Solar extreme ultraviolet variability as a proxy for nanoflare heating diagnostics

Space Research Institute, Profsoyuznaya 84/32, Moscow 117997, Russia
e-mail: artem.ulianov@gmail.com

Received: 30 October 2023
Accepted: 16 December 2023

Abstract

Aims. We aim to improve the existing techniques to probe the nanoflare hypothesis for the coronal heating problem. For this purpose, we propose using the solar extreme ultraviolet (EUV) emission variability registered with modern space-based imagers.

Methods. We followed a novel model-based approach. As a starting point, we used the EBTEL 0d hydrodynamic model. We integrated the arising system of stochastic differential equations to calculate the covariance matrix for plasma parameters. We then employed a Taylor expansion technique to relate model parameters with observable EUV intensity variation statistics.

Results. We found that in the high-frequency approximation, the variability of the EUV emission is defined by the dimensionless factor ϖ, which is inversely proportional to the frequency. We calculated the factor ϖ throughout the solar disk and found that it does not exceed 0.01, except for the finite number of compact regions. The distribution of ϖ follows the power law with an index of ≈ − 2.6. To validate our approach, we used it to probe the temperature of the coronal plasma. We show that the line-of-sight temperature distribution is close to homogeneous with a mode of ≈1.25 MK, which is in perfect agreement with the results of the spectroscopic diagnostics.