Solar Orbiter observations of an ion-scale flux rope confined to a bifurcated solar wind current sheet

¹ The Blackett Laboratory, Imperial College London, Exhibition Road, London SW7 2AZ, UK
e-mail: jonathan.eastwood@imperial.ac.uk
² Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
³ Center for Space and Aeronomic Research (CSPAR) and Department of Space Science, The University of Alabama in Huntsville, Huntsville, AL 35899, USA
⁴ Laboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, 33615 Pessac, France
⁵ Institut de Recherche en Astrophysique et Planétologie, CNRS, CNES, Université de Toulouse, 31028 Toulouse Cedex 4, France
⁶ Bartol Research Institute, University of Delaware, Newark, DE 19716, USA
⁷ Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA

Received: 31 March 2021
Accepted: 18 August 2021

Abstract

Context. Flux ropes in the solar wind are a key element of heliospheric dynamics and particle acceleration. When associated with current sheets, the primary formation mechanism is magnetic reconnection and flux ropes in current sheets are commonly used as tracers of the reconnection process.

Aims. Whilst flux ropes associated with reconnecting current sheets in the solar wind have been reported, their occurrence, size distribution, and lifetime are not well understood.

Methods. Here we present and analyse new Solar Orbiter magnetic field data reporting novel observations of a flux rope confined to a bifurcated current sheet in the solar wind. Comparative data and large-scale context is provided by Wind.

Results. The Solar Orbiter observations reveal that the flux rope, which does not span the current sheet, is of ion scale, and in a reconnection formation scenario, existed for a prolonged period of time as it was carried out in the reconnection exhaust. Wind is also found to have observed clear signatures of reconnection at what may be the same current sheet, thus demonstrating that reconnection signatures can be found separated by as much as ∼2000 Earth radii, or 0.08 au.

Conclusions. The Solar Orbiter observations provide new insight into the hierarchy of scales on which flux ropes can form, and show that they exist down to the ion scale in the solar wind. The context provided by Wind extends the spatial scale over which reconnection signatures have been found at solar wind current sheets. The data suggest the local orientations of the current sheet at Solar Orbiter and Wind are rotated relative to each other, unlike reconnection observed at smaller separations; the implications of this are discussed with reference to patchy vs. continuous reconnection scenarios.