The Topology of Magnetic Reconnection in Solar Flares

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62lifetime. For this study, we chose flares whose footpoints did not move because we wantedto be able to associate flares and separators without introducing undue complexity. Theproperties of the three flares are given in Table 4.1.The two most commonly used RHESSI image reconstruction algorithims are Clean(Högbom, 1974; Hurford et al., 2002) and Pixon (Puetter, 1995; Hurford et al., 2002).Clean is an iterative reconstruction algorithm that is quick and often satisfactorally representsboth point and extended sources. For these reasons, we used Clean to make theimages analyzed in flares B and C. Occasionally, the Clean algorithm does not removeenough noise from an image such that the morphology of the sources is not clear. In someof these cases, the Pixon algorithm, which has superior noise reduction and photometry,can result in an image with sufficently defined sources. While Pixon gives superior images,it is significantly more time consuming than Clean. For this reason, it is typically not thefirst choice for exploring HXR sources observed by RHESSI. Due to the low number ofcounts available for making an image of the footpoints of flare A, the two sources couldnot be distinguished from one another at the 30% level of the Clean image. Therefore, weuse a Pixon image in this case.The first flare, hereafter flare A, occurred on 26 February 2004. As can be seen inFigure 4.1, this flare was a GOES X1 class flare that had an impulsive phase lasting onlya few minutes. The small peak in the RHESSI 50-100 keV emission around 01:54:30UT is the only time it was possible to make an image of the HXR sources in this energyrange. Detailed spectroscopic analysis of the flare has shown that the 25-50 keV countsafter about 01:58 UT are primarily thermal in nature. The contours used to classify theflaring separators for flare A are drawn at the 20% level of a 30-100 keV Pixon image.The image, shown in Figure 4.2, was made by summing the counts in detectors 1-9 from01:54:40-01:55:00 UT in the 30-100 keV range.The second flare, hereafter flare B, took place on 6 April 2004. Flare B, an M2 class
63Figure 4.1: GOES and RHESSI light curves. Dashed lines in the left panels mark the timerange for the right panels. The right hand panels are corrected RHESSI light curves, wherethe effects of attenuator and decimation state changes are accounted for. The 6-12 keVcurves are light grey, 25-50 keV are dark grey and 50-100 keV are black. Solid verticallines mark the time range over which the RHESSI images used in Figures 4.2 and 4.3 wereintegrated.
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THE TOPOLOGY OF MAGNETIC RECONNECTI
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iiAPPROVALof a dissertation submitt
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ivTo Liebe -I’m the lucky one
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viiLIST OF TABLESTablePage2.1 Flare
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ix2.3 Left hand panels are GOES lig
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xiABSTRACTIn order to better unders
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2The release of this large amount o
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5100.000RHESSI Count Flux vs Energy
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7excitation in the chromosphere.The
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9one day before the two large X-cla
Page 23 and 24: 11of well-defined features like sun
Page 25 and 26: 13introduced (i.e. Titov et al., 20
Page 27 and 28: 15CHAPTER 2RECONNECTION IN THREE DI
Page 29 and 30: 17spine lines.In this Chapter, for
Page 31 and 32: 19Table 2.1: Flare properties. AR i
Page 33 and 34: 21-300A) TRACE 195, RHESSI 50-100 k
Page 35 and 36: 23Figure 2.3: Left hand panels are
Page 37 and 38: 25the same time. With a 20 s imagin
Page 39 and 40: 27sheared or twisted flux tubes, wh
Page 41 and 42: 29Figure 2.4: Top: photospheric foo
Page 43 and 44: 31track 2 to 3 and from track 3 to
Page 45 and 46: 33error. If we had simply fit the f
Page 47 and 48: 3512 23 31Figure 2.6: Upper panel:
Page 49 and 50: 37In case 1, we suppose that the do
Page 51 and 52: 39null which shifts during the flar
Page 53 and 54: 41tiation and evolution. Further wo
Page 55 and 56: 43photospheric and coronal magnetic
Page 57 and 58: 45Here, B z (x,y) is the value of t
Page 59 and 60: 47been determined, several other to
Page 61 and 62: 49Figure 3.1: Simulated magnetogram
Page 63 and 64: 51Figure 3.3: Same as Figure 3.1, b
Page 65 and 66: 53MDI 6 Apr 2004, 12:51 UT-120-140-
Page 67 and 68: 55of new field and horizontal flows
Page 69 and 70: 57arators (Henoux and Somov, 1987).
Page 71 and 72: 59the line-tied nature of the photo
Page 73: 61a snapshot in time (Démoulin, 20
Page 77 and 78: 65order to take advantage of the av
Page 79 and 80: 67field lines or sheared or twisted
Page 81 and 82: 69Flare A, MDI 01:39 UT400438350256
Page 83 and 84: 71flux discrepancy∆Φ r = −∆t
Page 85 and 86: 73Flare A, RHESSI 30-100 keV4004383
Page 87 and 88: 75(in the form of heating and parti
Page 89 and 90: 77CHAPTER 5DISCUSSION AND CONCLUSIO
Page 91 and 92: 79separator (nulls) are along spine
Page 93 and 94: 81emission is concentrated in compa
Page 95 and 96: 83REFERENCESAulanier, G., P. Démou
Page 97 and 98: 85Meyer, S. J. Morrison, M. D. Morr
Page 99 and 100: 87Priest, E., and T. Forbes, Magnet
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The Topology of Magnetic Reconnection in Solar Flares

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