Evolution of the Large-Scale Magnetic Field Over Three Solar Cycles

1. Evolution of the Large-Scale Magnetic Field OverThree Solar Cycles Todd Hoeksema

2. Evolution of the Large-Scale Magnetic Field OverThree Solar Cycles Global Properties Corona & Heliosphere Zonal Magnetic Field Toroidal Magnetic Field

3. Daily Solar Mean Magnetic Field – Sun as a Star 3 Cycles – 1976 - 2009 Rotation Modulation Observed At < 10 uT WSO Sensitivity Issues in ~2001

4. 4 Solar Minima, 3 Polar Reversals 1976 - 2009 South stronger In Cycles 21 + 22 Surge Arrival WSO Large-scale Polar Aperture 55 to Pole

5. MDI Measured Polar Field during Cycle 23 1996-2008 Smaller 75+ Polar Field Is More Symmetric & Reverses Later Difference in Strength is Significant, but Smaller Movie shows observed and Interpolated polar field above 62

6. Axial, Equatorial, and Total Solar Dipole – 3 Cycles 1976 -2009 Total Axial Equatorial

7. The Computed Coronal Field & HCS During Cycle 23 1996-2009 Every 10th Rotation Each panel 2 Rots wide Reversal in 1999-2000 Stable Structures Dipole and Quadrupole Dominate

8. 3 Cycles of the Computed HCS Inclination

9. Ulysses Observed Different Solar Wind Structure During Solar Minimum in 1996 compared with 2008 Low-latitude is more complex and wider due to Decreased importance of Polar Coronal Holes Note: Coronal snapshot useful, but may mislead since structure reflects rotation From McComas et al., GRL 2008 Thanks to J. Luhmann

10. IMF Measured at L1 is Significantly Weaker this Minimum than the Previous Three Ulysses also saw low IMF at high heliolatitudes in 2007 (Smith et al., GRL, 2008) –OMNI data from NSSDC IMF observed to be uniform at all latitudes away from HCS Thanks to J. Luhmann

11. Computed open flux foot points – Coronal Hole Proxy Each Panel shows ~10 years starting 1972. Low latitude holes are relatively more important during this solar minimum 1973 1983 1993 2003 Thanks to J. Luhmann

12. The long decline of Solar Cycle 23 has been marked by very few, well separated Active Regions (GONG website movie, MSFC sunspot illustrations)

13. Comparison of • Large-Scale • Corona in • Cycles 21 & 23 • Panels spaced • By 12 rotations. • CYCLE 23: • Longer • Fewer Contours • Gradual Flattening • Structures Persist • More Dipole in • Declining Phase Cycle 21 Cycle 23

14. Comparison of • Large-Scale • Corona in • Cycles 22 & 23 • Panels spaced • By 12 rotations. • Cycle 23: • Fewer Contours • Slower Flattening • Structures Persist • Thanks to Weak Poles • Both Dipolar During • Reversal Cycle 22 Cycle 23

15. Back to the Photospheric Field

16. Zonal Average of Total Flux and Net Flux – 3 Cycles 1976-2009 from WSO ~2001 WSO Sensitivity

17. Antisymmetric Zonal Old Polarity Surge 2003/4 Symmetric Zonal

18. Toroidal (East-West) Field – 3 Cycles from WSO Cycles overlap several years and are extended

19. Toroidal (East-West) Field – One Cycle from MDI New Cycle 24 1996 2008 Slight offset to positive begins 2002/2003 Leyan Lo, PH Scherrer & JT Hoeksema

20. Comparison of SSN for last 5 Cycles From wattsupwiththat website

21. Perspective Comes from Taking the Long View From Wikipedia website

22. Summary - 1 • Cycle 23 was longer and weaker (relative to 21 and 22): • MF, pole, meridional flow, corona, solar wind, dipole • Polar Reversal on time, but no subsequent growth – no organized poleward migration • Corona/Heliosphere not constrained by dominant Polar Coronal Holes

23. Summary - 2 • Corona/Heliosphere not constrained by dominant Polar Coronal Holes in declining phase of Cycle 23 • HCS continues to reach high latitude • Mid latitude structure in solar wind and low latitude coronal holes • Very few spots in last few years.

24. Summary - 3 • Zonal Flux Reduced • Poleward flows small • Antisymmetric flows at low latitude only • 2002 not like 1991, 1981 • Old polarity anti-symmetric flow in 2003 • Interesting to learn what was ‘absent’ in 2003-2004 • Toroidal flux pattern about the same • New flux emerges just after previous max at high latitude and expands equatorward