Secondary Islands in Sweet-Parker Reconnection: Scaling, Onset, and Impact on Coronal Energy Storage

Details Secondary Islands in Sweet-Parker Reconnection: Scaling, Onset, and Impact on Coronal Energy Storage Secondary Islands in Sweet-Parker Reconnection: Scaling, Onset, and Impact on Coronal Energy Storage

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh23a1531c&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SH23A-1531

Astronomy and Astrophysics

Astrophysics

[7509] Solar Physics, Astrophysics, And Astronomy / Corona, [7513] Solar Physics, Astrophysics, And Astronomy / Coronal Mass Ejections, [7519] Solar Physics, Astrophysics, And Astronomy / Flares, [7526] Solar Physics, Astrophysics, And Astronomy / Magnetic Reconnection

Scientific paper

At high Lundquist numbers, Sweet-Parker (collisional) magnetic reconnection is modified by the presence of secondary islands. It is widely accepted that this makes the reconnection faster, but how much faster is currently unknown. Is it fast enough to explain energy release in impulsive solar flares or does it remain much slower? If it becomes fast, how does magnetic energy accumulate before these events? We contribute two results using numerical simulations and scaling arguments. (1) During suitably quasi-steady temporal evolution, the reconnection rate is faster by the square root of the number of islands, in agreement with a recent model [Daughton et al., Phys. Rev. Lett., 103, 065004 (2009)]. While the scaling of the number of islands is currently unknown, models [e.g., Loureiro et al., Phys. Plasmas, 14, 100703 (2007)] predict that the number of islands scales with a small power of the Lundquist number. If this is the case, we show that the reconnection rate with secondary islands remains many orders of magnitude slower than energy release times in flares. (2) Reconnection in the corona is likely embedded, meaning the diffusion region is on a much smaller scale than the macroscopic current sheet. We show this effect has a strong impact on the condition at which secondary islands begin, in addition to slowing the reconnection and broadening the diffusion region relative to predictions using the macroscopic magnetic field. This effect, therefore, postpones the onset of fast reconnection, which allows magnetic energy more time to accumulate. We apply these scaling results to characteristic impulsive flares in the Sun, delineating observable quantities as a function of the scaling of the number of secondary islands with Lundquist number.

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