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R.L. Moore (NASA/MSFC), D.A. Falconer (UAH/MSFC), J.G. Porter (NASA/MSFC)
In previous work, by registering Yohkoh SXT coronal X-ray images with MSFC vector magnetograms, we found that (1) many of the larger bright coronal loops rooted at one or both ends in an active region are rooted around magnetic islands of included polarity, (2) the core field encasing the neutral line encircling the island is strongly sheared, and (3) this sheared core field is the seat of frequent microflares (Falconer et al 1997, ApJ, 482, 519; Porter et al 1998, in Solar Jets and Coronal Plumes, ed. T.-D. Guyenne (ESA SP-421), p. 147). This suggests that the coronal heating in these extended bright loops is driven by many small explosive releases of stored magnetic energy from the sheared core field at their feet, some of which magnetic microexplosions also produce the microflare heating in the core fields. In this paper, we show that this scenario is feasible in terms of the energy required for the observed coronal heating and the magnetic energy available in the observed sheared core fields. In a representative active region, from the X-ray and vector field data, we estimate the coronal heating energy consumption by a selected typical large bright loop, the coronal heating energy consumption by a typical microflare at the foot of this loop, the frequency of microflares at the foot, and the available magnetic energy in the microflaring core field. We find that (1) the rate of magnetic energy release to power the microflares at the foot (~ \times 1025 erg/s) is enough to also power the coronal heating in the body of the extended loop (~2 \times 1025 erg/s), and (2) there is enough stored magnetic energy in the sheared core field to sustain the microflaring and extended loop heating for about a day, which is a typical time for buildup of neutral-line magnetic shear in an active region. This work was funded by the Solar Physics Branch of NASA's Office of Space Science through the SR&T Program and the SEC Guest Investigator Program.
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