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Earth's Magnetic Field Is Acting Up and Geologists Don't Know Why (nature.com)
schwit1 quotes Nature:
Something strange is going on at the top of the world. Earth's north magnetic pole has been skittering away from Canada and towards Siberia, driven by liquid iron sloshing within the planet's core. The magnetic pole is moving so quickly that it has forced the world's geomagnetism experts into a rare move. [T]hey are set to update the World Magnetic Model, which describes the planet's magnetic field and underlies all modern navigation, from the systems that steer ships at sea to Google Maps on smartphones. The most recent version of the model came out in 2015 and was supposed to last until 2020 -- but the magnetic field is changing so rapidly that researchers have to fix the model now.
"The error is increasing all the time," says Arnaud Chulliat, a geomagnetist at the University of Colorado Boulder and the National Oceanic and Atmospheric Administration's (NOAA's) National Centers for Environmental Information.... By early 2018, the World Magnetic Model was in trouble. Researchers from NOAA and the British Geological Survey in Edinburgh had been doing their annual check of how well the model was capturing all the variations in Earth's magnetic field. They realized that it was so inaccurate that it was about to exceed the acceptable limit for navigational errors.
Nature's article was updated on January 9th to inform readers that the release of the corrected World Magnetic Model, which should restore accuracy through the end of 2019, has now been postponed from January 15th to January 30th -- "due to the ongoing US government shutdown."
"The error is increasing all the time," says Arnaud Chulliat, a geomagnetist at the University of Colorado Boulder and the National Oceanic and Atmospheric Administration's (NOAA's) National Centers for Environmental Information.... By early 2018, the World Magnetic Model was in trouble. Researchers from NOAA and the British Geological Survey in Edinburgh had been doing their annual check of how well the model was capturing all the variations in Earth's magnetic field. They realized that it was so inaccurate that it was about to exceed the acceptable limit for navigational errors.
Nature's article was updated on January 9th to inform readers that the release of the corrected World Magnetic Model, which should restore accuracy through the end of 2019, has now been postponed from January 15th to January 30th -- "due to the ongoing US government shutdown."
Declination needs to be changed every year by serious navigators. More often near the poles. This has been true since before any slashdot reader was born.
The magnetic shift is increasing in complexity and rate of change. This has also been known for a very long time.
We are overdue for a pole shift given our current understanding of the magnetosphere. We might be lucky enough to witness multiple north and south poles, followed by a rapid reversal where every magnetic compass in the world will point the wrong way.
Datum transformation is and will be an ongoing headache for map makers.
In the cited situation - the World Magnetic Model does contain a component intended to compensate the geomagnetic field changes, The component must not be tracking reality well enough.
The differences between GDA and WGS84 come from a different source. GDA moves with the Australia, while WGS84 moves with IERS Reference Meridian, 5.3 arc seconds or 102 metres (335 ft) east of the Greenwich meridian at the latitude of the Royal Observatory.
The Geocentric Datum of Australia (GDA94) was the official geodetic datum before GDA2020. It was adopted nationally in January 2000. GDA94 replaced the Australian Geodetic Datum 1966 (AGD66) and Australian Geodetic Datum 1984 (AGD84). The standard map projection associated with GDA94 is the Map Grid of Australia 1994 (MGA94), a transverse Mercator projection that conforms to the internationally accepted Universal Transverse Mercator Grid system.
GDA94 is a coordinate reference system whose origin coincides with a determination of the centre of mass of the earth, hence the term ‘geocentric’. GDA94 is a ‘plate-fixed’ or ‘static’ coordinate datum based on the International Terrestrial Reference Frame 1992 (ITRF92), held at the reference epoch of 1 January 1994.
The fact that the magnetic field is moving is not news. The problem is that it's moving unpredictably.
The two major geomegnetic field models (the World Magnetic Model and the International Geomagnetic Reference Field) have long included time-varying terms. These predict the magnetic field shape (to about 10th order spherical harmonics, not just the pole location!) for the five years between releases.
Both released a model in 2015, which was expected to be good until the next release in 2020. But the field has not done as the 2015 WMM predicted, so they're making a 2019 release