Slow solar wind sources

High-resolution observations with a quadrature view^⋆

¹ ETH-Zurich, Hönggerberg Campus, HIT Building, Wolfgang-Pauli-Str. 27, 8093 Zürich, Switzerland
² PMOD/WRC, Dorfstrasse 33, 7260 Davos Dorf, Switzerland
e-mail: krzysztof.barczynski@pmodwrc.ch
³ Solar–Terrestrial Centre of Excellence – SIDC, Royal Observatory of Belgium, Ringlaan -3- Av. Circulaire 1180 Brussels, Belgium
⁴ Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale, 91405 Orsay, France
⁵ Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁶ UCL-Mullard Space Science Laboratory, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
⁷ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, University Road, Belfast BT7 1NN, UK
⁸ Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119992 Moscow, Russia

Received: 24 January 2023
Accepted: 22 February 2023

Abstract

Context. The origin of the slow solar wind is still an open issue. One possibility that has been suggested is that upflows at the edge of an active region can contribute to the slow solar wind.

Aims. We aim to explain how the plasma upflows are generated, which mechanisms are responsible for them, and what the upflow region topology looks like.

Methods. We investigated an upflow region using imaging data with the unprecedented temporal (3 s) and spatial (2 pixels = 236 km) resolution that were obtained on 30 March 2022 with the 174 Å channel of the Extreme-Ultraviolet Imager (EUI)/High Resolution Imager (HRI) on board Solar Orbiter. During this time, the EUI and Earth-orbiting satellites (Solar Dynamics Observatory, Hinode, and the Interface Region Imaging Spectrograph, IRIS) were located in quadrature (∼92°), which provides a stereoscopic view with high resolution. We used the Hinode/EIS (Fe XII) spectroscopic data to find coronal upflow regions in the active region. The IRIS slit-jaw imager provides a high-resolution view of the transition region and chromosphere.

Results. For the first time, we have data that provide a quadrature view of a coronal upflow region with high spatial resolution. We found extended loops rooted in a coronal upflow region. Plasma upflows at the footpoints of extended loops determined spectroscopically through the Doppler shift are similar to the apparent upward motions seen through imaging in quadrature. The dynamics of small-scale structures in the upflow region can be used to identify two mechanisms of the plasma upflow: Mechanism I is reconnection of the hot coronal loops with open magnetic field lines in the solar corona, and mechanism II is reconnection of the small chromospheric loops with open magnetic field lines in the chromosphere or transition region. We identified the locations in which mechanisms I and II work.