On the Extrapolation of the Sun to the Heliosphere

1. On the Extrapolation of the Sun to the Heliosphere R. A. Howard ACE / SOHO / STEREO / WIND Workshop 8-10 June 2010

2. Outline • PFSS Modeling • Long-term brightness of corona • Long-term mass of CMEs • Use of HI-type of imaging to see solar wind context

3. Potential Field Source Surface

4. PFSS • Input data – 27.3 days of photospheric line-of-sight magnetic field • Solve the equation: where • Assumptions • Potential Field • Field is radial at the “source surface”, generally 2.5Rs, beyond which all field lines are “open” • No changes during the 27 days of observation • It works • Describes well the locations of CHs & current sheet (i.e. neutral line)

5. start date Apr 22, 2010 • Blue lines are the highest closed field lines below the source surface (at 2.5 Rs) and delineate the boundaries of open and closed flux • Green area is (+) magnetic flux • Red area is (-) magnetic flux • Black line is the magnetic neutral line From http://gong.nso.edu

6. Shows changes between CR 2095 and CR 2096 • Foot point locations that underlie closed/open field and thenand open/closed field in the second • Opening foot points are in blue and closing in red fields • Coronal holes are in green. • Note that the changes are generally at the boundaries of coronal holes.

7. Comparison of Computed & Observed Streamer Location (1) • Columns the same except data source • Left: Mt Wilson (MWO) • Right: Wilcox (WSO) • Top row – magnetic field synoptic map (degraded resolution) • 2nd Row – PFSS computed neutral line (opposite Bfield) and pseudo line (same Bfield) at 2.5 Rs SS • 3rd Row – computed streamers • 4th Row – observed (LASCO) streamers (same on both columns) • In general, comparison is good. • But in detail, there are differences Wang et al ApJ2009

8. Comparison of Computed & Observed Streamer Location (2) • Different results for MWO and WSO • Fluctuation in density along the NL axis is not observed • Upticks in streamers • Small CMEs & perhaps evolutionary effects • Can’t distinguish between evolutionary effects and model problems. Wang et al ApJ2009

9. Other Examples of PFSS Modeling • Left column from Feb, 1997 • Right column from Apr, 1998 • Again, general agreement is good, but some details are not captured. • Why the discrepancy? Wang et al (JGR, 2000)

10. Problems with Assumption of Constant 3D Field Topology • Does not account for • Evolutionary changes • Newly emerged bipolar regions • CMEs that disrupt the large scale pattern • Presumably CMEs that don’t disrupt the l.s. pattern don’t affect the modeling • But the field lines that get opened by any CME, don’t stay open forever – they must close down eventually.

11. Problems with Potential Field Assumption • The PF is the lowest energy state – the state that the Sun is trying to reach. • But CMEs are certainly non-potential • The floor of CME activity is about 0.2-1 CME/day. These are “streamer-blowout”s that occur at the same rate throughout the solar cycle and are presumably due to photospheric sheering. They are flux-rope forms and have been the dominant form of late. • STEREO/SECCHI loop analyses show non-potential structures in ARs – they have tried to put in force-free analysis, but it is still not sufficient.

12. Some Major Problems • By definition, all solar wind comes from open field regions • But slow wind has compositional signatures associated with the quiet sun, not CH • Somehow this plasma gets out which is incompatible with both PFSS and MHD • Small scale variations are not considered - the PFSS solution is a global solution. • Is this due to computational limitations? • We have seen 10x variations in density along a streamer over a 60° longitude range.

13. Long Term Coronal Brightness

14. Equatorial Brightness 1996-2008 The yellow line is to guide your eye. The last minimum is about 10% brighter than from 1998 and later. This is due to the dipole nature of the last minimum.

15. Streamer Intensity & Location Note the transition of the position to southern hemisphere in mid 2003, but no change in the intensity until 2004 (~5%).

16. Total Intensity at 4 Rsun +10% -7% Total intensity is ~2% higher at this minimum than last.

17. Long Term CME Mass

18. Yearly Average CME Mass • Left plot is the mass in grams • Right plot is the mass in g/area

19. Total CME Mass Per CR • Steady increase from minimum in 1996 to maximum in 2000. • Constant through maximum • Steady decrease to current minimum, although a cyclic nature of about 6 CR • Average mass per CR about the same in the two minima

20. Comparison of LASCO to Solwind CMEs • The LASCO CMEs have a similar distribution to Solwind, but significantly lower mass. • The difference is too large to be a calibration difference. • Is it due to a difference in the cycles? Solwind distribution (From Jackson & Howard 1993)

21. HI-Imagers Observations of Solar Wind Structures

22. J-Maps • Developed by a student of Neil Sheeley’s over several summers (Jeffrey Walters). Also developed by Jackie Davis at RAL • They are plots of time vs elongation (apparent height) • Similar to the synoptic maps but here time increases to the right. • First form a running difference movie from the direct images • For each image (ie time) extract a narrow rectangular window at a particular Position Angle from an image and placing it in a large array and then do it again at the same PA at the next time. • Very useful for tracking CMEs, CIRs and Blobs through the inner heliosphere.

23. Example of “J-map” for SECCHI/HI

24. CIR tracks converge in A and diverge in B Tracks converge in A Tracks diverge in B Sheeley et al., ApJ, 2008, Sheeley et al., ApJL., 2008 Rouillard et al., GRL, 2008; Rouillard et al., JGR, 2008

25. Streamer blobs can be tracked throughout the HI1/2 fields of view. • Sheeley & Rouillard (ApJ, 2010) show that they become swept up and compressed by the fast wind from low-latitude coronal holes. • Account for many of the non-CME features in the elongation-time maps

26. Tracking CIRs Wood et al (ApJ, 2010)

27. Modeling CIR Evolution • Solar wind density, speed, and B-field from ACE, SOHO, STEREO-A/B • The dotted lines show the timing predicted by the model of Wood et al, 2010.

28. Summary • PFSS does a good job in reproducing the CH and neutral line boundaries • There are known departures from the assumptions of a 27-day unchanging 3D potential magnetic field structure • The long-term coronal brightness and CME mass show variations, but not consistent with the dynamic pressure decrease observed from Ulysses. • Elongation-time (J-) maps are necessary to track features in the imagers from the Sun to 1 AU – straight-lines in height-time maps are wrong.