Space Weather

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Space Weather
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Coronal loops Intense magnetic field lines trap
plasma
http//www.nasa.gov/centers/goddard/images/content
203911main_TRACE_loop_arcade_lg.jpg
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Coronal mass ejection Explosive ejection of gas
and plasma from the sun
A space hazard
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Normal conditions Typical concentration of
particles near Earths 1 particle / cm3 Typical
velocity 400 km/sec
(Protons)
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During a solar flare, particle flux increases by
a factor gt 100,000
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Ionized radiation is bad for you
Sievert measure of radiation energy absorbed
(in gamma ray equivalent) (joules per kg)
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Ionized radiation is bad for you
Solar Flare
Multiply rem x 10 to get mSv
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Fukashima Reactor 1 500 uSv/hr
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Interaction of the solar wind and Earths
magnetic field All else being equal, this is
what the Earths field would look like from far
away
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But the solar wind cannot cross fields lines, so
what happens?
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Bow shock where velocity of solar wind drops
sharply as it approaches the magnetopause Magnetop
ause delimits boundary between solar wind and
Earths magnetosphere. Magnetosheath region
between the bow shock and the magnetopause Outsid
e the bow shock the solar wind wins, Inside the
magnetopause the Earths field wins, in between
is a messy competition
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http//science.nasa.gov/
The polar auroral fountain sprays ions - oxygen,
helium, and hydrogen - from Earth's upper
ionosphere into deep space. The loss is
miniscule compared to the immense ocean of air
covering our world, but is significant in terms
of what drives space weather around our world.
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The magnetic conditions inside and outside the
Earths magnetosphere are very different
Much quieter inside
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Generation of a current sheet in the
magneto-tail. Occurs where the magnetic field
switches from south to north, and the field lines
are stretched out by the solar wind
Circles show the sense of the magnetic field
around parallel wires (with current into page).
For a sheet of current, the magnetic field
Would be given by the red and green lines.
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The solar current sheet (or magnetic equator)
Controlled by off-axis dipole, and 27 day solar
rotation. Magnetic equator precesses from Earth
it appears to oscillate up and down
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Some small amount of charged particles can enter
magnetopause where field lines and particle
trajectories are most nearly parallel
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Go to notes on electron orbits in magnetic
fields.
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Aurora Borealis (northern lights)
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From space
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Van Allen radiation belts
Outer belt 4 to 5 Re, electrons Inner belt
0.01 to 1.5 Re, protons, a particles
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1800
180
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mSv/hour
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1 hour in Van Allen Belt
Multiply rem x 10 to get mSv
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The South Atlantic Anomaly
SAA is the closest approach of Van Allen
radiation belt to the surface. Happens b/c
magnetic pole is tilted relative to Earths axis,
and b/c Earths magnetic field is not uniform If
you are an astronaut or a satellite you want to
avoid the area (Hubble shuts down). SAA is
drifting westward 0.3o per year
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Magnetic fields on other planets.
Saturn sometimes sits within Jupiters
magnetosphere
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Jupiters radiation belt
(Jupiters magnetotail extends beyond Saturn)
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Aurora on Jupiter
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Jupiters northern lights
Io is a major source of plasma- Sulphur dioxides
photo dissociates
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Saturn too