字幕表 動画を再生する 英語字幕をプリント The Earth's magnetic north pole is shifting, and I mean that in two ways. One, it's literally moving away from Canada and towards Siberia, and two, it's accelerating. It's moving so fast now we've had to update our models of Earth's magnetic field ahead of schedule. Why our magnetic poles move and flip has always been something of a mystery, but now a team of researchers from Leeds University believe they've found the culprit: blobs. Since the magnetic north pole was discovered in the 1830s, it's been moving. Slowly at first, notching a top speed of at most 15 kilometers per year. But since the 1990s that pace has picked up, and now it trucks across the arctic anywhere from 50 to 60 kilometers per year. I should mention that things can get a little confusing when we start to talk about “north poles.” The earth actually has several, depending on your definition. There's the geographic north pole, where all lines of longitude we've drawn on a globe converge. The magnetic north poles don't align with the geographic north pole. And yes I said “poles,” because it turns out there are multiple magnetic north poles. You've probably seen earth's magnetic field likened to a giant bar magnet in your textbooks, with one north and one south pole, what's known as a dipole. From a zoomed out view, like say in space, the earth's magnetic field appears to look and act like a dipole, and the spot that best represents the northern dipole is off the coast of Greenland. However, on a finer scale the earth's magnetic field is more varied and complex than a giant bar magnet, and there is a point where the earth's magnetic field is perpendicular to Earth's surface. If you were to stand over it with a compass, the needle would try and point straight down, so it's called the dip pole. So to recap there is a geomagnetic north dipole and a magnetic north dip pole and they are different things that are in different places. Got it? Great, moving on. Anyway the dip pole is the one that's on the move, and we think it's because of the movement of the liquid iron in earth's outer core. A few years ago, the researchers from Leeds suggested that jet streams of molten iron were the culprit, but the idea was scrapped because the jets started accelerating years after the pole's movement did. So the scientists have turned their attention farther south to find the source of the movement. The team from Leeds used 20 years of data collected by satellites, including European Space Agency's Swarm, a trio in polar orbits that measure the strength and direction of earth's magnetic field. They concluded that changes in flow at lower latitudes in the outer core have changed the magnetic flux, or the number of field lines, in two blobby areas. These blobs of magnetic flux are located underneath Canada and Siberia. While Canada's blob has gotten weaker, Siberia's has gotten stronger. This means Russia is winning the magnetic tug-of-war, and based on the team's models it will continue to do so for at least a few more decades. But the balance is fairly delicate, so a small change in the field could send the dip pole back Canada's way. Wherever it goes, it's important we keep tabs on it because its position is used to update the World Magnetic Model, something used by all navigation systems that rely on the geomagnetic field. The World Magnetic Model is necessary to correct for local compass errors, and is used by the U.S. Department of Defense, the U.K.'s Ministry of Defence, NATO, and even average everyday smartphone users like you and me. We update the model every 5 years, and actually updated it ahead of schedule because the dip pole is dipping out so fast. Still, the next time I'm late for something because my GPS took me on a weird route, I'm going to blame the blobs and hope my boss buys it. As if the whole multiple north poles bit weren't confusing enough, the magnetic north dip pole is technically a magnetic south pole. Think about it, why else would it attract the north pole of your compass? To learn more about what's happening inside Earth's core and why our magnetic fields are moving, check out Maren's video here. Make sure to subscribe to Seeker to stay up to date on your magnetic field news. Thanks for watching and I'll see you next time.