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Kasper JC, Bale SD, Belcher JW, Berthomier M, Case AW, Chandran BDG, Curtis DW, Gallagher D, Gary SP, Golub L, Halekas JS, Ho GC, Horbury TS, Hu Q, Huang J, Klein KG, Korreck KE, Larson DE, Livi R, Maruca B, Lavraud B, Louarn P, Maksimovic M, Martinovic M, McGinnis D, Pogorelov NV, Richardson JD, Skoug RM, Steinberg JT, Stevens ML, Szabo A, Velli M, Whittlesey PL, Wright KH, Zank GP, MacDowall RJ, McComas DJ, McNutt RL, Pulupa M, Raouafi NE, Schwadron NA. Alfvénic velocity spikes and rotational flows in the near-Sun solar wind. Nature 2019; 576:228-231. [PMID: 31802006 DOI: 10.1038/s41586-019-1813-z] [Citation(s) in RCA: 216] [Impact Index Per Article: 43.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Accepted: 10/17/2019] [Indexed: 11/09/2022]
Abstract
The prediction of a supersonic solar wind1 was first confirmed by spacecraft near Earth2,3 and later by spacecraft at heliocentric distances as small as 62 solar radii4. These missions showed that plasma accelerates as it emerges from the corona, aided by unidentified processes that transport energy outwards from the Sun before depositing it in the wind. Alfvénic fluctuations are a promising candidate for such a process because they are seen in the corona and solar wind and contain considerable energy5-7. Magnetic tension forces the corona to co-rotate with the Sun, but any residual rotation far from the Sun reported until now has been much smaller than the amplitude of waves and deflections from interacting wind streams8. Here we report observations of solar-wind plasma at heliocentric distances of about 35 solar radii9-11, well within the distance at which stream interactions become important. We find that Alfvén waves organize into structured velocity spikes with duration of up to minutes, which are associated with propagating S-like bends in the magnetic-field lines. We detect an increasing rotational component to the flow velocity of the solar wind around the Sun, peaking at 35 to 50 kilometres per second-considerably above the amplitude of the waves. These flows exceed classical velocity predictions of a few kilometres per second, challenging models of circulation in the corona and calling into question our understanding of how stars lose angular momentum and spin down as they age12-14.
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Affiliation(s)
- J C Kasper
- Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA. .,Smithsonian Astrophysical Observatory, Cambridge, MA, USA.
| | - S D Bale
- Physics Department, University of California, Berkeley, CA, USA.,Space Sciences Laboratory, University of California, Berkeley, CA, USA.,The Blackett Laboratory, Imperial College London, London, UK
| | - J W Belcher
- Kavli Center for Astrophysics and Space Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - M Berthomier
- Laboratoire de Physique des Plasmas, CNRS, Sorbonne Université, Ecole Polytechnique, Observatoire de Paris, Université Paris-Saclay, Paris, France
| | - A W Case
- Smithsonian Astrophysical Observatory, Cambridge, MA, USA
| | - B D G Chandran
- Department of Physics and Astronomy, University of New Hampshire, Durham, NH, USA.,Space Science Center, University of New Hampshire, Durham, NH, USA
| | - D W Curtis
- Space Sciences Laboratory, University of California, Berkeley, CA, USA
| | - D Gallagher
- Heliophysics and Planetary Science Branch ST13, Marshall Space Flight Center, Huntsville, AL, USA
| | - S P Gary
- Los Alamos National Laboratory, Los Alamos, NM, USA
| | - L Golub
- Smithsonian Astrophysical Observatory, Cambridge, MA, USA
| | - J S Halekas
- Department of Physics and Astronomy, University of Iowa, IA, USA
| | - G C Ho
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - T S Horbury
- The Blackett Laboratory, Imperial College London, London, UK
| | - Q Hu
- Department of Space Science and Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL, USA
| | - J Huang
- Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI, USA
| | - K G Klein
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA.,Department of Planetary Sciences, University of Arizona, Tucson, AZ, USA
| | - K E Korreck
- Smithsonian Astrophysical Observatory, Cambridge, MA, USA
| | - D E Larson
- Space Sciences Laboratory, University of California, Berkeley, CA, USA
| | - R Livi
- Space Sciences Laboratory, University of California, Berkeley, CA, USA
| | - B Maruca
- Department of Physics and Astronomy, University of Delaware, Newark, DE, USA.,Bartol Research Institute, University of Delaware, Newark, DE, USA
| | - B Lavraud
- Institut de Recherche en Astrophysique et Planétologie, CNRS, UPS, CNES, Université de Toulouse, Toulouse, France
| | - P Louarn
- Institut de Recherche en Astrophysique et Planétologie, CNRS, UPS, CNES, Université de Toulouse, Toulouse, France
| | - M Maksimovic
- LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
| | - M Martinovic
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
| | - D McGinnis
- Department of Physics and Astronomy, University of Iowa, IA, USA
| | - N V Pogorelov
- Department of Space Science and Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL, USA
| | - J D Richardson
- Kavli Center for Astrophysics and Space Sciences, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - R M Skoug
- Los Alamos National Laboratory, Los Alamos, NM, USA
| | | | - M L Stevens
- Smithsonian Astrophysical Observatory, Cambridge, MA, USA
| | - A Szabo
- NASA/Goddard Space Flight Center, Greenbelt, MD, USA
| | - M Velli
- Department of Earth, Planetary and Space Sciences, University of California, Los Angeles, CA, USA
| | - P L Whittlesey
- Space Sciences Laboratory, University of California, Berkeley, CA, USA
| | - K H Wright
- Universities Space Research Association, Science and Technology Institute, Huntsville, AL, USA
| | - G P Zank
- Department of Space Science and Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL, USA
| | - R J MacDowall
- NASA/Goddard Space Flight Center, Greenbelt, MD, USA
| | - D J McComas
- Department of Astrophysical Sciences, Princeton University, Princeton, NJ, USA
| | - R L McNutt
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - M Pulupa
- Space Sciences Laboratory, University of California, Berkeley, CA, USA
| | - N E Raouafi
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
| | - N A Schwadron
- Department of Physics and Astronomy, University of New Hampshire, Durham, NH, USA.,Space Science Center, University of New Hampshire, Durham, NH, USA
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Forsyth C, Fazakerley AN, Rae IJ, J Watt CE, Murphy K, Wild JA, Karlsson T, Mutel R, Owen CJ, Ergun R, Masson A, Berthomier M, Donovan E, Frey HU, Matzka J, Stolle C, Zhang Y. In situ spatiotemporal measurements of the detailed azimuthal substructure of the substorm current wedge. J Geophys Res Space Phys 2014; 119:927-946. [PMID: 26167439 PMCID: PMC4497475 DOI: 10.1002/2013ja019302] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/12/2013] [Accepted: 01/13/2014] [Indexed: 06/01/2023]
Abstract
UNLABELLED The substorm current wedge (SCW) is a fundamental component of geomagnetic substorms. Models tend to describe the SCW as a simple line current flowing into the ionosphere toward dawn and out of the ionosphere toward dusk, linked by a westward electrojet. We use multispacecraft observations from perigee passes of the Cluster 1 and 4 spacecraft during a substorm on 15 January 2010, in conjunction with ground-based observations, to examine the spatial structuring and temporal variability of the SCW. At this time, the spacecraft traveled east-west azimuthally above the auroral region. We show that the SCW has significant azimuthal substructure on scales of 100 km at altitudes of 4000-7000 km. We identify 26 individual current sheets in the Cluster 4 data and 34 individual current sheets in the Cluster 1 data, with Cluster 1 passing through the SCW 120-240 s after Cluster 4 at 1300-2000 km higher altitude. Both spacecraft observed large-scale regions of net upward and downward field-aligned current, consistent with the large-scale characteristics of the SCW, although sheets of oppositely directed currents were observed within both regions. We show that the majority of these current sheets were closely aligned to a north-south direction, in contrast to the expected east-west orientation of the preonset aurora. Comparing our results with observations of the field-aligned current associated with bursty bulk flows (BBFs), we conclude that significant questions remain for the explanation of SCW structuring by BBF-driven "wedgelets." Our results therefore represent constraints on future modeling and theoretical frameworks on the generation of the SCW. KEY POINTS The substorm current wedge (SCW) has significant azimuthal structureCurrent sheets within the SCW are north-south alignedThe substructure of the SCW raises questions for the proposed wedgelet scenario.
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Affiliation(s)
- C Forsyth
- Mullard Space Science Laboratory, UCL Dorking, UK
| | | | - I J Rae
- Mullard Space Science Laboratory, UCL Dorking, UK
| | - C E J Watt
- Department of Meteorology, University of Reading Reading, UK
| | - K Murphy
- University of Alberta Edmonton, Alberta, Canada
| | - J A Wild
- Lancaster University Lancaster, UK
| | - T Karlsson
- Royal Institute of Technology Stockholm, Sweden
| | - R Mutel
- Department of Physics and Astronomy, University of Iowa Iowa City, Iowa, USA
| | - C J Owen
- Mullard Space Science Laboratory, UCL Dorking, UK
| | - R Ergun
- LASP, University of Colorado Boulder Boulder, Colorado, USA
| | - A Masson
- ESA/ESTEC Noordwijk, Netherlands
| | - M Berthomier
- Laboratoire de Physique des Plasmas, Observatoire de Saint Maur Paris, France
| | - E Donovan
- Department of Physics and Astronomy, University of Calgary Calgary, Alberta, Canada
| | - H U Frey
- Space Sciences Laboratory, University of California Berkeley, California, USA
| | - J Matzka
- National Space Institute, Technical University of Denmark Lyngby, Denmark
| | - C Stolle
- National Space Institute, Technical University of Denmark Lyngby, Denmark ; GFZ, German Centre for Geosciences Potsdam, Germany
| | - Y Zhang
- John Hopkins University Applied Physics Laboratory Laurel, Maryland, USA
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