SKY SCIENCE Earth’s Magnetic Field PHYSICS & CHEMISTRY

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EARTH’S MAGNETIC FIELD

By Peter McMahon

Did you know that without proper protection, the Northern Lights (er, at least, their source) could actually be lethal to you. While we’re safe here on Earth, giant flares that blast out from our Sun could fry us like an over-microwaved Pizza Pop, outside our home planet’s magnetic field. Protecting us from harmful solar particles is just one of the favours this handy, invisible donut does for us each and every day…

Mmmm… Giant Space Donuuut…. To get an idea of the shape of Earth’s magnetic field, imagine a kind of un-symmetrical donut: a sort of teardrop-shaped ‘comet-donut,’ stretched a little wider at the sides than the front, and stretched waaaaay more out at the back. Now imagine such a donut so big that it wraps around the Earth and extends outward 5 times Earth’s diameter at the Sun-facing ‘front,’ more than 7 times on each ‘side,’ and as much as 1,000 times at the ‘back’ facing away from the Sun. This giant donut-force-field is real, but invisible…just like the force attracting small metal objects (like iron filings) to a bar or fridge magnet. What Makes Our Magnetic Field? Earth's magnetic field is created mostly by electric currents in its liquid outer core.

           

 

SKY SCIENCE Earth’s Magnetic Field PHYSICS & CHEMISTRY

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That outer core is made of molten iron so hot and under so much pressure that the normally solid metal exists in a liquid state, sort of like molten lava in volcanoes. This material is also highly conductive, allowing great loops of alternating magnetic fields that generate an electric field and, from that – a rotating planet-wide ‘geodynamo’ that forms Earth’s ‘geomagnetic’ shield against harmful particles. Space Weather and Solar Storms

You can’t actually see the earth’s magnetic field. But, you can see its effects. When charged particles erupt like volcanoes near sunspots on the Sun (sunspots are intense magnetic fields on the surface of our local star) they blow away from the Sun in a stream of ions and electrons called “solar wind.” Sometimes, these “solar storms” erupt on a part of the Sun facing Earth. When this happens, scientists use measurements from different aspects of the eruption to guess how the solar storm-front will impact Earth’s atmosphere, its magnetic field, and the technology above and below these regions. Shields Up!

When the eruption’s solar wind — plasma made up of ionized (positively or negatively charged) hydrogen atoms (protons) and electrons — hits the Earth, it’s travelling at hundreds of kilometres per second. The solar wind swirls past our planet’s magnetic fields, setting in motion a sort of atmospheric dynamo. Sometimes that energy makes it all the way into our atmosphere, with electrical currents flowing down into the atmosphere near our North and South Poles. When that happens, and the particles rain down along our magnetic field at the poles in just the right way, they start

up a planet-sized dynamo (an engine, if you will) that leads to the creation of beautiful auroras. “Geoelectromagnetism: The Show” Auroras (which are known in this hemisphere as the Northern Lights) are the visible result of interaction between space weather from the Sun and Earth’s magnetosphere.

           

 

SKY SCIENCE Earth’s Magnetic Field PHYSICS & CHEMISTRY

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For reasons still not fully understood, the particles causing the aurora are accelerated inside the electrical currents flowing in space. At altitudes of several thousand kilometres above the poles, the fast-traveling particles spin down along magnetic field lines into the Earth’s ionosphere (the region in which the International Space Station orbits). Eventually, they can hit the atmosphere and create a visible, dazzling sky-show. Depending on the time and place, auroras can be faint green glows or blazing red, green, pink, yellow, blue and even purple curtains of light rippling in the north. The colours represent different atoms and molecules in a state of excitement. As the atoms and molecules rev-up, then relax, they glow: green and sometimes red for oxygen and blue or pink for nitrogen. Reversal All sorts of ‘doomsday’ theories have predicted that the end of the world will come when Earth’s magnetic field starts to reverse itself, flipping north-for-south and vice-versa.

While many of these ‘apocalypses’ have come and gone without the big flip being observed (including the latest one on December 21, 2012), Earth’s magnetic field does appear to have flipped many times in the past, though not instantly, like the urban myths would have you believe. Geologists have found evidence of this reversal in the magnetic charges left in iron oxides within ancient lava flows and sediment from the bottom of the ocean.

Such reversals (which take thousands of years to start and finish) happen every 100,000 to 50 million years, seemingly at random. The last one happened about 800,000 years ago. However, during reversals the magnetic field does not disappear – but it does change its shape. Fortunately, the changes continue to provide us with a shield from space radiation. Research… and the Future Solar particles can disrupt satellite-based communication and other services – from GPS to television – and even whole power grids: a solar flare in 1989 caused the collapse of Hydro-Québec's entire electricity transmission system.

           

 

SKY SCIENCE Earth’s Magnetic Field PHYSICS & CHEMISTRY

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As a result of those threats, and our close proximity to magnetic north, Canada has become a world-leader in research into space weather and how the fields near Earth help protect us against it. “We want to get to the point where we can deliver accurate space weather forecasts soon enough to be a useful early-warning system,” says Ian Mann, a space physicist at the University of Alberta. Mann is in charge of a nation-wide network of dozens of sensors, cameras, and satellite link-ups. Together with leaders of several other Canadian space projects, along with international partners, the various networks make up the world’s largest space-weather detection effort. Building a “Space Weather Station” in the Arctic Meet Mike Greffen, one of the people behind the installation of the $25 million-dollar Resolute Bay Incoherent Scatter Radar (RISR-C), a hockey-arena-sized array of sensors for studying the inner

edge of Earth’s magnetosphere. “It’s always an adventure up here,” says Greffen during a trip to Resolute Bay, Nunavut, an outpost of 230 people, 300 km north of Baffin Island (farther north from Toronto than the distance between Vancouver, BC and Halifax, NS). Greffen is the program manager for the University of Calgary’s Auroral Imaging Group, led by prominent space physicist Eric Donovan. As Greffen brushes snow off his laptop, the Arctic wind blows across this flat, barren desert. “You fix tiny wires in a magnetometer with a Radio Shack soldering iron…then you turn around to start your

next project and you’re using a chainsaw.” Days before, elements of RISR-C arrived here on an annual cargo ship, which brings in food, supplies, newly-purchased cars, two fishing boats, a house, and everything else the community will receive for the year. Along with two U Calgary staffers and local contractors, Greffen will spend the next three weeks starting to build this facility. As with previous projects, university researchers will rely on locals interested in earning a little extra money to maintain and do repairs on the installation: Out here, there’s no Home Hardware or FedEx. And flights from Greffen’s home base of Calgary can run up to

           

 

SKY SCIENCE Earth’s Magnetic Field PHYSICS & CHEMISTRY

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$8,000. When it’s finished, the RISR-C array could help us learn how to build Global Navigation Satellite Systems that are more likely to withstand major disruptions in the our magnetic field: just another way we’re preparing for future storms from the Sun and their impacts for Earth.

• More on Earth’s magnetic field • Author Peter McMahon’s article on solar wind and the Northern Lights in the Jan 2013 issue of

Canadian Geographic • More on Ian Mann’s space physics network, CARISMA • Aurorawatch monitors geomagnetic activity in the Edmonton area and provides alerts of possible

auroras • More on the RISR-C project and other work Mike Greffen is involved with • More on Canada’s contribution to the global THEMIS project, for which Eric Donovan is the

Canadian lead researcher Images: NASA, Peter McMahon, Ian Mann, and Mike Greffen