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Distribution Functions of Sizes and Fluxes Determined from Supra-Arcade Downflows  

David E McKenzie   Submitted: 2011-06-22 14:58

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: D.E. McKenzie and S.L. Savage
Projects: Yohkoh-SXT

Publication Status: ApJL (published)
Last Modified: 2011-06-23 09:22
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Flare Physics in the Hinode Era (Keynote)  

David E McKenzie   Submitted: 2009-05-19 16:13

Hinode's manifest of instrumentation was conceived to investigate the magnetic connections through the photosphere, lower atmosphere, and corona. The complementarity of the instruments is indeed useful, as demonstrated in numerous flares and eruptions in just the first two years of operation. I will review some of the findings from Hinode's observations of flares to date. It is true, of course, that Hinode's capabilities have evolved since launch. These changes cause the planning of observations to be more complex, and the analysis to be less straightforward; but they do not diminish Hinode's ability to produce important observations of solar flares. On the contrary, Hinode is poised to make truly surprising discoveries. I will explain why this is so, and why we should look forward to the challenge of the coming activity cycle.

Authors: David E. McKenzie
Projects: Hinode/EIS,Hinode/SOT,Hinode/XRT

Publication Status: Accepted for publication in Hinode-2 proceedings.
Last Modified: 2009-05-20 09:24
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Hinode XRT observations of a long-lasting coronal sigmoid  

David E McKenzie   Submitted: 2009-05-19 16:04

Aims: Coronal sigmoids are important sources of eruptions into interplanetary space, and a handful of models have been proposed to explain their characteristic S shape. However, the coronal X-ray images available to date have generally not had sufficient resolution to distinguish between these models. The goal of the present investigation is to determine whether the new observations from Hinode can help us to make such a distinction. Methods: We present the first observations of a persistent coronal sigmoid obtained with the Hinode X-Ray Telescope (XRT). The excellent angular resolution of XRT (1 arcsec per pixel) and the sigmoid's location near disk center combined to provide an unprecedented view of the formation and eruption of this phenomenon. We compared the observed morphology with expectations inferred from two popular models of sigmoid formation, the bald-patch separatrix surface model and the kinking flux rope model. Results: The images during the pre-eruptive phase show that the overall S shape of the sigmoid comprises two separate J-shaped bundles of many loops. The straight sections of the two J patterns lie anti-parallel to one another in the middle of the S, on opposite sides of the magnetic polarity inversion line. The images during the eruptive phase reveal that, before any soft X-ray flaring begins, a diffuse linear structure almost as long as the sigmoid lifts off from the middle of the S. It shows slight clockwise rotation. The X-ray flare begins with the appearance of a sheared arcade of short loops, in the area centered between the two J-shaped patterns of the sigmoid. Conclusions: Taken together, the observational findings provide strong support for the bald-patch separatrix surface model for this sigmoid.

Authors: D. E. McKenzie and R. C. Canfield
Projects: Hinode/XRT

Publication Status: Published in Astronomy & Astrophysics (2008), v.481, L65-L68
Last Modified: 2009-05-20 09:24
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Quantitative Examination of Supra-Arcade Downflows in Eruptive Solar Flares  

David E McKenzie   Submitted: 2009-05-19 15:43

Downward motions above post-coronal mass ejection flare arcades are an unanticipated discovery of the Yohkoh mission, and have subsequently been detected with TRACE, SOHO/LASCO, SOHO/SUMER, and Hinode/XRT. These supra-arcade downflows are interpreted as outflows from magnetic reconnection, consistent with a three-dimensional generalization of the standard reconnection model of solar flares. We present results from our observational analyses of downflows, which include a semiautomated scheme for detection and measurement of speeds, sizes, and-for the first time-estimates of the magnetic flux associated with each shrinking flux tube. Though model dependent, these findings provide an empirical estimate of the magnetic flux participating in individual episodes of patchy magnetic reconnection, and the energy associated with the shrinkage of magnetic flux tubes.

Authors: D. E. McKenzie and Sabrina L. Savage
Projects: TRACE,Yohkoh-SXT

Publication Status: Accepted for publication in ApJ
Last Modified: 2009-05-20 09:24
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Supra-arcade Downflows in Long-Duration Solar Flare Events  

David E McKenzie   Submitted: 2000-02-15 08:05

This report seeks to introduce the reader to a set of observations made during the decay phase of long duration event (LDE) flares on the Sun. In a number of events, the soft X-ray images from Yohkoh SXT indicate a downward directed flow field in the region immediately above the flare arcade. The prototypical event is the M5 flare of 20 January 1999, presented by McKenzie & Hudson (1999); since the time that paper was completed, eleven more events, all related to coronal mass ejections, have been found in the interval 01 January 1998 to 08 May 1999. As in the 20 January event, the speeds of downflow are 45 - 500 km s-1, lower than both the freefall speed and the typically assumed Alfvén speed. A comparison is drawn between the SXT observations and the EUV and Hα data, where such are available. Important additions to our knowledge since the first paper are: (i) the motion is evidenced by both dark and bright (i.e., X-ray emitting) features, some of which may have a looplike morphology; (ii) no cool counterparts have been detected in Hα or EUV observations. The data are compared to the expected appearance according to two likely (and opposing) interpretations: an "above-the-arcade coronal rain" interpretation and a "shrinking magnetic flux tube" interpretation. In the current standard explanation of the formation of post-CME arcades, motion of the latter type may be related to outflow from a reconnection site. Movies depicting some of the flare events are on the accompanying CD-ROM. NOTE: Until the CD-ROM Solar Physics issue comes out, the movies will be online at: http: //solar.physics.mo- //solar.physics.montana.edu/mckenzie/Pubs/Movies/

Authors: McKenzie, D. E.
Projects:

Publication Status: Solar Physics (in press)
Last Modified: 2000-02-15 08:05
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X-Ray Observations of Motions and Structure above a Solar Flare Arcade  

David E McKenzie   Submitted: 2000-02-15 08:04

  In this Letter, we describe a solar flare that was observed by Yohkoh in 1999 January 20. This long-duration event is notable because the Yohkoh images show not only the formation of the arcade associated with the coronal mass ejection but also a considerable amount of motion above the arcade in the region normally identified with a large-scale current sheet or the outflow from magnetic reconnection in the current sheet. A number of arcade events of this morphologi- morphological type (i.e., a fan of spikelike ``rays'' above the posteruption loops) have been seen by Yohkoh, but in this case we have a much clearer view of mass motions in the region above the arcade. The motions indicate field-line retraction without the formation of long-lasting cusps during the rise phase of the flare, and a downward flow above the arcade during the decay phase. The late-phase downward motion is in the form of X-ray dark voids moving at 100-200 km s-1, i.e., at velocities much smaller than the free-fall speed or the assumed Alfvén speed. We interpret the voids as cross sections of evacuated flux tubes resulting from intermittent reconnection following the associated coronal mass ejection. We believe these data represent the first direct evidence of high-speed flows in the region immediately above the flare loops.

Authors: McKenzie, D. E.; Hudson, H. S.
Projects:

Publication Status:
Last Modified: 2000-02-15 08:04
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Abstracts by Author
Distribution Functions of Sizes and Fluxes Determined from Supra-Arcade Downflows
Flare Physics in the Hinode Era (Keynote)
Hinode XRT observations of a long-lasting coronal sigmoid
Quantitative Examination of Supra-Arcade Downflows in Eruptive Solar Flares
Supra-arcade Downflows in Long-Duration Solar Flare Events
X-Ray Observations of Motions and Structure above a Solar Flare Arcade

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