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VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS

Title: VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2-6 au.
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Name(s): Aggarwal, Poornima, author
Taylor, David K., author
Smith, Charles W., author
Joyce, Colin J., author
Fisher, Meghan K., author
Isenberg, Philip A., author
Vasquez, Bernard J., author
Schwadron, Nathan A., author
Cannon, Bradford E., author
Richardson, John D., author
Type of Resource: text
Genre: Text
Date Issued: 2016-05-10
Physical Form: computer
online resource
Extent: 1 online resource
Language(s): English
Abstract/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.
Identifier: FSU_libsubv1_wos_000377204900037 (IID), 10.3847/0004-637X/822/2/94 (DOI)
Keywords: dissipation range, ibex ribbon, instabilities, jupiters distant magnetotail, low-frequency turbulence, magnetic fields, magnetohydrodynamic turbulence, mhd turbulence, rotating rarefaction regions, solar wind, solar-wind turbulence, statistical-analysis, Sun: heliosphere, turbulence, ulysses observations, waves
Publication Note: The publisher’s version of record is available at http://www.dx.doi.org/10.3847/0004-637X/822/2/94
Persistent Link to This Record: http://purl.flvc.org/fsu/fd/FSU_libsubv1_wos_000377204900037
Host Institution: FSU
Is Part Of: Astrophysical Journal.
0004-637X
Issue: iss. 2, vol. 822

Choose the citation style.
Aggarwal, P., Taylor, D. K., Smith, C. W., Joyce, C. J., Fisher, M. K., Isenberg, P. A., … Richardson, J. D. (2016). VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2-6 au. Astrophysical Journal. Retrieved from http://purl.flvc.org/fsu/fd/FSU_libsubv1_wos_000377204900037