Orientations of Halo CMEs and Magnetic Clouds

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Orientations of Halo CMEs and Magnetic Clouds

• V. Yurchyshyn
• in collaboration with Q. Hu, R.P. Lepping, B.
  Lynch, J. Krall
• BBSO, UC Riverside, GSFC, Univ. Mich., NRL

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Overview
reconnection occurs when CMEs MF and Earths MF
have opposite components
solar eruptions
magnetic cloud, a flux rope
CME
sun
earth
Geo. storm is response of the magnetosphere on
southwardly directed IMF

• Geoeffectiveness of a halo CME depends on
• the field strength in it and
• the orientation of the mag. field

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The MCs Bz - Dst Index Relationship
Yurchyshyn, Hu, Abramenko, 2005, Space Weather,
3, 8, S08C02
Dst index is directly related to the strength of
the Bz (Wu Lepping 2004 Cane et al. 2001)
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CME Speed vs MCs Bz
Yurchyshyn, Hu, Abramenko, 2005, Space Weather,
3, 8, S08C02
Fast CMEs have a greater potential to cause a
significant storm
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Speed of CMEs vs Magnetic Flux
Qiu Yurchyshyn, 2005, ApJL
Yurchyshyn, Hu, Abramenko, 2005, Space Weather,
3, 8, S08C02
High speed CMEs are associated with those flares
where a large amount of the magnetic flux
reconnected. Agrees w/ previous conclusion that
CME speed is related to the Bz
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Summary of the Introduction

• Thus, the intensity of Bz component can be
  predicted based on solar data (magnetograms,
  Halpha, TRACE and/or LASCO images)
• What about the orientation?
• Many (mainly case) studies argue that the
  orientation and helicity of the magnetic field of
  CME source regions (mainly ARs) agree very well
  with those of the corresponding MCs.

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Halo CMEs

• CMEs observed near the earth often exhibit a
  magnetic structure that can be described as
  complex ejecta, magnetic clouds, plasmoids or
  shocks. Well defined MCs are associated with
  30-50 of CMEs
• MC, in turn, have magnetically organized geometry
  that is thought to correspond to a curved flux
  rope (Burlaga 1981 Bothemer Schwenn 1998)

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White Light Structure of CMEs
White light morphology of CMEs seems to bear
information on their magnetic structure they are
organized in the axial direction, which
corresponds to the axis of the underlying
erupting flux rope (Cremades Bothmer, 2004)
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Halo CMEs are

• 2D projection of a 3D structure and they
  often exhibit various sizes and shapes. Many of
  them can be enveloped by an ellipse and fitted
  with a cone model (Zhao, Plunkett Liu 2002, Xie
  Ofman Lawrence 2004 Zhao 2005)

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Halo CMEs and Erupting Flux Rope Modeling
In this study we assume that halo elongation
indicates the orientation of an erupting flux rope
sun
Model halo CME
top view
earth
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Oct 28 and Nov 18 2003 Events
Nov 18 2003
Elongation of a halo CME closely matches the
orientation of the erupting flux rope
Oct 28 2003
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Data Analysis

• Selected 25 halo CME -- MC events
• Determined the orientation of CMEs
• Determined the clock angle of MCs
• Grad-Shafranov MC reconstruction by Q. Hu
• MC fitting by Lepping et al. (2006)
• MC fitting by Lynch et al. (2005)
• MC fitting with the EFR model (J. Krall V.
  Yurchyshyn)

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Orientation of 25 halo CMEs
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Results
Ovals CMEs, lines MCs. Short lines are used
when the difference between CME and MC
orientations, ??, exceeds 45 deg. Black dotted
line mean MC orientation angle Green boxes 15
events (60) ?? lt 45 deg Red boxes 8 events
(32) ?? gt 45 deg Blue boxes 2 events (8) ?? ?
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What Does This Result Mean?

• For 60 of events (green) CME elongation agrees
  with MC orientations
• What about the red events? Was our initial
  assumption wrong? Or is there something that
  affects a coronal ejecta? Is there any systematic
  difference between the CMEs and MCs?
• Can MCs be deflected and their orientation
  changed during the propagation toward the Earth?

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CMEs Heliospheric Current Sheet

• CMEs disrupt heliospheric magnetic fields (Zhao
  Hoeksema 1996)
• Fast moving CMEs interact w/ upstream plasma,
  shock formation (Gosling et al., 1994 Howard
  Tappin 2006, Liu Hayashi 2006)
• CMEs may displace and push the heliospheric
  magnetic fields (Smith 2001)
• Most CMEs may be associated with HCS, which is
  considered to be a conduit for CMEs (Crooker et
  al., 1993)
• Does the heliosphere affects CMEs?

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Comparison between CMEs, HCS and MCs
CME
Wilcox Solar Observatory Coronal Field Map at 2.5R
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Results of the Comparison

• 13 events CME,MClt45 deg and MC agrees w/HCS
• 7 events CME,MCgt45 deg, while MC agrees w/HCS
• 2 events CME,MClt45 deg, however MC ? HCS
  (Vgt2000km/s)
• 1 event CME,MCgt45 deg, MC is ? to HCS
• 2 events uncertain

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Orientations of CMEs, HCS and MCs are similar
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Do CMEs rotate to align w/HCS?
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Are Fast CMEs not affected by HCS?
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Conclusions

• For about 60 of events the halo elongation and
  the MC orientation correspond to the local tilt
  of the HCS
• For majority of solar ejecta (80), the
  underlying erupting flux rope at 1AU (i.e. MC)
  aligns itself with the HCS
• It seem that very fast (Vgt2000km/s, 2 events)
  CMEs maintain their orientation constant
• There is an indication that the degree of CME
  rotation , if indeed occurs, might depend on the
  speed of a CME faster CMEs are less affected by
  the HCS (shorter interaction time? stronger
  CMEs?)
• The data seem to support our initial assumption
  although the results should be tested on a larger
  data set

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Conclusions
The data seem to support original assumption that
the CME elongation represent the axis of an
erupting flux rope