1. Weaker Solar Wind Over the Protracted Solar Minimum Dave McComas Southwest Research Institute San Antonio, TX With input from and thanks to Heather Elliott, Nathan Schwadron, and Ruedi von Steiger

2. Ulysses’ Three Polar Orbits

3. Comparison of SWOOPS SW plasma data from Ulysses’ 1 st and 3 rd (Solar Minimum) Orbits McComas et al., GRL, 2008

4. SWOOPS first and third orbits (> 40°) Parameter - v p (km s -1 )761739 -3% v α (km s -1 )772746 -3% n p R 2 (cm -3 )2.652.19 -17% n α R 2 (cm -3 )0.120.10 -17% T p R x10 5 (K)2.662.30 -14% Mass Flux (kg m -2 s -1 ) ρ i v i R 2 x10 -15 3.963.17 -20% Dynamic Pressure (nPa) ρ i v i 2 R 2 3.012.34 -22% Proton Thermal Pressure (pPa) n p kT p R 3 9.897.43 -25% Alpha to proton ratio, n α /n p 0.0440.044 -----  Long term reduction in pressure inflating Heliosphere McComas et al., GRL, 2008

5. Heating in Subsonic Region Nearly all of the energy of the solar wind is carried off in the form of bulk flow energy  excellent measure of the average energy being introduced in the corona, which ultimately accelerates the solar wind Leer and Holzer [1980] developed a simple model to examine the effects of solar wind energization by heating and momentum addition –addition of energy above the sonic point primarily increases the wind speed –addition of energy below the sonic point increases the mass and momentum flux roughly comparably, leading to little change in wind speed  higher density McComas et al., GRL, 2008

6. Ulysses (black) compared to ACE (red) Shows that reduction in SW power is truly global phenomenon

7. Electron Properties Electron density and temperature deduced using quasi- thermal noise spectroscopy Compared 3 rd orbit PCH data with 1 st orbit ~19% less dense (confirms SWOOPS ~17% lower protons and alphas) ~13% lower electron temperature (similar to SWOOPS ~14% lower proton temperature) Issautier et al., GRL, 2008

8. IMF 1 st vs 3 rd Orbits (Ulysses) Smith and Balogh, GRL, 2008

9. IMF Observations Earth-based magnetograph observations indicated that the Sun’s polar cap field strength, Bp, decreased by a factor of about two between 1 st and 3 rd polar passes Ulysses measurements show that the average value of r**2 Br decreased from –3.6 nT (AU)**2 in 1993.5 to 1995.0 –2.3 nT (AU)**2 in 2006.1 to 2007.4 –Decreased by factor of 0.64, but not precisely at minimum Averages of in-ecliptic Br at the two solar minima are 2.82 and 2.45 nT (13% reduction) Decreases contrary to observation based on previous solar cycles that Br returns to the same value of ~3 nT at solar minima Smith and Balogh, GRL, 2008

10. Magnetic Field Fluctuations Decreased Smith and Balogh, GRL, 2008

11. THE SOLAR WIND POWER FROM MAGNETIC FLUX Reduction in high latitude fast SW power in Ulysses 3 rd orbit compared to 1 st correlates with reduction in Sun’s total open magnetic flux These observations support models of the SW energy and particle sources (Schwadron & McComas, 2003; Schwadron et al., 2006) –Constant electromagnetic energy input per particle (assumed) –Magnetic flux emergence naturally leads to an energy flux proportional to the strength of large-scale magnetic field Schwadron and McComas, ApJ, 2008

12. Solar wind mass flux vs. magnetic flux density Schwadron and McComas, ApJ, 2008 Sun delivers ∼ 600 kW/Wb to power the solar wind This power to magnetic flux relation extremely stable over Ulysses’ three polar orbits

13. SW Power in Astrophysical context Schwadron and McComas, ApJ, 2008 SW observation in context of X-ray results of Pevtsov et al., 2003 Black line is 600 kW / Wb as shown in previous plot Red line shows the power X-ray luminosity of ~1% of total SW power (Schwadron et al. 2006)

14. So what has happened in the solar wind since 2007 (2008 publications) ???

15. Not 2007 – 2010!

16. Solar Minimum has Extended

18. Recent Data (and end of Ulysses)

19. Ram Pressure of typically ~3 nPa Down by a Factor of ~2

20. OMNI - CMEs Removed

21. Summary Ulysses’ 3 rd orbit showed fast SW was slightly slower, significantly less dense, cooler, had less m, p, and E flux and weaker IMF than previous solar minimum (first) orbit Combined ACE/Ulysses show that this is a significant, long-term change in SW output from the entire Sun Similar SW speeds with lower power indicates SW energy fed in below the sonic point Charge states indicate coronal temperatures lower Significant, long-term trend to lower dynamic pressure  Heliosphere has been shrinking (Voyager & IBEX) Same law that governs energy released in the corona and from other stars also applies to the total energy in the solar wind Decreasing SW power has continued through 2009 approaching ~1.5 compared to ~3 pPa 20 years ago