Sharp Alfvenic impulses in the near-Sun solar wind

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Title: Sharp Alfvenic impulses in the near-Sun solar wind
Authors: Horbury, T
Woolley, T
Laker, R
Matteini, L
Eastwood, J
Bale, SD
Velli, M
Chandran, BDG
Phan, T
Raouafi, NE
Goetz, K
Harvey, PR
Pulupa, M
Klein, KG
De Wit, TD
Kasper, JC
Korreck, KE
Case, AW
Stevens, ML
Whittlesey, P
Larson, D
MacDowall, RJ
Malaspina, DM
Livi, R
Item Type: Journal Article
Abstract: Measurements of the near-Sun solar wind by Parker Solar Probe have revealed the presence of largenumbers of discrete Alfv ́enic impulses with an anti-Sunward sense of propagation. These are similarto those previously observed near 1 AU, in high speed streams over the Sun’s poles and at 60 solarradii. At 35 solar radii, however, they are typically shorter and sharper than seen elsewhere. Inaddition, these spikes occur in “patches” and there are also clear periods within the same stream whenthey do not occur; the timescale of these patches might be related to the rate at which the spacecraftmagnetic footpoint tracks across the coronal hole from which the plasma originated. While the velocityfluctuations associated with these spikes are typically under 100 km/s, due to the rather low Alfv ́enspeeds in the streams observed by the spacecraft to date, these are still associated with large angulardeflections of the magnetic field - and these deflections are not isotropic. These deflections do notappear to be related to the recently reported large scale, pro-rotation solar wind flow. Estimates ofthe size and shape of the spikes reveal high aspect ratio flow-aligned structures with a transverse scaleof≈104km. These events might be signatures of near-Sun impulsive reconnection events.
Date of Acceptance: 13-Dec-2019
ISSN: 0004-637X
Publisher: American Astronomical Society
Journal / Book Title: The Astrophysical Journal: an international review of astronomy and astronomical physics
Copyright Statement: This paper is embargoed until publication.
Sponsor/Funder: Science and Technology Facilities Council (STFC)
Funder's Grant Number: ST/S000364/1
Keywords: Astronomy & Astrophysics
0201 Astronomical and Space Sciences
0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
0306 Physical Chemistry (incl. Structural)
Publication Status: Accepted
Embargo Date: publication subject to indefinite embargo
Appears in Collections:Space and Atmospheric Physics
Faculty of Natural Sciences

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