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How Many CMEs Have Flux Ropes? Deciphering the Signatures of Shocks, Flux Ropes, and Prominences in Coronagraph Observations of CMEs  

Angelos Vourlidas   Submitted: 2012-07-05 15:46

We intend to provide a comprehensive answer to the question on whether all Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we present a synthesis of the LASCO CME observations over the last sixteen years, assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic observations from extsl{STEREO} and extsl{SDO}, and statistics from a revised LASCO CME database. We argue that the bright loop often seen as the CME leading edge is the result of pileup at the boundary of the erupting flux rope irrespective of whether a cavity or, more generally, a 3-part CME can be identified. Based on our previous work on white light shock detection and supported by the MHD simulations, we identify a new type of morphology, the `two-front' morphology. It consists of a faint front followed by diffuse emission and the bright loop-like CME leading edge. We show that the faint front is caused by density compression at a wave (or possibly shock) front driven by the CME. We also present high-detailed multi-wavelength EUV observations that clarify the relative positioning of the prominence at the bottom of a coronal cavity with clear flux rope structure. Finally, we visually check the full LASCO CME database for flux rope structures. In the process, we classify the events into two clear flux rope classes (`3-part', `Loop'), jets and outflows (no clear structure). We find that at least 40% of the observed CMEs have clear flux rope structures and that sim29% of the database entries are either misidentifications or inadequately measured and should be discarded from statistical analyses. We propose a new definition for flux rope CMEs (FR-CMEs) as a coherent magnetic, twist-carrying coronal structure with angular width of at least 40circ and able to reach beyond 10 Rodot which erupts on a time scale of a few minutes to several hours We conclude that flux ropes are a common occurrence in CMEs and pose a challenge for future studies to identify CMEs that are clearly extsl{not/} FR-CMEs.

Authors: A. Vourlidas, B.J. Lynch, R.A. Howard, Y. Li
Projects: SoHO-LASCO,STEREO

Publication Status: to be published in Solar Physics
Last Modified: 2012-07-07 14:50
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Uncovering the Birth of a Coronal Mass Ejection from Two-Viewpoint SECCHI Observations  

Angelos Vourlidas   Submitted: 2011-12-30 10:49

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: A. Vourlidas, P. Syntelis, K. Tsiganos
Projects: STEREO

Publication Status: Solar Physics (in press)
Last Modified: 2012-01-02 15:28
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Identification of a peculiar radio source in the aftermath of large coronal mass ejection events  

Angelos Vourlidas   Submitted: 2007-01-24 13:29

We report the discovery of a new radio feature associated with coronal mass ejection (CME) events. The feature is a low frequency (<1~MHz), relatively wide (sim 300~kHz) continuum that appears just after the main phase of the eruptive event, lasts for several hours, and exhibits a slow negative frequency drift. So far, we have identified this radio signature in a handful of CME events and suspect it might be a common occurrence. The radio continuum starts almost simultaneously with the commonly observed decimetric type-IV stationary continuum (also called flare-continuum) but the two seem unrelated. The emission mechanism, whether plasma emission or gyroresonance, is unclear at the moment. Based on our preliminary analysis, we interpret this radio continuum as the lateral interaction of the CME with magnetic structures. Another possibility is that this continuum traces the reconfiguration of large-scale loop systems, such as streamers. In other words, it could be the large-scale counterpart of the post-CME arcades seen over active region neutral lines after big CME events. This letter aims to bring attention to this feature and attract more research into its nature.

Authors: A. Vourlidas, M. Pick, S. Hoang, P. Demoulin
Projects: SoHO-LASCO

Publication Status: ApJ Letters (accepted, Feb 20, 2007)
Last Modified: 2007-01-25 09:48
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LASCO Measurements of the Energetics of Coronal Mass Ejections  

Angelos Vourlidas   Submitted: 1999-12-03 13:05

We examine the energetics of Coronal Mass Ejections (CMEs) with data from the LASCO coronagraphs on SOHO. The LASCO observations provide fairly direct measurements of the mass, velocity and dimensions of CMEs. Using these basic measurements, we determine the potential and kinetic energies and their evolution for several CMEs that exhibit a flux-rope morphology. Assuming flux conservation, we use observations of the magnetic flux in a variety of magnetic clouds near the Earth to determine the magnetic flux and magnetic energy in CMEs near the Sun. We find that the potential and kinetic energies increase at the expense of the magnetic energy as the CME moves out, keeping the total energy roughly constant. This demonstrates that flux rope CMEs are magnetically driven. Furthermore, since their total energy is constant, the flux rope parts of the CMEs can be considered to be a closed system above about 2 solar radii.

Authors: Vourlidas, A., Subramanian, P, Dere, K.P., Howard, R.A.
Projects:

Publication Status: ApJ (accepted)
Last Modified: 1999-12-03 13:05
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Abstracts by Author
How Many CMEs Have Flux Ropes? Deciphering the Signatures of Shocks, Flux Ropes, and Prominences in Coronagraph Observations of CMEs
Uncovering the Birth of a Coronal Mass Ejection from Two-Viewpoint SECCHI Observations
Identification of a peculiar radio source in the aftermath of large coronal mass ejection events
LASCO Measurements of the Energetics of Coronal Mass Ejections

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