1. Orientations of Halo CMEs and Magnetic Clouds
V. Yurchyshyn, Q. Hu, R.P. Lepping, B. Lynch, J. Krall
BBSO, UC Riverside, GSFC, Univ. Mich., NRL

2. Introduction
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 (Bothemer & Schwenn 1998)
9/16/2018
2006 SPD Meeting, Durham, NH

3. Three part 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)
9/16/2018
2006 SPD Meeting, Durham, NH

4. Halo CMEs
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)
9/16/2018
2006 SPD Meeting, Durham, NH

5. Halo CMEs and Erupting Flux Rope Modeling
In this study we assume that halo elongation indicates the orientation of an erupting flux rope
sun
Solid – ACE
Dashed – Model
Model
halo CME
top
view
earth
9/16/2018
2006 SPD Meeting, Durham, NH

6. Oct 28 and Nov Events
Nov
Elongation of a halo CME closely matches the orientation of the erupting flux rope
Oct
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2006 SPD Meeting, Durham, NH

7. 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)
9/16/2018
2006 SPD Meeting, Durham, NH

8. Orientation of 25 halo CMEs
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2006 SPD Meeting, Durham, NH

9. 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%)  < 45 deg
Red boxes: 8 events (32%)  > 45 deg
Blue boxes: 2 events (8%)  ?
9/16/2018
2006 SPD Meeting, Durham, NH

10. What Does This Result Mean?
For 60% of events (“green”) the 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?
9/16/2018
2006 SPD Meeting, Durham, NH

11. 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)
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?
9/16/2018
2006 SPD Meeting, Durham, NH

12. Comparison between CMEs, HCS and MCs
Wilcox Solar Observatory Coronal Field Map at 2.5R
9/16/2018
2006 SPD Meeting, Durham, NH

13. Results of the Comparison
13 events CME,MC<45 deg and MC agrees w/HCS
7 events CME,MC>45 deg, while MC agrees w/HCS
2 events CME,MC<45 deg, however MC  HCS (V>2000km/s)
1 event CME,MC>45 deg, MC is  to HCS
2 events – uncertain
9/16/2018
2006 SPD Meeting, Durham, NH

14. Orientations of CMEs, HCS and MCs are similar
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2006 SPD Meeting, Durham, NH

15. Do CMEs rotate to align w/HCS?
9/16/2018
2006 SPD Meeting, Durham, NH

16. Are Fast CMEs not affected by HCS?
9/16/2018
2006 SPD Meeting, Durham, NH

17. 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 (V>2000km/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
9/16/2018
2006 SPD Meeting, Durham, NH

18. Conclusions
The data seem to support original assumption that the CME elongation represent the axis of an erupting flux rope
9/16/2018
2006 SPD Meeting, Durham, NH