Space Weather and Plasma Physics: An Introduction

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Space Weather and Plasma Physics An
Introduction
Mark Engebretson, Augsburg College Minnesota
Astronomy Society October 1, 2009
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The idea that we live at the bottom of an ocean
of air was first suggested in 1643 by Torricelli,
a student of Galileo. His idea was supported
by Blaise Pascal, who took a barometer up a
mountain in central France in 1647. Hot air
balloons confirmed that our atmosphere became
thinner and cooler as one went up in altitude.
Airplanes, and then early rockets,
progressively reached toward the edge of
space.Surprisingly, above 60 miles (100 km)
altitude, things became much, much hotter.
Why???
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The first U. S. satellite, Explorer I, brought a
surprise. At least in some locations, space was
filled with radiation enough to overwhelm a
Geiger Counter.
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The Magnetosphere
Later satellites found that far above the
atmosphere is a volume given shape by Earths
magnetic field the magnetosphere.
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The solar wind (moving at 1 million miles per
hour) pushes it back to form a comet-shaped tail.
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A Cartoon View of Space Weather
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Our Sun is a Variable Star
Coronal holes appear as dark areas in ultraviolet
and x-ray images of the Sun. A high-speed solar
wind stream flowing from such a hole, or from a
coronal mass ejection, can buffet Earth's
magnetosphere and trigger auroral displays.
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Coronal Mass Ejections Crossing the Earths
Path
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In space, blasts of solar wind caused by solar
storms would kill any space traveler unfortunate
enough to get caught in them, unless heavily
shielded. Fortunately for life on Earth, the
Earths magnetic field extends far into space
(the magnetosphere) and interacts with the solar
wind. The magnetic field deflects most of these
charged particles away from Earth.
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The few particles that remain headed toward
Earth collide with gas molecules. This generates
the hauntingly colorful phenomena of the auroras
(the northern lights, or aurora borealis, and the
southern lights, or aurora australis. The
ionization of molecular nitrogen emits radiation
at wavelengths corresponding to the visible red
and blue electromagnetic spectrum, and the
ionization of oxygen emits wavelengths visible as
green.
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When do we see the Aurora, and why?
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From the vantage point of the space shuttle, the
auroras lower border near 100 km altitude is
visible.
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Viewed from Above, the Aurora form a Continuous
Oval Around the Poles
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The Aurora are Dynamic
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The Size of the Auroral Oval Changes
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The Earths Dipole Magnetic Field Extends into
Space
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The Magnetosphere is Formed from the Interaction
with the Solar Wind
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The Magnetosphere is Dynamic
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Magnetospheric and Solar Dynamics have Real
Impacts!
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All Planets that have Magnetic Fields have
Magnetospheres
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The Size of the Magnetosphere is Related to the
Strength of the Planetary Field
Mercury
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Even the Sun has a Magnetosphere Called the
Heliosphere
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The Sun has an Eleven-year Cycle of Activity
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Sunspot cycle 24 is surprisingly late and weak. A
few spots appeared just this past week, however.
SOHO X-rays
Visible light
Sept. 30, 2009
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Studying Our Space Environment
The matter that makes up Earths space
environment is plasma, or ionized gas. Plasma,
which occurs only at high temperatures, is much
more common throughout the universe than are the
other states of matter, gas, liquid, and solid.
The only kind of plasma humans can safely
encounter, however, is a candle flame.
Plasmas are more complex than ordinary gases,
because they contain both positively and
negatively charged objects as well as neutral
ones. Because many of the particles in a plasma
are electrically charged, they respond strongly
to electric and magnetic fields, both
individually and collectively.
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Earths Magnetic Field Traps Charged Particles
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The Radiation Belts
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The mix of neutral and charged particles makes
the behavior of plasmas very complex. For
example, ordinary gases support one kind of wave
motion sound. Plasmas support at least 12
kinds of wave motion and many of these involve
waving magnetic fields. The existence of the
electron radiation belts shows that Earths
magnetosphere acts like a giant, natural particle
accelerator. How it works is an area of active
research, and waves seem to intimately involved
with that energization. Our research group at
Augsburg studies the two lowest-frequency kinds
of wave motion, both of which involve magnetic
fields. We look for waves in the magnetic
fields measured by both satellites and
ground-based instruments.
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Magnetometers
Many processes in the magnetospheric and
ionospheric plasma make, and/or are communicated
by, Alfven waves, which travel along magnetic
field lines in a plasma. These waves can be
observed locally by satellites but there are
very few satellites! Once such waves reach the
bottom of the plasma region (the bottom of the
ionosphere), they are usually converted into
electromagnetic waves, which can reach the
ground. Ground magnetometers can be installed
and operated at a fraction of the cost of a
single satellite but of course they only
provide a remote view of the signals that can
actually reach the ground. By deploying many
ground instruments, we can understand the context
within which the few satellites make their
detailed, local measurements.
SATELLITE VIDEO
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Satellites in Space see Waves
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Ground Observatories see Waves, too
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Waves Intensify and Rise in Frequency when an
Interplanetary Shock Wave Arrives
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Worldwide Magnetometer Arrays
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Antarctica -- including the South Pole
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Augsburgs Array in Arctic Canada MACCS
(Magnetometer Array for Cusp and Cleft Studies)
http//space.augsburg.edu
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The MACCS magnetometer at Clyde River, Baffin
Island, Canada
The Airport terminal building
The magnetometer sensor
The sensor box and terminal
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Igloolik
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Pangnirtung
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What do we do with all this data?
Space physics is in some ways like meteorology
(weather), rather than like lab science. We have
to wait for interesting things to happen we
cant turn on a magnetic storm, or usually even
a plasma wave. So, first we look for interesting
events something that is either new, or
familiar but still not explained. We then often
look for more of these events, so we can
determine occurrence patterns or event
characteristics. We then select a few
examples, and often a large sample of events that
we can use for a statistical study. Ill
end with three of the more interesting wave
examples weve seen recently
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Multiple Harmonics Cluster Satellites
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Triggered rising tones Cluster satellites
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Pearl or fish scale waves Halley,
Antarctica