SKY SCIENCE
Earth’s Magnetic Field
PHYSICS & CHEMISTRY
BACKGROUNDER
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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 ‘cometdonut,’ 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.
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SKY SCIENCE
Earth’s Magnetic Field
PHYSICS & CHEMISTRY
BACKGROUNDER
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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.
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Earth’s Magnetic Field
PHYSICS & CHEMISTRY
BACKGROUNDER
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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.
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Earth’s Magnetic Field
PHYSICS & CHEMISTRY
BACKGROUNDER
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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 (RISRC), 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
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Earth’s Magnetic Field
PHYSICS & CHEMISTRY
BACKGROUNDER
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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.
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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
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