On the Extrapolation of the Sun to the Heliosphere

R. A. HowardACE / SOHO / STEREO / WIND Workshop

8-10 June 2010

Outline

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

context

Potential Field Source Surface

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)

• 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

start date Apr 22, 2010

From http://gong.nso.edu

• 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.

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

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

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)

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.

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.

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.

Long Term Coronal Brightness

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.

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

Total Intensity at 4 Rsun

Total intensity is ~2% higher at this minimum than last.

+10% -7%

Long Term CME Mass

Yearly Average CME Mass

• Left plot is the mass in grams• Right plot is the mass in g/area

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

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 & Howard1993)

HI-Imagers Observations of Solar Wind Structures

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.

Example of “J-map” for SECCHI/HI

CIR tracks converge in A and diverge in B

Tracks converge in A Tracks diverge in B

Rouillard et al., GRL, 2008; Rouillard et al., JGR, 2008

Sheeley et al., ApJ, 2008, Sheeley et al., ApJL., 2008

• 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

Tracking CIRs

Wood et al (ApJ, 2010)

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.

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.