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SUN COURSE - SLIDE SHOW 5

SUN COURSE - SLIDE SHOW 5. Introduction,MHD Eqns, Induction eqn, Coronal loops. SUNS POTS. 1. OBSERVATIONS. Existence known since 350 BC (Greece), 28 BC (China). Sunspots. In West, no ref until 850 AD; Galileo (1611). Umbra Penumbra. Site strong B. Flux tube - ?? Model.

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SUN COURSE - SLIDE SHOW 5

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  1. SUN COURSE - SLIDE SHOW 5 Introduction,MHD Eqns, Induction eqn, Coronal loops SUNS POTS

  2. 1. OBSERVATIONS

  3. Existence known since 350 BC (Greece), 28 BC (China) Sunspots In West, no ref until 850 AD; Galileo (1611) Umbra Penumbra Site strong B. Flux tube - ?? Model

  4. Dark because Cool 1600 K cooler than photo. ?? Why cool

  5. LATEST IDEAS on NATURE of SUNSPOTS Introduction Observed over 2000 years Hale (1908): strong B (3000G cf mean q Sun 3 - 20 G) Outside sunspots: strong small-scale convn (gran, 1 Mm) + weak larger-scale convn (supergran, 15 Mm) Umbra - (15 Mm, B strong, vertical) dark -- cool, inhibition of convection

  6. Penumbra (40 Mm, B intermed, inclined) radial light/dark filaments

  7. NEW THEORY - Weiss et al (2004)

  8. StunningImage(Swedish telescope, La Palma) Penumbral structure created by B Close-up of penumbra -> new surprises:

  9. Points moving along lanes; Bright flows in/out; Strange dark cores

  10. 2. SOLAR CYCLE Magnetogram SURPRISES: -- patterns of sunspots -- why ?

  11. Magnetic Field (B) and Plasma Coupled B exerts force on plasma -- move together In interior, plasma dominates --> moves B Rotation shears B --> 2 tubes B --> Emerge:

  12. Magnetic Tube Emerges Creates pair of sunspots +/- Opposite pattern in s. hemisphere

  13. (i) Quiet Sun - Network Global Magnetic Field of Sun At photosphere <|B|> ~ 3 - 20 G, but most is strong (1 kG) & vertical mixed polarity -- at edge of supergranule cells -- covers Sun at s. minimum ephemeral active regions (1019 Mx) -- emerge & migrate to boundary --> network fragments (F = 2x1018 Mx, B = 1 kG) -- at edges of cells internetwork fragments (F = 6x1016 Mx, B = 10-100 G ?) -- inside cells

  14. (ii) ACTIVE REGION FLUX Spreads out --> remnant active region Merges --> unipolar region -- one dominant polarity Migrates to the poles --> polar field • Emerges as • sunspots (B = 3 kG, • flux = 1022 Mx) • * active regions --> faculae (bright)

  15. Solar Cycle Sunspots vary with period 8-15 years (average 11.1 yr) Two zones between -35o and +35o latitude In opposite hemispheres, leading spots have opposite polarities (Hale) Leading polarity is closer to equator (Joy)

  16. New spots emerge at start of cycle at high latitudes w. opposite polarity As cycle progresses, spots form at lower latitudes (Sporer) Polar Fields: * maximum extent at s. minimum * change polarity 1-2 years after s. maximum

  17. No sunspots varies - 11-year cycle Also cycle in X-rays And in shape of corona:

  18. Chromosphere

  19. SOHO (Solar & Heliospheric Observatory) Orbiting Sun at L1 point in phase with Earth Observing Sun continuously for first time

  20. ? Earth Influenced by Solar Variability Number of Sunspots Oscillates w. 11-year Cycle

  21. SURPRISE (1976) Realised NO sunspots in most of 17th centy "Maunder Minimum" -- Little Ice Age So B on Sun affects climate of Earth !! How ??

  22. SOHO --> Total Emission (t) 1996-2000 Emission varies by 0.2% -- passage sunspots Increase by 0.1% from sunspot min to max ? Contribution to global warming

  23. SURPRISE (2001) Discovered that Global B of Sun doubled since 1900 ? Effect on Global T of Earth Observed increase in T (blue) Best estimate of increase caused by Sun (yellow) Only 1/3 global warming (1970 to 2000) caused by Sun ? Mechanism couple Sun/climate

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