Letter to the Editor

A nanoflare model for active region radiance: application of artificial neural networks

¹ IUCAA, Post Bag 4, Ganeshkhind, Pune 411 007, India
² Institute for Advanced Studies in Basic Sciences, Zanjan, Iran
³ Max-Planck Institut für Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany e-mail: innes@mps.mpg.de
⁴ Department of Physics, Zanjan University, Zanjan, Iran
⁵ Department of Electronics Science, University of Pune, Pune 411007, India

Received: 4 September 2008
Accepted: 22 October 2008

Abstract

Context. Nanoflares are small impulsive bursts of energy that blend with and possibly make up much of the solar background emission. Determining their frequency and energy input is central to understanding the heating of the solar corona. One method is to extrapolate the energy frequency distribution of larger individually observed flares to lower energies. Only if the power law exponent is greater than 2 is it considered possible that nanoflares contribute significantly to the energy input.

Aims. Time sequences of ultraviolet line radiances observed in the corona of an active region are modelled with the aim of determining the power law exponent of the nanoflare energy distribution.

Methods. A simple nanoflare model based on three key parameters (the flare rate, the flare duration, and the power law exponent of the flare energy frequency distribution) is used to simulate emission line radiances from the ions Fe, Ca, and , observed by SUMER in the corona of an active region as it rotates around the east limb of the Sun. Light curve pattern recognition by an Artificial Neural Network (ANN) scheme is used to determine the values.

Results. The power law exponents, , 2.8, and 2.6 are obtained for Fe, Ca, and  respectively.

Conclusions. The light curve simulations imply a power law exponent greater than the critical value of 2 for all ion species. This implies that if the energy of flare-like events is extrapolated to low energies, nanoflares could provide a significant contribution to the heating of active region coronae.