Tracking CMEs from Sun to Earth

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Tracking CMEs from Sun to Earth

• M. Temmer1, C. Möstl2, A. Veronig1,
  O. Flor1, T. Rollett1,2
• 1 Kanzelhöhe Observatory/IGAM, Institute of
  Physics, University of Graz, Austria
• 2 Space Research Institute Graz, Austrian Academy
  of Sciences
• November 17, 2010 ESWW7 in Brugge, Belgium

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STEREO-SECCHI
STEREO Gallery
1AU

• Seamless obser-vations from Sun to Earth and
  beyond
• SECCHI instrument suite EUVI, COR1, COR2, HI1,
  HI2

• Simultaneous obser-vations from two different
  vantage points
• STEREO-A(head) STEREO-B(ehind)

Howard et al., 2008
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CMEs in 3D space
Vourlidas Howard, 2006

• Close to the Sun, we may assume all emission
  comes from the plane of the sky (POS)
• At large elongation angles the Thomson surface
  becomes more and more significant
• Differences in brightness and morphology
  depending on the angle between observer and CME

See e.g., Cremades Bothmer, 2004
Vourlidas Howard, 2006 Manchester et al.,
2008 Harrison et al., 2010
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From Sun to Earth
Rouillard et al., 2008
Elongation angle
ß
Sun
SC A
Time
Ho1AU
Sheeley et al., 1999
For a single point having a constant speed, the
elongation appears different for various
longitudinal directions of motion
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From Sun to Earth
Rollett, Möstl, Temmer et al., 2010
HI1
HI2

• Combining white light and in situ powerful
  diagnostics
• Valuable constraints on CME direction and
  geometry can be made

Möstl, Farrugia, Temmer et al., 2009 Möstl,
Temmer, Rollett et al., 2010
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Methods

• To derive the directivity of a CME we use
• close to the Sun
• Triangulation
• in IP space
• Sheeley fitting from single s/c measurements

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Triangulation method
Temmer, Preiss Veronig, 2009
Schematic LASCO and ST-A view observing the
leading edge of a CME.
lat(itude)d lon(gitude)f

• Method
• Perform classical leading edge measurements
  (from at least two
  different vantage points)
• Transform LASCO distance-time (dt) measurements
  to STEREO-A and STEREO-B view
  (dependent on lat. and lon.)
• Compare transformed dt with observed dt from ST-A
  and ST-B
• Vary lat. and lon. until best match

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Triangulation method
Example for the March 25, 2008 event
STEREO-B
SOHO-LASCO
STEREO-A
Temmer, Preiss Veronig, 2009
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Triangulation method
Temmer, Preiss Veronig, 2009
Distance-time measurements of CME LE. Solid
lines transformed d-t (based on
LASCO) Dashed lines resulting de-projected
distances (separately for LA and LB) Resulting
distribution of least square sum as a function of
the CME source region longitude f and a fixed
(best) value of the source latitude d.
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Comparison with HI
Selected events which could be tracked over an
elongation angle of more than 30 (HI1HI2)

• December 31, 2007
• January 2, 2008
• March 25, 2008
• April 26, 2008
• May 17, 2008

Separation angle between STA and STB range of
4352
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Base difference images
Method of base difference images used for HI.
Shifting of images needed due to the proper
motion of the spacecraft. About 4 for a
typical minimum event (1/day).
Temmer, et al., 2011, in prep
Apr 26, 2008 (HI1)
Apr 26, 2008 (HI2)
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First results
Dec 31, 2007 (HI1)
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First results
Apr 26, 2008 (HI1)
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First results
Jan 2, 2008 (HI1)
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First results
Mar 25, 2008 (HI1)
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First results
May 17, 2008 (HI1)
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First results
June 1, 2008 event of a velocity of 300-400km/s
studied in Möstl et al. 2009 E45 close to the
Sun and E30 in IP space.
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Conclusions

• Large differences are derived between
  propagation direction close to the Sun and in IP
  space
• Best match for two fast events
  (March 25, 2008 and May 17,
  2008)
• Slow events and fast ones that significantly
  slow down during evolution show large deviation
• Geometrical effects from fixed-phi method
  (assumption of point like feature) Rollett et
  al., 2010 for a comparison between the two
  methods
• Assumption of constant speed (but might be ok
  for solar minimum events see e.g., Morrill et
  al. 2008)
• Compare with Möstl et al., 2009 - almost
  constant direction was obtained for a slow CME
  event