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Long Term Movement of the North Magnetic Pole Introduction
The accompanying figure shows the path of the North Magnetic Pole since its discovery in 1831 to the last observed position in 2001. During the last century the Pole has moved a remarkable 1100 km. What is more, since about 1970 the NMP has accelerated and is now moving at more than 40 km per year. If the NMP maintains its present speed and direction it will reach Siberia in about 50 years. Such an extrapolation is, however, tenuous. It is quite possible that the Pole will veer from its present course, and it is also possible that the pole will slow down sometime in the next half century.
The strength and direction of the Earth's magnetic field slowly change with time – a phenomenon referred to as secular change or secular variation. The cause of secular variation is related to the process by which the magnetic field is generated. Secular change occurs everywhere on Earth, but the magnitude of the change varies from place to place and also with time.
The magnetic field in the region of North Magnetic Pole experiences secular variation just like the magnetic field at any other location on the Earth's surface. To illustrate how this leads to the movement of the Magnetic Pole, consider Observer A , standing at the North Magnetic Pole on January 1. On that day he observes that the inclination is exactly 90°, as expected. Repeat observations made at exactly the same spot during the year show that the inclination is slowly decreasing. On January 1 of the following year he observes an inclination of 89° 57'. During the same time interval, Observer B, who is standing 40 km northwest of Observer A notices that the inclination has increased to 90°. He is now at the North Magnetic Pole. So the slow motion of the Magnetic Pole across the Arctic is due to the secular variation of the magnetic field, a process that originates in the outer core of the Earth, approximately 3000 km below the surface. |
