Unveiling the magnetic nature of chromospheric vortices^⋆

¹ INAF Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Roma, 00078 Monte Porzio Catone, RM, Italy
e-mail: mariarita.murabito@inaf.it
² The Centre for Fusion, Space and Astrophysics, Department of Physics, University of Warwick, Coventry CV4 7AL, UK
³ Armagh Observatory and Planetarium, College Hill, Armagh BT61 9DB, UK
⁴ ASI – Agenzia Spaziale Italiana, Via del Politecnico snc, Rome, Italy

Received: 5 May 2020
Accepted: 12 June 2020

Abstract

Context. Vortex structures in the Sun’s chromosphere are believed to channel energy between different layers of the solar atmosphere.

Aims. We investigate the nature and dynamics of two small-scale quiet-Sun rotating structures in the chromosphere.

Methods. We analysed two chromospheric structures that show clear rotational patterns in spectropolarimetric observations taken with the Interferometric Bidimensional Spectrometer at the Ca II 8542 Å line.

Results. We present the detection of spectropolarimetric signals that manifest the magnetic nature of rotating structures in the chromosphere. Our observations show two long-lived structures of plasma that each rotate clockwise inside a 10 arcsec² quiet-Sun region. Their circular polarisation signals are five to ten times above the noise level. Line-of-sight Doppler velocity and horizontal velocity maps from the observations reveal clear plasma flows at and around the two structures. A magnetohydrodynamics simulation shows these two structures are plausibly magnetically connected. Wave analysis suggests that the observed rotational vortex pattern could be due to a combination of slow actual rotation and a faster azimuthal phase speed pattern of a magnetoacoustic mode.

Conclusions. Our results imply that the vortex structures observed in the Sun’s chromosphere are magnetic in nature and that they can be connected locally through the chromosphere