1. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions The role of coronal mass ejections in the solar cycle evolution of the heliospheric magnetic field M.J. Owens, N.U. Crooker, N.A. Schwadron, H.E. Spence and W.J. Hughes Center for space physics Boston University

2. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Overview 1.Background 2.Heliospheric flux variation 3.Heliospheric polarity reversal 4.Suprathermal electrons 5.Conclusions

3. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Solar cycle: photosphere 1995 Mt. Wilson magnetographs 2001

4. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Solar cycle: Heliosphere Jones et al., 2003e.g. Richardson et al., 2002

5. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Solar cycle: corona Yang Liu, SHINE 2006 Riley et al., 2006

6. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions How does the coronal field evolve? Wang & Sheeley: Emerging loops bring about field reversal by destruction of existing open flux –Series of PFSS solutions Fisk & Schwadron: Open flux is conserved, but reconfigured by reconnection B.C. Low: Magnetic helicity conservation means potential state cannot be reached by reconnection alone –CMEs required to shed the helicity –CMEs bodily remove flux to allow field reversal

7. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Influence of CMEs on corona Luhmann et al., 1998

8. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Heliospheric flux variation How can you add flux to the heliosphere?

9. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Suprathermal electrons a b c d

10. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Interplanetary CMEs Crooker et al., 2004 Marubashi., 1997

11. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions ICMEs contain closed fields Riley et al., 2004 1 AU: Shodhan et al., 2002 5 AU: Crooker et al., 2002

12. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Flux added by ICMEs must be removed No “flux catastrophe” –McComas et al, 1992 –Equivalent fields must open Two possibilities: –Disconnect open fields –Open CME closed loops via interchange reconnection (Crooker et al., 2002) a b

13. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Flux added by a single CME Owens and Crooker, 2007

14. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Timescale for flux opening Disconnection and interchange reconnection add/remove flux at same rate if rate of reconnection is the same Assume exponential decay to flux from a single CME added to heliosphere t – time since launch φ – flux contained in CME D – fraction of flux which opens at launch λ – decay constant Interchange Disconnection 2

15. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Heliospheric flux budget Assume a constant CME rate: Equate open flux at min/max (i.e., assume variation in |B| is entirely due to ICMEs) T 1/2 ~ 40 days

16. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions LASCO-driven simulation LASCO CMEs have been catalogued. Use LASCO CME times to drive simulation. At each time-step, insert new CMEs and decay flux from existing ICMEs. Observed variability in |B| can be very well matched Owens and Crooker, 2006

17. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Suprathermal electrons Method of reconnection important for heliospheric field evolution Simple picture: –Interchange: no EDs, decay in CSE –Disconnection: EDs, no decay in CSE a b

18. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Observable test Owens et al, 2007 Crooker and Webb, 2006

19. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Crooker et al, 2008

20. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Transport of flux Interchange reconnection transports open flux across CME footpoints

21. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions CME footpoints Polarity of CME footpoints. –Magnetic cloud observations Bothmer and Schwenn, 1998

22. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Rise phase Time Owens et al, 2007

23. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Declining phase Time Owens et al, 2007

24. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Prediction Owens et al, 2007 Crooker and Webb, 2006

25. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Number of CMEs required to reverse polarity: Is there sufficient flux? Timescale for such a reversal d > 5 o

26. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Suprathermal electrons Method of reconnection important for heliospheric field evolution Simple picture: –Interchange: no EDs, decay in CSE –Disconnection: EDs, no decay in CSE

27. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Suprathermal electron scattering Fraction of total electron density 1.00 0.10 0.01 0.3 0.6 1 2 Heliocentric distance (AU) core halo strahl Maksimovic et al., 2005 Hammond et al., 1996

28. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Owens and Crooker, 2007

29. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions How long do closed loops retain the CSE signature? Scattering process is still a topic of research Empirically match observed scattering rate –Can a constant scattering rate reproduce the switch with distance of focusing to scattering?

30. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Numerical simulation Parker Spiral magnetic field Halo electrons move into weaker fields Magnetic moment –μ = V PERP 2 /B

31. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Simulation with pitch-angle scattering

32. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions What’s going on?

33. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Next steps.. Generalise electron model to closed loops Determine length of loop when CSE signature is removed –If it is large, we can we discount reconnection because of too few CSE signatures? –What are the implications for the heliospheric flux budget? –Is the scattering rate in magnetic clouds the same as in the ambient solar wind?

34. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Summary The solar cycle manifests itself in the heliosphere as: –A doubling of the heliospheric flux –A reversal/rotation of the heliospheric current sheet Coronal mass ejections can explain these observations by: –Temporarily adding closed flux to the heliosphere –Transporting open flux across CME footpoints by interchange reconnection close to the Sun The distance at which closed loops lose their identity is important for the heliospheric flux budget

35. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Extra slides

36. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions

37. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions The solar cycle - sunspots

38. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Comparison with Ulysses

39. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Simulation – sine-fit Use simple sine-wave fit to observed CME frequency Owens and Crooker, 2006

40. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Heliospheric flux Solar cycle variation –Approximately doubles over solar cycle –Returns to same value each minimum Richardson et al [2002]: Variation is carried by ambient solar wind, not associated with ICME signatures. Richardson et al., 2002

41. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Suprathermal electrons for a single CME

42. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions LASCO-driven simulation At each time-step, insert new CMEs and decay flux from existing ICMEs. Both interchange and disconnection can explain CSE/EDs observed Different scattering distance

43. 1. Background2. Flux variation3. Polarity reversal4. Electron evolution5. Conclusions Pich-angle scattering