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Development of a Current Sheet in the Wake of a Fast CME  

David Webb   Submitted: 2014-01-06 09:18

A bright ray that developed in the wake of a fast coronal massejection (CME)on 2005 September 7 presents a unique opportunity to study the earlydevelopmentand physical characteristics of a reconnecting current sheet.Polarizationbrightness images from the Mk4 K-Coronameter at the Mauna Loa SolarObservatory(MLSO) are used to determine the structure of the ray along its axis lowin the corona as it progressed outward. Coverage of the earlydevelopment of theray out to ~1.3 R⊙ for a period of ~27 hours after the start ofthe event enablesfor the first time in white light a measurement of a CME current sheetfrom thetop of the arcade to the base of the flux rope. Measured widths of theray arecombined to obtain the kinematics of the upper and lower ''Y'' pointsdescribedin reconnection flux-rope models such as Lin and Forbes (2000). Thetime dependenceof these points are used to derive values for the speed and accelerationof the growth of the current sheet. We note the appearance of a largestructurewhich increases in size as it expands outward in the early developmentof the ray,and an apparent oscillation with period of ~0.5 hour in the positionangle of theray.

Authors: A.G. Ling, D. F. Webb, J. T. Burkepile, E. W. Cliver
Projects: MLSO Mk4 K-Coronameter

Publication Status: ApJ Accepted
Last Modified: 2014-01-06 09:18
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Solar Eruptive Phenomena  

David Webb   Submitted: 2011-08-24 12:04

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: David F. Webb and Timothy A. Howard
Projects: None

Publication Status: Invited review to be published in Living Reviews in Solar Physics.
Last Modified: 2011-08-24 12:08
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Observational Evidence of New Current Sheets Trailing CMEs  

David Webb   Submitted: 2003-09-04 15:46

Field line reconnection in the wake of coronal mass ejections (CMEs) is a fundamental aspect of some magnetically driven eruptive flare/CME models, e.g., the standard reconnection model (cf., {Svestka and Cliver,} 1982). This model features a growing hot loop arcade beneath a rising X-type neutral point that is connected to the retreating CME. In models invoking reconnection, the rising CME and neutral point are connected by a stretched current sheet. Two recent models, {Lin and Forbes} (2000) and {Linker et al.} (2003), predict that an extended, long-lived current sheet must be formed for any physically plausible reconnection rate. Lin and Forbes derive estimates for heights or lengths of current sheets and the energy input as functions of time. In a previous observational study of SMM CMEs observed from 1984-1989 having candidate magnetic disconnection features, primarily transient concave-outward bright regions following the CME leading edge, we found that about half were followed by coaxial, bright rays suggestive of newly formed current sheets. The rays appeared relatively suddenly several hours after the main CME had left the field of view. In this paper we present the results of analysis of these structures, including their heights and lengths, widths, alignments and motions, all as functions of time, and show that they are consistent with the existence of current sheets lasting for several hours and extending more than 5 solar radii into the outer corona.

Authors: Webb, D.F., J. Burkepile, T.G. Forbes and P. Riley

Publication Status: JGR-A (in press)
Last Modified: 2003-09-04 15:48
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The Origin and Development of the May 1997 Magnetic Cloud  

David Webb   Submitted: 2000-08-28 16:00

A complete halo coronal mass ejection (CME) was observed by the SOHO LASCO coronagraphs on May 12, 1997. It was associated with activity near Sun center, implying that it was aimed Earthward. Three days later on May 15 an interplanet- interplanetary shock and magnetic cloud/flux rope transient was detected at the WIND spacecraft 190 Re upstream of Earth. The long enduring southward magnetic fields associated with these structures triggered a geomagnetic storm. The CME was associated with a small coronal arcade that formed over a filament eruption with expanding double ribbons in Hα emission. The flare was accompanied by a circular EUV wave, and the arcade was flanked by adjacent dimming regions. We surmize that these latter regions marked the feet of a flux rope that expanded Earthward into the solar wind and was observed as the magnetic cloud at Wind. To test this hypothesis we determined key parameters of the solar structures on May 12 and compared them with the modeled flux rope parameters at Wind on May 15. The measurements are consistent with the flux rope originating in a large coronal structure linked to the erupting filament, with the opposite-polarity feet of the rope terminating in the depleted regions. However, bidirectional electron streaming was NOT observed within the cloud itself, suggesting that there is not always a good correspondence between such flows and ejecta.

Authors: D.F. Webb, R.P. Lepping, L. Burlaga, C. DeForest, D. Larson, S. Martin, S.P. Plunkett, and D.M. Rust.

Publication Status: JGR, Vol. 105 , No. A12 , 27,261
Last Modified: 2000-12-08 12:57
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Abstracts by Author
Development of a Current Sheet in the Wake of a Fast CME
Solar Eruptive Phenomena
Observational Evidence of New Current Sheets Trailing CMEs
The Origin and Development of the May 1997 Magnetic Cloud

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