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The Sun’s enduring mysteries

Delve into the enigmatic nature of the Sun, exploring what we know and what remains a mystery. Discover the significance of solar magnetism, variability, and the complex dynamics of the solar system. Learn about groundbreaking discoveries in helioseismology, solar wind, and global simulations, and the implications for predicting solar activity. Gain insights into the deep-seated mysteries of sunspots, differential rotation, and the solar dynamo. Explore the history of major solar events and their impact on Earth. Prepare for the coming years with new satellites and advancements in solar science.

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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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