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The Sun’s enduring mysteries

The Sun’s enduring mysteries. To prepare for the coming years What we know What we don’t understand What is important Axel Brandenburg ( Nordita , Stockholm ). Coming years?. New satellites (Solar Orbiter, …) Out of ecliptic (like Ulysses) Ground based (ATST)

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The Sun’s enduring mysteries

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  1. The Sun’s enduring mysteries To prepare for the coming years What we know What we don’t understand What is important Axel Brandenburg (Nordita, Stockholm)

  2. Coming years? • New satellites (Solar Orbiter, …) • Out of ecliptic (like Ulysses) • Ground based (ATST) • Science goals: solar magnetism, variability • Helioseismology: global & local • Precursors to erruptions • More global simulations • Coupled to exterior (corona, wind, …)

  3. Monitoring & observing • Solar orbiter: 2017 (ESA/NASA) • (45 R = 0.2 AU, heliosynch, + solar probe) • SDO: 2010 (NASA, geosynch) • Stereo: 2006 (NASA), 2 space crafts • SOHO: 1995 (ESA/NASA) • Ulysses: 1990 (NASA/ESA)

  4. Further reading • M. Stix “Solar Physics” Springer • Wikipedia: … • A. Kosovichev et al. “Triennial report of IAU commission 12” • ADS • search on titles/abstracts

  5. What we know about the Sun

  6. What we understand • Source of energy: nuclear (not thermal) • Internal structure: 15 M Kelvin core temp. • Depth of convection zone • Solar granulation • Solar wind (Parker 1958) • Differential rotation (except details) • Dynamo theory in general • Coronal heating (Parker’s nano flare idea) • …

  7. 15 M Kelvin?  solar neutrino problem 1968: accurate measurements

  8. Input from helioseismology

  9. 5 min oscillations  helioseismology Discovered in 1960 (Leighton et al. 1962) Was thought to be response of upper atmosphere to convection

  10. 5 min osc are global Franz-Ludwig Deubner (1974) Roger Ulrich (1970)

  11. Degree l, order m

  12. GONGglobal oscillation network group Since late 1980ties

  13. Current state of the art SOHO Space craft 1993 – 2014 (lost in 1998)

  14. Only p-modes observed

  15. RefractionReflection Top: reflection when wavenlength ~ density scale height Deeper down: Sound speed large

  16. Inversion: input/output Abel integral eqn Duval law: collapsed kw-diagram Sound speed

  17. What else from helioseismology? spoke-like at equ. dW/dr>0 at bottom dW/dr<0 at top Rigid below CZ

  18. Active region subsurface flows Hindman et al. (2009, ApJ) Ring diagram analysis

  19. Surface flows: granulation Horizontal size L=1 Mm, sound speed 6 km/s Correlation time 5 min = sound travel time Nordlund, Stein, Scharmer, and others

  20. What is not well understood • Unexpected abundence revisions • Mixing beneath convection zone • Spoke-like differential rotation • Location of solar dynamo • What releases coronal mass ejections

  21. Revised solar abundances

  22. In conflict with helioseismology

  23. Overshoot below convection zone • Lithium is primordial • Burns at T > 2.6 M Kelvin • Some distance below CZ: • But why is depletion 1/140 • And not all? Charbonnel et al. (1999) Tschaepe & Rudiger (1999)

  24. Sunspots

  25. Large scale coherence Active regions, bi-polarity systematic east-west orientation opposite in the south

  26. Buoyant rise of flux tubes

  27. Solar 11 year sunspot cycle • Sunspots between +/- 30 degrees around equator: why? • New cycle begins at high latitude • Ends at low latitudes • equatorward migration: why? butterfly diagram

  28. a-effect dynamos (large scale) New loop Differential rotation (faster inside) Cyclonic convection; Buoyant flux tubes Equatorward migration  a-effect

  29. How deeply seated? Clues from helioseismology: W(r,q) No cyclic modulation at great depth

  30. Sunspot predictions (of 2008)

  31. Sunspot predictions (current)

  32. MWO* WSO 21 22 23 Sunspots 24 Predicting Solar Activity WSO Polar Fields Observations and theory suggest that the magnetic field at the poles of the Sun at solar minimum is a good predictor of the next solar cycle. Sunspots ? Theory:Deep circu-lation? The low polar fields at the recent solar minimum predicted a small cycle 24 Solar Prediction Panel, 2006

  33. Asymmetric Solar Activity Spots & Groups 18

  34. Cycic Maunder mininum: 10Be record

  35. Brun, Brown, Browning, Miesch, Toomre

  36. Ghizaru, Charbonneau, Racine, … • Cycle now common! • Activity from bottom of CZ • but at high latitudes

  37. Käpylä, Mantere, Brandenburg (2012) Pencilcode

  38. Dynamo wave from simulations Kapyla et al (2012)

  39. Importance of solar activity

  40. Historic space weather events • 21 Dec 1806 Humbold: erratic compass var. • 1 Sep 1859 Carrington flare: telegraphs disr.

  41. More recent weather events • 2 Aug 1972: life-threatening particle expos. • Apollo 16: 16 Apr 1972 • Apollo 17: 7 Dec 1972 • 13 Mar 1989: Quebec blackout • Aug 1989: halt of all trading in Toronto • Story in New Scientist of 9 Sept • Now routinely rerouting transpolar routes

  42. Need a holistic approach Warnecke, Brandenburg, Mitra (2011, A&A, 534, A11)

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