Two-stage SEE Shows Reconnection

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== References ==
== References ==
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Aschwanden, M. J., Wuelser, J. P., Nitta, N. V., & Lemen, J. R. 2009, Sol. Phys., 256, 3
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[http://adsabs.harvard.edu/abs/2009SoPh..256....3A Aschwanden, M. J., Wuelser, J. P., Nitta, N. V., & Lemen, J. R. 2009, Sol. Phys., 256, 3]
Woods, T. N., Eparvier, F. G., Hock, R., Jones, A. R., Woodraska, D., Judge, D., Didkovsky, L., Lean, J., Mariska, J., Warren, H., McMullin, D., Chamberlin, P., Berthiaume, G., Bailey, S., Fuller-Rowell, T., Sojka, J., Tobiska, W. K., & Viereck, R. 2011, Sol. Phys.
Woods, T. N., Eparvier, F. G., Hock, R., Jones, A. R., Woodraska, D., Judge, D., Didkovsky, L., Lean, J., Mariska, J., Warren, H., McMullin, D., Chamberlin, P., Berthiaume, G., Bailey, S., Fuller-Rowell, T., Sojka, J., Tobiska, W. K., & Viereck, R. 2011, Sol. Phys.

Revision as of 19:39, 8 August 2011


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Number: 157
1st Author: Brian Dennis
2nd Author: Yang Su
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Contents

Introduction: A Two-Stage SEE

Using SDO EVE light curves and AIA images, Woods et al. (2011) have shown that in some solar eruptive events (SEEs) a second stage of heating can occur an hour or more after the first. Aschwanden et al. (2009) attributed similar late peaks seen in the EUV light curves from STEREO/EUVI to the cooling of the plasma heated to higher temperatures during the initial energy release. In one well-observed event seen with both STEREO A and B, they estimated a conductive and radiative cooling time of ~40 minutes that they argued was consistent with the observed delay of ~1 hour between the soft X-ray and EUV peaks. Woods et al. (2011), however, claim that this could not possibly be the explanation in at least one case. The hot plasma at ~2 MK that produced the second-stage peak in the EVE light curves was revealed by the AIA images to be from a different location than the plasma in the first stage and hence could not have resulted from the cooling of the initially heated plasma.

Fig. 1. AIA, GOES, and RHESSI light curves of the SEE on 8 March 2011 with temperature and emission measure estimates in the bottom panel.

We report here on an event on 8 March 2011 with similar strong evidence for a second stage of energy release high in the corona. In this event shown in Figure 1, the second-stage energy release was seen as a second peak in the GOES X-ray light curves showing that the plasma was heated to some 15 Mk, almost the same temperature as the plasma heated during the first stage nearly two hour earlier. RHESSI spectral analysis confirms the similarity of the temperatures with ~20 MK for the first peak and 15 MK for the second (shown in Fig. 1, bottom panel). AIA images throughout this event show that the second-stage heating occurred at a much higher altitude in the corona than the first, again confirming that it was not the result of cooling from the first stage.


Magnetic Reconnection

Fig. 2. Still from AIA movie in the 131 Angstrom passband at 20:06:22 UT showing the remarkable similarity to the classical picture of X-point magnetic reconnection.

Another remarkable aspect of this SEE is the visual appearance of magnetic reconnection revealed by the the AIA movies during the second stage of energy release, particularly in the 131 Angstrom passband. First, a rapid ejection of hot plasma was seen starting high in the corona and moving out of the field of view in less than a minute??? This was followed by perhaps the clearest evidence yet for magnetic reconnection in the corona. This is seen best in the movie in the AIA 131 Angstrom passband but Fig. 1 shows an image when the reconnection was well developed. A fine bright line appeared at the start of the second peak followed by what certainly looks like a classic X-point reconnection with initially turbulence below and the later appearance of rapidly falling new bright loops. Emission above the X-point was much fainter but suggested that hot plasma was also driven to higher altitudes at the same time. The whole sequence, lasting ~10 minutes???, had the same basic appearance as the classic model of magnetic connection at an X-point with newly connected field lines pulling rapidly away both above and below. There was minimal evidence for any particle acceleration at this time from the RHESSI light curves at >20 keV. However, any bright hard X-ray footpoints could have been occulted since the flare ribbons were mostly over the limb as revealed by images from STEREO-B, which saw the event at near Sun-center from its perspective at ~90 degrees from the Earth-Sun line.


Conclusion

This well-observed SEE shows clear evidence for two stages of energy release separated by almost two hours. Both the high temperature and higher altitude of the second-stage plasma preclude the possibility that it was merely the same plasma heated during the first stage that had cooled sufficiently to emit in the lower temperature AIA passbands. There was little indication during the first stage that a second stage was imminent although the initial eruption did seem to stall as if it was either too weak to drive the ejection against the Sun's gravity or that there were overlying magnetic fields preventing the plasma from escaping.

This SEE also shows, during the second stage, strong visual evidence for magnetic topology changes, plasma turbulence, and newly formed retracting magnetic loops. The overall appearance during this phase is remarkably similar to the classic picture of X- or Y-point magnetic reconnection. Further analysis is required to establish if observations at other wavelengths support this interpretation.

Authors Notes

Yang Su, Goddard and The Catholic University of America, soon to be at the University of Graz, Austria.

References

Aschwanden, M. J., Wuelser, J. P., Nitta, N. V., & Lemen, J. R. 2009, Sol. Phys., 256, 3

Woods, T. N., Eparvier, F. G., Hock, R., Jones, A. R., Woodraska, D., Judge, D., Didkovsky, L., Lean, J., Mariska, J., Warren, H., McMullin, D., Chamberlin, P., Berthiaume, G., Bailey, S., Fuller-Rowell, T., Sojka, J., Tobiska, W. K., & Viereck, R. 2011, Sol. Phys.

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