The Spatio-Temporal Evolution of Solar Flare Observed with AIA/SDO: Fractal Diffusion, Sub-Diffusion, or Logistic Growth ?}
Markus J. Aschwanden Submitted: 2012-08-07 15:05
We explore the spatio-temporal evolution of solar flares by fitting
a radial expansion model r(t) that consists of an exponentially
growing acceleration phase, followed by a deceleration phase that
is parameterized by the generalized diffusion function
r(t) propto kappa (t-t_1)eta/2, which
includes the logistic growth limit (eta=0), sub-diffusion
(eta = 0-1), classical diffusion (eta=1), super-diffusion
(eta = 1-2), and the linear expansion limit (eta=2).
We analyze all M and X-class flares observed with GOES and AIA/SDO
during the first two years of the SDO mission, amounting to 155 events.
We find that most flares operate in the sub-diffusive regime
(eta=0.53pm0.27), which we interpret in terms of anisotropic
chain reactions of intermittent magnetic reconnection episodes
in a low plasma-eta corona. We find a mean propagation speed of
v=15pm12 km s-1, with maximum speeds of vmax=80 pm 85
km s-1 per flare, which is substantially slower than the
sonic speeds expected for thermal diffusion of flare plasmas.
The diffusive characteristics established here (for the first time
for solar flares) is consistent with the fractal-diffusive
self-organized criticality (FD-SOC) model, which predicted
diffusive transport merely based on cellular automaton simulations.
Authors: Markus J. Aschwanden
Publication Status: ApJ Vol. 757, p.94 (2012)
Last Modified: 2012-09-11 13:42