Advertisement

Auroral Electron Beams near the Magnetic Equator

  • Carl E. McIlwain

Abstract

Intense beams of electrons travelling parallel to the local magnetic field have been observed at a magnetic latitude of 11° and a radial distance of 6.6 Re. The distribution function for electrons travelling within 8° of the field line direction is typically flat or slightly rising up to a break point beyond which it decreases as v−5 to v−10. The energy corresponding to the break point velocity is usually between 0.1 and 10 keV. These beams are found to occur on closed field lines at the inner edge of the plasma sheet and thus at the root of the earth’s magnetotail. Beams with break point energies greater than 2 k seem to occur only within the first 10 minutes after the onset of hot plasma injection associated with a magnetospheric substorm. Although the origin and destiny of these electrons is as yet unknown, considerations of the total energy and the number of particles transported guarantee that they must play a dominant role in many key magnetospheric processes.

Keywords

Pitch Angle Plasma Sheet Magnetic Field Direction Magnetic Equator Parallel Electric Field 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Albert, R. D., Nearly monoenergetic electron fluxes detected during a visible aurora, phys. Rev, Letters, 18, 369, 1967a.ADSCrossRefGoogle Scholar
  2. Armstrong, J. C., Field aligned currents in the magnetosphere, Magnetospheric physics, ed. B. M. Mormac, p. 155, D. Reidel Pub. Co.., Dordrecht, Holland, 1974. (Ref. in Ztnuda, A. J., and J. C. Armstrong, The diurnal flow pattern of field-aligned currents, J. Geophys. Res. 79, 4611, 1974).Google Scholar
  3. Arnoldy, R, L., Auroral particle precipitation and Birkeland currents, Rev, of Geophys. and Space phys, 12, 217, 1974.ADSCrossRefGoogle Scholar
  4. Arnoldy, R. L., R. B. Lewis, and P. O. Isaacson, Field-aligned auroral electron fluxes, J. Geophys. Res., 79, 4208, 1974.ADSCrossRefGoogle Scholar
  5. Axford, W. I., Magnetospheric convection, Rev, of Geophys, 7, 421, 1969.ADSCrossRefGoogle Scholar
  6. Boström, R., Ionosphere-magnetosphere coupling, Magnetospheric Physics, ed. B. M. Mormac, p. 45, D. Reidel Pub. Co., Dordrecht, Holland, 1974.Google Scholar
  7. Bryant, D. A., G. M. Courtier, and G. Bennett, Electron Intensities over auroral arcs, Earth’s Magnetospheric processes, ed, B. M. Mormac, p. 141, D. Reidel pub. Co., Dordrecht, Holland, 1972.Google Scholar
  8. Choy, L. W., R. L. Arnoldy, W. Potter, p. Kintner, and L. J. Cahill, Field-Aligned particle currents near an auroral arc, J. Geophys. Res, 75, 8279, 1971. (Ref. in Zmuda and Armstrong, The diurnal flow pattern of field aligned currents, J. Geophys. Res. 79, 4611,1974.)ADSCrossRefGoogle Scholar
  9. Cloutier, p. A., B. R. Sandel, H. R. Anderson, P. M. pazich, and R. J. Spiger, Measurement of auroral Birkeland currents and energetic particle fluxes, J. Geophys. Res, 78, 640, 1973.ADSCrossRefGoogle Scholar
  10. DeForest, S. E., and C. E. Mcllwain, Plasma clouds in the magnetosphere, J. Geophys. Res. 76, 3587, 1971.ADSCrossRefGoogle Scholar
  11. Evans, D. S., Fine structure in the energy spectrum of low energy auroral electrons, in Atmospheric Emissions, eds. B. M. Mormac and A. Omholt, p. 107, Van Nostrand Reinhold, New York, 1969.Google Scholar
  12. Evans, D. S., Observations of a near monoenergetic flux of auroral electrons, J. Geophys. Res, 73, 2315, 1968.ADSCrossRefGoogle Scholar
  13. Evans, D. S., Precipitating electron fluxes formed by a magnetic field aligned potential difference, J. Geophys. Res. 79, 2853, 1975.ADSCrossRefGoogle Scholar
  14. Fälthammar, C.-G., Magnetospheric processes, Earth’s Magnetospheric processes, ed. B. M. Mormac, p. 16–28, D. Reidel pub. Co., Dordrecht, Holland, 1972.Google Scholar
  15. Hall, D. S., and D. A. Bryant, Collimation of auroral particles by time-varying acceleration, Nature 251, 5474, 1974.CrossRefGoogle Scholar
  16. Heikkila, W. J., Outline of a magnetospheric theory, J. Geophys. Res. 79, 2496, 1974.ADSCrossRefGoogle Scholar
  17. Hones, E. W., Jr., J. R. Asbridge, S. J. Bame, and S. Singer, Energy spectra and angular distributions of particles in the plasma sheet and their comparison with rocket measurements over the auroral zone, J. Geophys. Res. 76, 63, 1971.ADSCrossRefGoogle Scholar
  18. Hultqvist, B., On the production of a magnetic-field-aligned electric field by the interaction between the hot magnetospheric plasma and the cold ionosphere, Planet. Space Sei. 19, 749, 1971.ADSCrossRefGoogle Scholar
  19. Hultqvist, B., H. Borg, W. Riedler, and p. Christophersen, Observations of magnetic-field aligned anisotropy for 1 and 6 k positive ions in the upper ionosphere, planet. Space Sci. 19, 279, 1971.ADSCrossRefGoogle Scholar
  20. Kamide, Y., and C.E. Mcllwain, The onset time of magnetospheric substorms determined from ground and synchronous satellite records, J. Geophys. Res. 79, 4787, 1974.ADSCrossRefGoogle Scholar
  21. Lenard, -, Über die Absorption der Nordlichtstrahlen in der Erdatmosphäre1, S. B. Heidelberg. Adal. Wiss., Math. Naturw. Kl. 1911, No. 12.(Ref. in International Monographs on Radio, ed. by E. Appleton and R. L. Smith-Rose, Oxford University press, London, p. 192, 1955.)Google Scholar
  22. Mauk, B. H., and C. E. Mcllwain, Correlation of K with the substorm-injected plasma boundary, J. Geophys. Res. 79, 3193,1974.ADSCrossRefGoogle Scholar
  23. Mcllwain, C. E., Direct measurement of particles producing visible auroras, J. Geophys. Res. 65, 2727, 1960.ADSCrossRefGoogle Scholar
  24. Mcllwain, C. E., Plasma convection in the vicinity of the geosynchronous orbit, Earth’s Magnetospheric Processes, ed. B. M. Mormac, p. 268, D. Reidel pub. Co., Dordrecht, Holland, 1972.Google Scholar
  25. Mcllwain, C. E., Substorm injection boundaries, Magnetospheric Physics, ed. B. M. Mormac, D. Reidel Pub. Co., Dordrecht, Holland, 1974.Google Scholar
  26. O’Brien, B., and D. L. Reasoner, Measurements of highly collimated, short-duration bursts of auroral electrons and comparison with existing auroral models, J. Geophys. Res. 76, 8258, 1971.ADSCrossRefGoogle Scholar
  27. Omholt, A., Studies on the excitation of aurora borealis, 1, the hydrogen lines, Geofys. Publikasjoner, 20 (11), 1–40,1959.Google Scholar
  28. Schulz, M., particle lifetimes in strong diffusion, Astrophys. & Space Science 31, 37, 1974.ADSCrossRefGoogle Scholar
  29. Shook, G. B., R. D. Sharp, M. F. Shea, R. G. Johnson, and J. B. Reagan, Trans. Am. Geophys. U. 47, 64, 1966.Google Scholar
  30. Störmer, C., The polar aurora, Oxford University press, London, 1955.zbMATHGoogle Scholar
  31. Vondrak, R. R., H. R. Anderson, and R. J. Spiger, Rocket-based measurements of particle fluxes and currents in an auroral arc, J. Geophys. Res. 76, 7701, 1971. (Ref. in Zmuda and Armstrong, The diurnal flow pattern of aligned currents, J. Geophys. Res. 79, 4911, 1974).ADSCrossRefGoogle Scholar
  32. Westerlund, L. H., The auroral energy spectra extended to 45, J. Geophys. Res., 74, 351, 1969.ADSCrossRefGoogle Scholar
  33. Whalen, B. A., and I. B. Miarmid, Observations of magneticfield-aligned auroral electron precipitation, J. Geophys.Res. 77, 191, 1972.ADSCrossRefGoogle Scholar
  34. Whipple, E. C., private communication, 1975.Google Scholar
  35. Zmuda, A. J., and J. C. Armstrong, The diurnal flow pattern of field-aligned currents, J. Geophys. Res. 79, 4611, 1947.ADSCrossRefGoogle Scholar

Copyright information

© Plenum Press, New York 1975

Authors and Affiliations

  • Carl E. McIlwain
    • 1
  1. 1.Physics Dept.University of CaliforniaSan Diego, La JollaUSA

Personalised recommendations