Solar Flares: avalanche models & forecasting

LAURA MORALES

Santiago de Chile

Conferencia; XII Latin American Conference on Space Geophysics; 2021

Universidad de Chile

Solar flares are the manifestation of intermittent and impulsive release of energy in the corona.The spatial coincidence of flares with magnetic structures at the solar surface leaves no doubtthat flares draw their energy from the Sun’s magnetic field. Since they are produced veryrapidly magnetic reconnection seems to be a good fit for the physical mechanism responsiblefor extracting that energy. Observations of flares from the extreme ultraviolet to soft and hardX-rays revealed that the frequency distribution of solar flare energy release follows a welldefined power law, spanning 8 orders of magnitude in flare energy (Aschwanden, 2011 andreferences there in). In the early ’90s Lu & Hamilton incorporated Parker’s insight for coronalheating and proposed a way to explain the observed power-laws assuming that solar flares areavalanches of several reconnection events occurring in a solar coronal loop.In a previous manuscript (Morales & Charbonneau, 2008) we have designed an avalanchemodel for solar flares that uses magnetic field lines as basic dynamical elements. We assumean idealized representation of a coronal loop as a bundle of magnetic flux strands wrappingaround one another. The model operates by means of a two-dimensional cellular automatonwith anisotropic connectivity, where linear ensembles of interconnected nodes define theindividual strands collectively making up the coronal loop. The system is driven by randomdeformation of the strands. To represented magnetic reconnection we assumed that when theangle subtended by two strands crossing at the same lattice site exceed some preset thresholdis realeased. We have shown that this system produces avalanches of reconnection eventscharacterized by scale-free size distributions that compare very well with existing observations(Morales & Charbonneau, 2008 and 2009). In this work we extend the models predictingcapabilities of extreme flares by characterizing the waiting times between avalanches,particularly we study the behavior of the extreme avalanches produced and discuss the possibleimplications for flare forecasting