Near-continuous tracking of solar active region NOAA 13664 over three solar rotations

¹ ETH Zürich, Institute for Particle Physics and Astrophysics, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland
² Istituto Ricerche Solari Aldo e Cele Daccò (IRSOL), Faculty of Informatics, Università della Svizzera Italiana, CH-6605 Locarno, Switzerland
³ PMOD/WRC, Dorfstrasse 33, 7260 Davos Dorf, Switzerland
⁴ University of Applied Sciences and Arts Northwestern Switzerland, Bahnhofstrasse 6, 5210 Windisch, Switzerland
⁵ University College London, Mullard Space Science Laboratory, Holmbury St Mary, Dorking Surrey RH5 6NT, UK
⁶ University of Vienna, Institute of Astrophysics, Türkenschanzstrasse 17, Vienna A-1180, Austria
⁷ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37077 Göttingen, Germany
⁸ Euler Institute, Faculty of Informatics, Università Svizzera Italiana, Lugano, Switzerland

^⋆ Corresponding author: ikontogianni@phys.ethz.ch

Received: 27 June 2025
Accepted: 3 October 2025

Abstract

Context. Magnetic flux emergence and decay in the Sun are processes that can span from days to months. However, their tracking is typically limited to about half a solar rotation when relying on single-vantage-point observations, providing only a partial view of the phenomenon.

Aims. This study aims to monitor the magnetic and coronal evolution and characterize the non-potentiality of the solar active region NOAA 13664, one of the most complex and eruptive regions of the past two decades, over more than three full solar rotations, by combining observations from both the Earth-facing side of the Sun and the far side.

Methods. We used photospheric magnetograms and extreme-ultraviolet (EUV) filtergrams from Solar Orbiter and the Solar Dynamics Observatory, taken continuously over a 94 day period, along with 969 flare detections from combining the Geostationary Operational Environmental Satellite and the Spectrometer/Telescope for Imaging X-rays instrument on board the Solar Orbiter. All images were deprojected into a common coordinate system and merged into a unified dataset. We tracked the evolution of magnetic flux and EUV emission and computed magnetic field parameters from the line-of-sight magnetograms to quantify the region’s non-potentiality. The latter comprise the first continuous time series of their kind.

Results. We successfully identified the region’s initial emergence and followed its evolution through to its decay. The region developed through successive flux emergence episodes over a period of 20 days, reached its peak complexity one month after the first emergence, and gradually decayed over the following two months. Unlike many complex regions, it consistently maintained high levels of non-potentiality for most of its lifetime, sustaining equally strong flaring activity. The derived time series of non-potentiality parameters far exceeded the typical 14 day window imposed by solar rotation and were remarkably consistent, exhibiting strong correlation with the flaring activity of the region.

Conclusions. Multi-vantage-point observations offer valuable insights into the dynamics of flux emergence and decay, beyond the two-week limit imposed by solar rotation on observations along the Sun-Earth line. The corresponding combined datasets can significantly improve our understanding of how magnetic flux emerges, evolves, and drives solar activity.