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Space Weather. Coronal loops Intense magnetic field lines trap plasma 203911main_TRACE_loop_arcade_lg.jpg

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  • Slide 1
  • Space Weather
  • Slide 2
  • Coronal loops Intense magnetic field lines trap plasma 203911main_TRACE_loop_arcade_lg.jpg
  • Slide 3
  • 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 > 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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  • Multiply rem x 10 to get mSv Solar Flare Ionized radiation is bad for you
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  • 10 km 20 km Mostly, it is the mass of the atmosphere that shields us from solar wind radiation, but the magnetic field helps too The atmosphere protects us from the solar flares Fukashima Reactor #1 500 uSv/hr
  • Slide 9
  • 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?
  • Slide 11
  • Bow shock where velocity of solar wind drops sharply as it approaches the magnetopause Magnetopause delimits boundary between solar wind and Earths magnetosphere. Magnetosheath region between the bow shock and the magnetopause Outside the bow shock the solar wind wins, Inside the magnetopause the Earths field wins, in between is a messy competition
  • Slide 12
  • 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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  • Outside Inside 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.
  • Slide 15
  • 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, particles
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  • 1800 180 18 mSv/hour
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  • Multiply rem x 10 to get mSv 1 hour in Van Allen Belt
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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 ~0.3 o 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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  • Io is a major source of plasma- Sulphur dioxides photo dissociates Jupiters northern lights
  • Slide 31
  • Saturn too

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