Astrophysics and Space Science

, Volume 20, Issue 2, pp 267–285 | Cite as

The propagation of Alfvén waves and their directional anisotropy in the solar wind

  • Heinrich J. Völk
  • Werner Aplers
Article

Abstract

The propagation of solar Alfvén waves in interplanetary space is studied in the approximation of geometrical optics. Ray paths and the change of wave vectors and amplitudes along the rays are determined assuming an Archimedean-spiral interplanetary magnetic field. In particular, the Alfvénic fluctuations in the 2 directions perpendicular to the magnetic field direction are calculated under the assumption that the Alfvén waves are produced at the Sun and emitted with an isotropic directional distribution from a reference level close to the Sun. It turns out that due to the combined effect of spherical expansion of the solar wind flow and the spiralling of the interplanetary field the magnetic fluctuations in the direction perpendicular both to the unperturbed field and the radial direction have much more power than in the other directions (directional anisotropy).

Our results are compared with spacecraft observations made by Belcher and Davis (1971), that show an anisotropy of a similar character. It is argued that under average conditions the physical process leading to an anisotropy is not selective coupling of Alfvén waves into compressional waves, as suggested by Belcher and Davis, but rather the above mentioned dissipationfree effect of geometrical optics. Finally, arguments are presented to explain the discrepancy between the calculated high anisotropy and the measured low anisotropy in terms of finite amplitude effects and wavescattering.

Keywords

Anisotropy Solar Wind Compressional Wave Interplanetary Magnetic Field Geometrical Optic 

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References

  1. Barnes, A.: 1969,Astrophys. J. 155, 311.Google Scholar
  2. Barnes, A. and Suffolk, G. C. J.: 1971,J. Plasma Phys. 5, 315.Google Scholar
  3. Bazer, J. and Hurley, J.: 1963,J. Geophys. Res. 68, 147.Google Scholar
  4. Belcher, J. and Davis, L., Jr.: 1971,J. Geophys. Res. 76, 3534.Google Scholar
  5. Belcher, J. W., Davis, L., Jr. and Smith, E. J.: 1969,J. Geophys. Res. 74, 2302.Google Scholar
  6. Boillat, G.: 1970,J. Math. Phys. 11, 941.Google Scholar
  7. Burlaga, L. F.: 1968,Solar Phys. 4, 67.Google Scholar
  8. Burlaga, L. F.: 1969,Solar Phys. 7, 54.Google Scholar
  9. Burlaga, L. F.: 1971a,J. Geophys. Res. 76, 4360.Google Scholar
  10. Burlaga, L. F.: 1971b, ‘The Solar Envelope’, Goddard Space Flight Center, Report X-692-71-400.Google Scholar
  11. Coleman, P. J., Jr.: 1967,Planetary Space Sci. 15, 953.Google Scholar
  12. Coleman, P. J., Jr.: 1968,Astrophys. J. 153, 371.Google Scholar
  13. Frisch, V.: 1964,Ann. Astrophys. 27, 224.Google Scholar
  14. Galeev, A. A. and Orajewsky, V. N.: 1963,Sov. Phys.-Dokl. 7, 988.Google Scholar
  15. Hollweg, J. V.: 1971a,J. Geophys. Res.,76, 5155.Google Scholar
  16. Hollweg, J. V.: 1971b,Phys. Rev. Letters Nov. 1971.Google Scholar
  17. Jeffrey, A. and Taniuti, T.: 1964,Nonlinear Wave Propagation, Academic Press, New York, London, p. 194.Google Scholar
  18. Kadomtsev, B. B.: 1965Plasma Turbulence, Academic Press, London.Google Scholar
  19. Kantrowitz, A. R. and Petschek, H. E.: 1966, in W. B. Kunkel (ed.),Plasma Physics in Theory and Application, pp. 148–206, McGraw Hill, New York.Google Scholar
  20. Lüst, R.: 1959,über die Ausbreitung von Wellen in einem Plasma, Fortschritte der Physik, Vol. VII, 503.Google Scholar
  21. Montgomery, D.: 1959,Phys. Rev. Letters 2, 36.Google Scholar
  22. Ness, N. F.: 1969,Proc. 13th. Int. Conf. on Cosmic Rays, Budapest, Hungary, in press.Google Scholar
  23. Osterbrok, D. E.: 1961,Astrophys. J. 134, 347.Google Scholar
  24. Parker, E. N.: 1963,Interplanetary Dynamical Processes, John Wiley, New York.Google Scholar
  25. Parker, E. N.: 1965,Space Sci. Rev. 4, 66.Google Scholar
  26. Sari J. W. and Ness, N. F.: 1969,Solar Phys. 8, 155.Google Scholar
  27. Schatten, K. H., Ness, N. F. and Wilcox, J. M.: 1969,Solar Phys. 9, 442.Google Scholar
  28. Unti, T. W. J. and Neugebauer, M.: 1968,Phys. Fluids 11, 563.Google Scholar
  29. Valley, G. C.: 1971,Astrophys. J. 168, 251.Google Scholar
  30. Völk, H. J. and Aplers, W.: 1972, in K. Schindler (ed.),Cosmic Plasma Physics, Plenum Press, New York, London, pp. 105–111.Google Scholar

Copyright information

© D. Reidel Publishing Company 1973

Authors and Affiliations

  • Heinrich J. Völk
    • 1
  • Werner Aplers
    • 1
  1. 1.Institut für extraterrestrische PhysikMax-Planck-Institut für Physik und AstrophysikGarching bei MunchenFRG

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