Title: Orientations of Halo CMEs and Magnetic Clouds
1Orientations of Halo CMEs and Magnetic Clouds
- V. Yurchyshyn, Q. Hu, R.P. Lepping, B. Lynch, J.
Krall - BBSO, UC Riverside, GSFC, Univ. Mich., NRL
2Introduction
- 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)
3Three 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)
4Halo 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)
5Halo 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
6Oct 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
7Data 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)
8Orientation of 25 halo CMEs
9Results
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) ?? (32) ?? 45 deg Blue boxes 2 events (8) ?? ?
10What 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?
11CMEs 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?
12Comparison between CMEs, HCS and MCs
CME
Wilcox Solar Observatory Coronal Field Map at 2.5R
13Results of the Comparison
- 13 events CME,MC
-
- 7 events CME,MC45 deg, while MC agrees w/HCS
- 2 events CME,MC (V2000km/s)
- 1 event CME,MC45 deg, MC is ? to HCS
- 2 events uncertain
14Orientations of CMEs, HCS and MCs are similar
15Do CMEs rotate to align w/HCS?
16Are Fast CMEs not affected by HCS?
17Conclusions
- 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 (V2000km/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
18Conclusions
The data seem to support original assumption that
the CME elongation represent the axis of an
erupting flux rope