Letter to the Editor

The dynamics of small-scale magnetic fields modulated by the solar cycle

¹ ASI Italian Space Agency, Via del Politecnico snc, 00133 Rome, Italy
² Plasma Dynamics Group, School of Mathematical and Physical Sciences, The University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK
³ Plasma Dynamics Group, School of Electrical and Electronic Engineering, The University of Sheffield, Mappin Street, Sheffield S1 3JD, UK
⁴ University of Trento, Via Calepina 14, 38122 Trento, Italy
⁵ University of Rome Tor Vergata, Department of Physics, Via della Ricerca Scientifica 3, 00133 Rome, Italy
⁶ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
⁷ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast, BT7 1NN,Northern Ireland, UK
⁸ Niels Bohr International Academy, Niels Bohr Institute, Blegdamsvej 17, DK-2100 Copenhagen, Denmark
⁹ Department of Physics and Astronomy, California State University Northridge, Northridge, CA 91330, USA
¹⁰ INGV, Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
¹¹ INAF-IAPS, Istituto Nazionale di Astrofisica, Rome, Italy

^⋆ Corresponding author; marco.stangalini@asi.it

Received: 19 December 2024
Accepted: 14 February 2025

Abstract

In addition to sunspots, the most easily visualized manifestation of solar magnetism, cutting-edge observations of the solar atmosphere have uncovered a plethora of magnetic flux tubes, down to the resolving power of modern high-resolution telescopes (a few tens of kilometers), revealing how the Sun is a fully magnetized star. These magnetic elements are advected and buffeted by ambient plasma flows and turbulent convection, resulting in perturbations of the flux tubes that make them natural conduits for channeling wave energy into the upper layers of the Sun’s atmosphere and significantly contributing to the acceleration of the solar wind. Data acquired by the Helioseismic and Magnetic Imager (HMI) on board NASA’s Solar Dynamics Observatory (SDO) have made it possible to study the dynamics of small-scale magnetic fields over long timescales. Here, for the first time, we present the discovery of a modulation in the dynamical behavior of small-scale magnetic concentrations in the photosphere over temporal scales consistent with the solar activity cycle (i.e., 11 years), which has only been made possible by the long observing lifetime of the SDO/HMI spacecraft. Furthermore, we also find a temporal varying polarization of their perturbations on similar timescales. This demonstrates how the small-scale dynamics of magnetic fields are also affected by the global dynamo. These discoveries were realized through automated tracking of magnetic fields in the solar photosphere over 11 continuous years, resulting in the most extended statistical analysis of its kind so far, with more than 31 million magnetic concentrations examined.