On the Extrapolation of the Sun to the Heliosphere

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On the Extrapolation of the Sun to the Heliosphere

• R. A. Howard
• ACE / SOHO / STEREO / WIND Workshop
• 8-10 June 2010

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Outline

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

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Potential Field Source Surface
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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)

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start date Apr 22, 2010
From http//gong.nso.edu

• 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

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• 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.

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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
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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
• Cant distinguish between evolutionary effects
  and model problems.

Wang et al ApJ2009
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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)
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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 dont disrupt the l.s.
  pattern dont affect the modeling
• But the field lines that get opened by any CME,
  dont stay open forever they must close down
  eventually.

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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-blowouts 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.

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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.

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Long Term Coronal Brightness
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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.
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Streamer Intensity Location
Note the transition of the position to southern
hemisphere in mid 2003, but no change in the
intensity until 2004 (5).
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Total Intensity at 4 Rsun
10 -7
Total intensity is 2 higher at this minimum
than last.
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Long Term CME Mass
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Yearly Average CME Mass

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

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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

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Comparison of LASCO to Solwind CMEs
Solwind distribution (From Jackson Howard 1993)

• 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?

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HI-Imagers Observations of Solar Wind Structures
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J-Maps

• Developed by a student of Neil Sheeleys 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.

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Example of J-map for SECCHI/HI
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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
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• 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

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Tracking CIRs Wood et al (ApJ, 2010)
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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.

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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.