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The angular-momentum flux in the solar wind observed during Solar Orbiter's first orbit

Verscharen, D; Stansby, D; Finley, AJ; Owen, CJ; Horbury, T; Maksimovic, M; Velli, M; ... al, E; + view all (2021) The angular-momentum flux in the solar wind observed during Solar Orbiter's first orbit. Astronomy & Astrophysics , 656 , Article A28. 10.1051/0004-6361/202140956. Green open access

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Abstract

Aims: We present the first measurements of the angular-momentum flux in the solar wind recorded by the Solar Orbiter spacecraft. Our aim is to validate these measurements to support future studies of the Sun’s angular-momentum loss. Methods: We combined 60-min averages of the proton bulk moments and the magnetic field measured by the Solar Wind Analyser (SWA) and the magnetometer (MAG) onboard Solar Orbiter. We calculated the angular-momentum flux per solid-angle element using data from the first orbit of the mission’s cruise phase in 2020. We separated the contributions from protons and from magnetic stresses to the total angular-momentum flux. Results: The angular-momentum flux varies significantly over time. The particle contribution typically dominates over the magneticfield contribution during our measurement interval. The total angular-momentum flux shows the largest variation and is typically anticorrelated with the radial solar-wind speed. We identify a compression region, potentially associated with a co-rotating interaction region or a coronal mass ejection, which leads to a significant localised increase in the angular-momentum flux, albeit without a significant increase in the angular momentum per unit mass. We repeated our analysis using the density estimate from the Radio and Plasma Waves (RPW) instrument. Using this independent method, we find a decrease in the peaks of positive angular-momentum flux, but otherwise, our results remain consistent. Conclusions: Our results largely agree with previous measurements of the solar wind’s angular-momentum flux in terms of amplitude, variability, and dependence on radial solar-wind bulk speed. Our analysis highlights the potential for more detailed future studies of the solar wind’s angular momentum and its other large-scale properties with data from Solar Orbiter. We emphasise the need for studying the radial evolution and latitudinal dependence of the angular-momentum flux in combination with data from Parker Solar Probe and other assets at heliocentric distances of 1 au and beyond.

Type: Article
Title: The angular-momentum flux in the solar wind observed during Solar Orbiter's first orbit
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/202140956
Publisher version: https://doi.org/10.1051/0004-6361/202140956
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Magnetohydrodynamics (MHD) – Plasmas – Sun: magnetic fields – solar wind – Stars: rotation
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10132058
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