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) –Science goals: solar magnetism, variability Helioseismology: global & local –Precursors to erruptions More global simulations –Coupled to exterior (corona, wind, …) 2

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) 3

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

5 What we know about the Sun

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) … 6

15 M Kelvin?  solar neutrino problem : accurate measurements

Input from helioseismology 8

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 Roger Ulrich (1970) Franz-Ludwig Deubner (1974)

11 Degree l, order m

12 GONG global 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 Refraction Reflection Top: reflection when wavenlength ~ density scale height Deeper down: Sound speed large

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

17 What else from helioseismology? spoke-like at equ. d  /dr>0 at bottom d  /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

not 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 20

21 Revised solar abundances

22 In conflict with helioseismology

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

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

29 How deeply seated? Clues from helioseismology:  (r,  ) No cyclic modulation at great depth

30 Sunspot predictions (of 2008)

31 Sunspot predictions (current)

32 Predicting Solar Activity Sunspots Polar Fields Solar Prediction Panel, 2006 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. Theory: Deep circu- lation? The low polar fields at the recent solar minimum predicted a small cycle 24 Sunspots MWO* WSO ?

33 Asymmetric Solar Activity Spots & Groups 18

34 Cycic Maunder mininum: 10 Be record

Brun, Brown, Browning, Miesch, Toomre 35

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

Pencil code Käpylä, Mantere, Brandenburg (2012)

38 Dynamo wave from simulations Kapyla et al (2012)

39 Importance of solar activity

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

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

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

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