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On the Scene

Earth's magnetic field ... updated

Three most used models of Earth's magnetic field are revised to reflect small changes in the field

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The strength and direction of Earth’s magnetic field is slightly yet constantly changing. This phenomenon is a boon for researchers: Geologists can use knowledge of past variations in the field over geologic time to help determine when certain minerals — ones that preserve a record of that field — were formed. Similarly, archaeologists can use knowledge of recent changes in the field to estimate the age of artifacts that happen to have recorded the direction of Earth's magnetic field.

A changing magnetic field, however, is a hindrance for people using that field to navigate over long distances, where even a small error in direction can be result in a big miss, says Stefan Maus, a geophysicist at NOAA’s National Geophysical Data Center in Boulder, Colo. Examples include the obvious, such as intercontinental jet travel, and the not-so-obvious, such as using high-tech drilling equipment to aim for a small pocket of petroleum or natural gas that lies a few kilometers away from a drilling platform.

So, once every five years Maus and his colleagues update the three commonly used models of Earth’s magnetic field — the International Geomagnetic Reference Field (IGRF), the World Magnetic Model (WMM) and the Enhanced Magnetic Model (EMM). These models vary in their resolutions and in the computing power needed to run them, says Maus, but all enable the same thing: Input your location, and the model — like a high-tech compass — tells you the direction of Earth’s magnetic field there.

One of the models, the World Magnetic Model, is small enough to run on smartphones such as Google’s Android phone. Here’s how it typically works: The phone uses data from the Global Positioning System to determine its location, then passes that data to the WMM. Then, for that location, the model calculates the angular difference between the nearest magnetic pole and the true, geographic pole (an angle known as the declination). Finally, software takes data from the phone’s magnetic sensors, takes the declination into account, and then displays true north. And voila! You’re no longer lost in the woods.

Updates to all three models will come out in the next few weeks, but the new version of the World Magnetic Model has been released, Maus reports.

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