Period increase and amplitude modification in the kink oscillations of a small-scale EUV loop

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Solar Orbiter/EUI High Resolution Imager observations (2 s cadence) uncover the first case of simultaneous sub-minute period and amplitude growth in transverse kink oscillations at the apex of a bundle of Quiet-Sun coronal small-scale EUV loop. The event occurs in four episodes and each episode starts with both period and amplitude growth for a couple of cycles and ends with a sudden reset in both oscillation period and amplitude values. During each episode, the oscillation period increases, most plausibly due to rising density within the flux tube, as evidenced by concurrent intensity increase and theoretical expectations, while the amplitude also grows, potentially driven by a localized heating pulse or nearby activity (though verification is limited by SDO’s far-side perspective and EUI’s field-of-view) that repeats to energy injection into the standing kink wave. The observed episodic abrupt reset of the oscillation period and amplitude suggests repeated magnetic reconfiguration of the loop system, possibly driven by intermittent magnetic reconnection. The kink and Alfvén speeds, magnetic field strength, and total energy of the kink wave is estimated.

The authors thank to the anonymous reviewers for their very constructive comments to improve the manuscript. N.D. sincerely thanks to Prof. Valery Nakariakov and Dr. Daye Lim, for reading the manuscript and providing their very helpful comments. Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. The EUI instrument was built by CSL, IAS, MPS, MSSL/UCL. PMOD/WRC, ROB, LCF/IO with funding from the Belgian Federal Science Policy Office (BELSPO/PRODEX PEA 4000112292 AND 4000134088); the Centre National d’Etudes Spatiales (CNES); the UK Space Agency (UKSA); the Bundesministerium f \(\mathrm{\ddot{u}}\) r Wirtschaft und Energie (BMWi) through the Deutsches Zentrum f \(\mathrm{\ddot{u}}\) r Luft- und Raumfahrt (DLR); and the Swiss Space Office (SSO). Wavelet software was provided by C. Torrence and G. Compo, and is available at http://paos.colorado.edu/research/wavelets/ .

Department of Physics, Faculty of Science, University of Zanjan, Zanjan, Zanjan, 45371-38791, Iran

Lockheed Martin Solar and Astrophysics Laboratory, 3251 Hanover Street, Palo Alto, CA, 94306, USA

Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077, Göttingen, Germany

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( A ) Wavelet analysis of the CB oscillations. Details are described inside the text. (B, E) Wavelet analysis of the integrated intensity along the slits S1, S2, S3, and S0, between the pixel positions 20 to 30, respectively.

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Dadashi, N., Khademi, B., Tiwari, S.K. et al. Period increase and amplitude modification in the kink oscillations of a small-scale EUV loop. Sci Rep (2026). https://doi.org/10.1038/s41598-026-63427-w

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