To find your way using a magnetic\ud compass with a map, you need to know\ud the difference between magnetic north\ud and map north. This difference is called\ud ‘grid magnetic angle’, and in the UK it is\ud derived from a model of the Earth’s magnetic\ud field, which is updated every year. The variation\ud To go north, you just follow your compass towards magnetic\ud north, right? Not quite. Geophysicists have to work hard so\ud we can continue to navigate with map and compass. Susan\ud Macmillan and Tom Shanahan describe how the UK magnetic\ud repeat station network helps.\ud in grid magnetic angle reflects changes in the\ud Earth’s magnetic field arising from sources\ud in the Earth’s fluid outer core. We don’t yet\ud understand these changes well enough to make\ud good forecasts, so we need to monitor them\ud continuously
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