Evolution of Magnetic Fields from the Sun’s Surface to the Heliopause of one Solar Cycle Nathan Schwadron, Boston University

Outline Heliosphere’s Hale Cycle Possibilities for Reversing the Heliosphere’s Magnetic Field The Role of CMEs in Field Evolution Observational Support Next Steps Conclusions

The Helisphere’s Hale Cycle N+ S- N- S+ N+ S- N- S+ N- S+

Evolving Magnetic Flux Wang et al., 2000 N+ S- N- S+ N+ S- N+ S- N- S+ N+ S- Roughly factor x2 variation in Open Magnetic Flux

Questions How does the global Field Reverse? What causes variation in Open field strength?

Interchange reconnection (Media Diffusion) Interchange reconnection conserves open magnetic flux Provides a means for reversal of open magnetic flux without changing the net quantity of flux Fisk and Schwadron, 2001

The Role of CMEs CMEs move flux via interchange reconnection CMEs temporarily add closed magnetic flux, increasing |B|, particularly during solar max

Temporary Flux Addition by CMEs Black line shows the observed value of |B| at 1 AU from ACE/Wind Red line shows simulated value of |B| at 1 AU using LASCO observed CME rates CME half-life 50 days Model comparison validates open flux conservation during CME ejections

CMEs and the Hale Cycle CMEs generally have an orientation in agreement in with Hale’s law (Bothmer and Schwenn, Ann. Geophys., 1998) Is the flux opened by Interchange Reconnection sufficient for field reversal? ‣ F open = Open Flux ~10 15 Wb ‣ F CME =CME flux ~10 12 Wb ‣ freq = CME frequency ~ 3/day ‣ d = CME footpoint separation ‣ Number of Needed CMEs, N =(F open /F CME )x(180 o /d) ‣ Time required for field reversal, T = N/freq ≈ 11 years ‣ Solve for footpoint separation d > 5 o

Owens et al., 2006

Confirmation from Suprathermal Electron Observations Does Interchange Reconnection open fields primarily in one or both legs of the CME Answer: One 85% 15% Crooker et al., 2006

Disconnection? Disconnection across the helmet streamer is another process that leads to the reduction of open flux This may be balanced by the addition of flux by CMEs It is difficult to differentiate between disconnection and the effects of large-scale interchange reconnection (flux addition, then I.C.)

Long-Term Evolution Evidence of Open Flux Conservation over Large Timescales (Svalgaard and Cliver, 2007)

Outer Heliosphere Implications New Outer Heliosphere Current Layer

Next Steps Is the Open Magnetic Flux of the Heliosphere Conserved? ‣ Recent Ulysses results may suggest disagreement with Source surface models after the field reversal? ‣ SHINE session: Svalgaard, Murphy, Arge invited speakers Essential at this stage that energetic particle and magnetic field models take into account flux conservation ‣ The Earth-Moon-Mars Radiation Environment Model is designed to couple EP models w/evolving MHD results of the global solar wind ‣ Approach is to develop a mesh in which node lines follow magnetic field lines ‣ Starightforward to use the code framework to understand implications of footpoint motions for the magnetic field over the solar cycle.

Conclusions Coronal Mass Ejections may control the heliospheric Hale Cycle ‣ Changes in |B| through temporary buildup of open flux ‣ Movement of open flux through Interchange Reconnection ‣ Reversal of the Heliospheric Magnetic Field Next Steps ‣ Is the Open Magnetic Flux of the Heliosphere Conserved?  On what timescales and why - fundamental to solar dynamo ‣ Investigate detailed implications for energetic particles (EMMREM) and outer heliosphere configuration  Utilize EPs to probe global structure (requires coupling between EP models and MHD/field models)

Temporary Flux Addition due to CMES Observed CME freq Modeled Owens and Crooker, JGR, 2006 CME flux half-life ~40-55 days

Solar Butterfly Diagram Hathaway, 2003 N- S+ N+ S-S+ N-N+ S-