WMM is the standard magnetic model used for navigation by organisations such as NATO, the UK Ministry of Defense, and the US Department of Defense, and also by smartphone operating systems such as Android and iOS. The WMM allows us to convert a measurement of the magnetic field, perhaps made by your smartphone, into practical directional information. This is done in much the same manner as you would convert a compass bearing to a map heading. Technology from planes to cars, smartphones to drills for hydrocarbon exploration rely on the WMM behind the scenes, and many of us use it every day without ever realising!
Due to the unpredictable nature of magnetic field changes, BGS and NOAA/NCEI will continue to track the performance of the new WMM until the next update, due in 2025.
Notes:
The open source M_map software was used in part to produce maps included here.
Pawlowicz, R., 2019. "M_Map: A mapping package for MATLAB", version 1.4k, [Computer software], available online at www.eoas.ubc.ca/~rich/map.html
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