Space Weather

1. Space Weather

2. Coronal loops Intense magnetic field lines trap plasma http://www.nasa.gov/centers/goddard/images/content 203911main_TRACE_loop_arcade_lg.jpg

3. Coronal mass ejection Explosive ejection of gas and plasma from the sun A space hazard…

4. Normal conditions Typical concentration of particles near Earths ~1 particle / cm3 Typical velocity ~400 km/sec; (Protons)

5. During a solar flare, particle flux increases by a factor > 100,000

6. Ionized radiation is bad for you… Sievert – measure of radiation energy absorbed (in gamma ray equivalent) (joules per kg)

7. Ionized radiation is bad for you… Solar Flare Multiply rem x 10 to get mSv

8. The atmosphere protects us from the solar flares 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 Fukashima Reactor #1 500 uSv/hr

9. Interaction of the solar wind and Earth’s magnetic field All else being equal, this is what the Earth’s field would look like from far away

10. But the solar wind cannot cross fields lines, so what happens?

11. Bow shock – where velocity of solar wind drops sharply as it approaches the magnetopause Magnetopause – delimits boundary between solar wind and Earth’s magnetosphere. Magnetosheath – region between the bow shock and the magnetopause Outside the bow shock the solar wind wins, Inside the magnetopause the Earth’s field wins, in between is a messy competition

12. The magnetic conditions inside and outside the Earth’s magnetosphere are very different Outside Inside Much quieter inside

13. 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.

14. 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

15. Some small amount of charged particles can enter magnetopause where field lines and particle trajectories are most nearly parallel

16. Go to notes on electron orbits in magnetic fields….

18. Aurora Borealis (northern lights)

19. From space

22. Van Allen radiation belts Outer belt: 4 to 5 Re, electrons Inner belt: 0.01 to 1.5 Re, protons, a particles

23. 1800 180 18 mSv/hour

24. 1 hour in Van Allen Belt Multiply rem x 10 to get mSv

25. 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 Earth’s axis, and b/c Earth’s 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

26. Magnetic fields on other planets…. Saturn sometimes sits within Jupiter’s magnetosphere

27. Jupiter’s radiation belt (Jupiter’s magnetotail extends beyond Saturn)

28. Aurora on Jupiter

29. Jupiter’s northern lights Io is a major source of plasma- Sulphur dioxides photo dissociates…

30. Saturn too…