Categorization model of moving small-scale intensity enhancements in solar active regions

¹ Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
e-mail: bidzina.shergelashvili@oeaw.ac.at
² Centre for Computational Helio Studies, Ilia State University, G. Tsereteli Street 3, 0162 Tbilisi, Georgia
³ Evgeni Kharadze Georgian National Astrophysical Observatory, M. Kostava Street 47/57, 0179 Tbilisi, Georgia
⁴ Capitec Bank, 5 Neutron Street, Stellenbosch 7600, South Africa
⁵ Centre for Mathematical Plasma Astrophysics/Department of Mathematics, Celestijnenlaan 200B, 3001 Leuven, Belgium
⁶ Institute of Physics, University of Maria Curie-Skłodowska, 20-031 Lublin, Poland
⁷ Institute of Astronomy, Russian Academy of Sciences, 119017 Moscow, Russia
⁸ Institute of Laser Physics SB RAS, 630090 Novosibirsk, Russia

Received: 29 October 2021
Accepted: 16 February 2022

Abstract

Context. The small-scale moving intensity enhancements remotely observed in the extreme ultraviolet images of the solar active regions, which we refer to as active region moving campfires (ARMCs), are related to local plasma temperature and/or density enhancements. Their dynamics is driven by the physical processes in the entire coronal plasma. Our previous study of ARMCs indicates that they have characteristic velocities at around the background sound speed. In the present paper, we further investigate the dynamical and statistical properties of ARMCs.

Aims. The main goal of our work is to carry out a simultaneous analysis of EUV images from two observational missions, SDO/AIA and Hi-C 2.1. The aims of the performed cross-validating analysis of both SDO/AIA and Hi-C 2.1 data were to reveal how the observed moving features are distributed over the studied active region, AR12712, and to perform a statistical hypothesis test of the existence of different groups of ARMCs with distinct physical characteristics.

Methods. We use the statistical model of intensity centroid convergence and tracking that was developed in our previous paper. Furthermore, a Gaussian mixture model fit of the observed complex of moving ARMCs is elaborated to reveal the existence of distinct ARMC groups and to study the physical characteristics of these different groups.

Results. In data from the 171 Å, 193 Å and 211 Å channels of SDO/AIA, we identified several groups of ARMCs with respect to both blob intensity and velocity profiles. The existence of such groups is confirmed by the cross-validation of the 172 Å data sets from Hi-C 2.1.

Conclusions. The ARMCs studied in this paper have characteristic velocities in the range of the typical sound speeds in coronal loops. Hence, these moving objects differ from the well-known rapid Alfvénic velocity jets from magnetic reconnection sites. This is also proven by the fact that ARMCs propagate along the active region magnetic structure (strands). The nature of the discovered statistical grouping of the ARMC events is not known. Further theoretical studies and modeling is required to reveal this nature.