VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au
We report observations by the Voyager 1 and 2 spacecraft of low-frequency magnetic waves excited by newborn interstellar pickup ions H⁺ and He⁺ during 1978–1979 when the spacecraft were in the range from 2 to 6.3 au. The waves have the expected association with the cyclotron frequency of the source...
| Main Authors: | , , , , , , , , , |
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| Other Authors: | |
| Format: | Article |
| Language: | en_US |
| Published: |
IOP Publishing
2016
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| Online Access: | http://hdl.handle.net/1721.1/104969 |
| _version_ | 1826200302344208384 |
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| author | Aggarwal, Poornima Taylor, David K. Smith, Charles W. Joyce, Colin J. Fisher, Meghan K. Isenberg, Philip A. Vasquez, Bernard J. Schwadron, Nathan A. Cannon, Bradford E. Richardson, John D. |
| author2 | MIT Kavli Institute for Astrophysics and Space Research |
| author_facet | MIT Kavli Institute for Astrophysics and Space Research Aggarwal, Poornima Taylor, David K. Smith, Charles W. Joyce, Colin J. Fisher, Meghan K. Isenberg, Philip A. Vasquez, Bernard J. Schwadron, Nathan A. Cannon, Bradford E. Richardson, John D. |
| author_sort | Aggarwal, Poornima |
| collection | MIT |
| description | We report observations by the Voyager 1 and 2 spacecraft of low-frequency magnetic waves excited by newborn interstellar pickup ions H⁺ and He⁺ during 1978–1979 when the spacecraft were in the range from 2 to 6.3 au. The waves have the expected association with the cyclotron frequency of the source ions, are left-hand polarized in the spacecraft frame, and have minimum variance directions that are quasi-parallel to the local mean magnetic field. There is one exception to this in that one wave event that is excited by pickup H+ is right-hand polarized in the spacecraft frame, but similar exceptions have been reported by Cannon et al. and remain unexplained. We apply the theory of Lee & Ip that predicts the energy spectrum of the waves and then compare growth rates with turbulent cascade rates under the assumption that turbulence acts to destroy the enhanced wave activity and transport the associated energy to smaller scales where dissipation heats the background plasma. As with Cannon et al., we find that the ability to observe the waves depends on the ambient turbulence being weak when compared with growth rates, thereby allowing sustained wave growth. This analysis implies that the coupled processes of pitch-angle scattering and wave generation are continuously associated with newly ionized pickup ions, despite the fact that the waves themselves may not be directly observable. When waves are not observed, but wave excitation can be argued to be present, the wave energy is simply absorbed by the turbulence at a rate that prevents significant accumulation. In this way, the kinetic process of wave excitation by scattering of newborn ions continues to heat the plasma without producing observable wave energy. These findings support theoretical models that invoke efficient scattering of new pickup ions, leading to turbulent driving in the outer solar wind and in the IBEX ribbon beyond the heliopause. |
| first_indexed | 2024-09-23T11:34:23Z |
| format | Article |
| id | mit-1721.1/104969 |
| institution | Massachusetts Institute of Technology |
| language | en_US |
| last_indexed | 2024-09-23T11:34:23Z |
| publishDate | 2016 |
| publisher | IOP Publishing |
| record_format | dspace |
| spelling | mit-1721.1/1049692022-09-27T20:27:32Z VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au Aggarwal, Poornima Taylor, David K. Smith, Charles W. Joyce, Colin J. Fisher, Meghan K. Isenberg, Philip A. Vasquez, Bernard J. Schwadron, Nathan A. Cannon, Bradford E. Richardson, John D. MIT Kavli Institute for Astrophysics and Space Research Richardson, John D We report observations by the Voyager 1 and 2 spacecraft of low-frequency magnetic waves excited by newborn interstellar pickup ions H⁺ and He⁺ during 1978–1979 when the spacecraft were in the range from 2 to 6.3 au. The waves have the expected association with the cyclotron frequency of the source ions, are left-hand polarized in the spacecraft frame, and have minimum variance directions that are quasi-parallel to the local mean magnetic field. There is one exception to this in that one wave event that is excited by pickup H+ is right-hand polarized in the spacecraft frame, but similar exceptions have been reported by Cannon et al. and remain unexplained. We apply the theory of Lee & Ip that predicts the energy spectrum of the waves and then compare growth rates with turbulent cascade rates under the assumption that turbulence acts to destroy the enhanced wave activity and transport the associated energy to smaller scales where dissipation heats the background plasma. As with Cannon et al., we find that the ability to observe the waves depends on the ambient turbulence being weak when compared with growth rates, thereby allowing sustained wave growth. This analysis implies that the coupled processes of pitch-angle scattering and wave generation are continuously associated with newly ionized pickup ions, despite the fact that the waves themselves may not be directly observable. When waves are not observed, but wave excitation can be argued to be present, the wave energy is simply absorbed by the turbulence at a rate that prevents significant accumulation. In this way, the kinetic process of wave excitation by scattering of newborn ions continues to heat the plasma without producing observable wave energy. These findings support theoretical models that invoke efficient scattering of new pickup ions, leading to turbulent driving in the outer solar wind and in the IBEX ribbon beyond the heliopause. University of New Hampshire (Caltech subcontract 44A1085631) United States. National Aeronautics and Space Administration (grant NNX13AF97G) United States. National Aeronautics and Space Administration (grant NNX11AJ37G) National Science Foundation (U.S.) (grant AGS0962506) National Science Foundation (U.S.) (grant AGS1357893) 2016-10-25T16:14:44Z 2016-10-25T16:14:44Z 2016-05 2016-01 Article http://purl.org/eprint/type/JournalArticle 1538-4357 0004-637X http://hdl.handle.net/1721.1/104969 Aggarwal, Poornima, David K. Taylor, Charles W. Smith, Colin J. Joyce, Meghan K. Fisher, Philip A. Isenberg, Bernard J. Vasquez, Nathan A. Schwadron, Bradford E. Cannon, and John D. Richardson. “VOYAGEROBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 Au.” The Astrophysical Journal vol. 822, no. 2, 94, May 2016, pp. 1-13. © 2016. The American Astronomical Society. en_US http://dx.doi.org/10.3847/0004-637X/822/2/94 Astrophysical Journal Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use. application/pdf IOP Publishing American Astronomical Society |
| spellingShingle | Aggarwal, Poornima Taylor, David K. Smith, Charles W. Joyce, Colin J. Fisher, Meghan K. Isenberg, Philip A. Vasquez, Bernard J. Schwadron, Nathan A. Cannon, Bradford E. Richardson, John D. VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au |
| title | VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au |
| title_full | VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au |
| title_fullStr | VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au |
| title_full_unstemmed | VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au |
| title_short | VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au |
| title_sort | voyager observations of magnetic waves due to newborn interstellar pickup ions 2 6 au |
| url | http://hdl.handle.net/1721.1/104969 |
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