Solar Physics

, Volume 289, Issue 1, pp 391–406 | Cite as

Modulation of Galactic Protons in the Heliosphere During the Unusual Solar Minimum of 2006 to 2009

  • M. S. PotgieterEmail author
  • E. E. Vos
  • M. Boezio
  • N. De Simone
  • V. Di Felice
  • V. Formato


The last solar minimum activity period, and the consequent minimum modulation conditions for cosmic rays, was unusual. The highest levels of galactic protons were recorded at Earth in late 2009 in contrast to expectations. Proton spectra observed for 2006 to 2009 from the PAMELA cosmic ray detector on-board the Resurs-DK1 satellite are presented together with the solutions of a comprehensive numerical model for the solar modulation of cosmic rays. The model is used to determine what mechanisms were mainly responsible for the modulation of protons during this period, and why the observed spectrum for 2009 was the highest ever recorded. From mid-2006 until December 2009 we find that the spectra became significantly softer because increasingly more low energy protons had reached Earth. To simulate this effect, the rigidity dependence of the diffusion coefficients had to decrease significantly below ∼ 3 GeV. The modulation minimum period of 2009 can thus be described as relatively more ‘diffusion dominated’ than previous solar minima. However, we illustrate that drifts still had played a significant role but that the observable modulation effects were not as well correlated with the waviness of the heliospheric current sheet as before. Protons still experienced global gradient and curvature drifts as the heliospheric magnetic field had decreased significantly until the end of 2009, in contrast to the moderate decreases observed during previous minimum periods. We conclude that all modulation processes contributed to the observed increases in the proton spectra for this period, exhibiting an intriguing interplay of these major mechanisms.


Cosmic rays Solar modulation Solar minimum activity Galactic protons 



The South African authors express their gratitude for the partial funding granted by the South African National Research Foundation (NRF) under the Italy–South Africa Research Cooperation Programme. They also thank the INFN for the partial financial support when visiting in Trieste and Rome over a span of three years.


  1. Adriani, O., Barbarino, G.C., Bazilevskaya, G.A., Bellotti, R., Boezio, M., Bogomolov, E.A., et al.: 2009a, Phys. Rev. Lett. 102, 051101. ADSCrossRefGoogle Scholar
  2. Adriani, O., Barbarino, G.C., Bazilevskaya, G.A., Bellotti, R., Boezio, M., Bogomolov, E.A., et al.: 2009b, Nature 458, 607. ADSCrossRefGoogle Scholar
  3. Adriani, O., Barbarino, G.C., Bazilevskaya, G.A., Bellotti, R., Boezio, M., Bogomolov, E.A., et al.: 2011, Science 332, 69. ADSCrossRefGoogle Scholar
  4. Adriani, O., Barbarino, G.C., Bazilevskaya, G.A., Bellotti, R., Boezio, M., Bogomolov, E.A., et al.: 2013, Astrophys. J. 765, 91. ADSCrossRefGoogle Scholar
  5. Ahluwalia, H.S., Ygbuhay, R.C.: 2011, Adv. Space Res. 48, 61. ADSCrossRefGoogle Scholar
  6. Aslam, O.P.M., Badruddin: 2012, Solar Phys. 279, 269. ADSCrossRefGoogle Scholar
  7. Boezio, M., Pearce, M., Picozza, P., Sparvoli, R., Spillantini, P., Adriani, O., et al.: 2009, New J. Phys. 11, 105023. ADSCrossRefGoogle Scholar
  8. Burlaga, L.F., Goldstein, M.L., McDonald, F.B., Lazarus, A.J.: 1985, J. Geophys. Res. 90, 12027. ADSCrossRefGoogle Scholar
  9. Cliver, E.W., Richardson, I.G., Ling, A.G.: 2011, Space Sci. Rev. doi: 10.1007/s11214-011-9746-3. Google Scholar
  10. De Simone, N., Di Felice, V., Gieseler, J., Boezio, M., Casolino, M., Picozza, P., et al.: 2011, Astrophys. Space Sci. Trans. 7, 425. ADSCrossRefGoogle Scholar
  11. Ferreira, S.E.S., Potgieter, M.S.: 2002, J. Geophys. Res. 107, SHPX:1-10. CrossRefGoogle Scholar
  12. Ferreira, S.E.S., Potgieter, M.S., Burger, R.A., Heber, B., Fichtner, H.: 2001, J. Geophys. Res. 106, 24979. ADSCrossRefGoogle Scholar
  13. Ferreira, S.E.S., Potgieter, M.S., Moeketsi, D.M., Heber, B., Fichtner, H.: 2003, Astrophys. J. 594, 552. ADSCrossRefGoogle Scholar
  14. Heber, B., Potgieter, M.S.: 2006, Space Sci. Rev. 127, 117. ADSCrossRefGoogle Scholar
  15. Heber, B., Potgieter, M.S.: 2008, In: Balogh, A., Lanzerotti, L.J., Suess, T. (eds.) The Heliosphere Through the Solar Activity Cycle, Praxis, Chichester. Google Scholar
  16. Heber, B., Kopp, A., Gieseler, J., Müller-Mellin, R., Fichtner, H., Scherer, K., et al.: 2009, Astrophys. J. 699, 1956. ADSCrossRefGoogle Scholar
  17. Hoeksema, J.T.: 1991, In: Marsch, E., Schwenn, R. (eds.) Solar Wind Seven Colloquium, 191. Google Scholar
  18. Jokipii, J.R., Kopriva, D.A.: 1979, Astrophys. J. 234, 384. ADSCrossRefGoogle Scholar
  19. Kane, R.P.: 2011, Solar Phys. 269, 451. ADSCrossRefGoogle Scholar
  20. Langner, U.W., Potgieter, M.S.: 2004, J. Geophys. Res. 109, 1. CrossRefGoogle Scholar
  21. Langner, U.W., Potgieter, M.S., Webber, W.R.: 2004, Adv. Space Res. 34, 138. ADSCrossRefGoogle Scholar
  22. Langner, U.W., Potgieter, M.S., Fichtner, H., Borrmann, T.: 2006, Astrophys. J. 640, 1119. ADSCrossRefGoogle Scholar
  23. McDonald, F.B., Webber, W.R., Reames, D.V.: 2010, Geophys. Res. Lett. 37, L18101:1-5. CrossRefGoogle Scholar
  24. Mewaldt, R.A., Davis, A.J., Lave, K.A., Leske, R.A., Stone, E.C., Wiedenbeck, M.E., et al.: 2010, Astrophys. J. Lett. 273, L1. ADSCrossRefGoogle Scholar
  25. Mewaldt, R.A.: 2012, Space Sci. Rev. doi: 10.1007/s11214-012-9922-0. Google Scholar
  26. Moeketsi, D.M., Potgieter, M.S., Ferreira, S.E.S., Heber, B., Fichtner, H., Henize, V.K.: 2005, Adv. Space Res. 35, 597. ADSCrossRefGoogle Scholar
  27. Ngobeni, M.D., Potgieter, M.S.: 2008, Adv. Space Res. 41, 373. ADSCrossRefGoogle Scholar
  28. Ngobeni, M.D., Potgieter, M.S.: 2010, Adv. Space Res. 46, 391. ADSCrossRefGoogle Scholar
  29. Ngobeni, M.D., Potgieter, M.S.: 2011, Adv. Space Res. 48, 300. ADSCrossRefGoogle Scholar
  30. Nkosi, S., Potgieter, M.S., Ferreira, S.E.S.: 2008, Planet. Space Sci. 56, 501. ADSCrossRefGoogle Scholar
  31. Nkosi, G.S., Potgieter, M.S., Webber, W.R.: 2011, Adv. Space Res. 48, 1480. ADSCrossRefGoogle Scholar
  32. Parker, E.N.: 1965, Planet. Space Sci. 13, 9. ADSCrossRefGoogle Scholar
  33. Potgieter, M.S.: 2000, J. Geophys. Res. 105, 18295. ADSCrossRefGoogle Scholar
  34. Potgieter, M.S.: 2011, Space Sci. Rev. doi: 10.1007/s11214-011-9750-7. zbMATHGoogle Scholar
  35. Potgieter, M.S., Ferreira, S.E.S.: 2001, Adv. Space Res. 27, 481. ADSCrossRefGoogle Scholar
  36. Potgieter, M.S., le Roux, J.A., Burger, R.A.: 1989, J. Geophys. Res. 94, 2323. ADSCrossRefGoogle Scholar
  37. Potgieter, M.S., le Roux, J.A.: 1992, Astrophys. J. 386, 336. ADSCrossRefGoogle Scholar
  38. Potgieter, M.S., Moraal, H.: 1985, Astrophys. J. 294, 425. ADSCrossRefGoogle Scholar
  39. Reinecke, J.P.L., Potgieter, M.S.: 1994, J. Geophys. Res. 99, 14761. ADSCrossRefGoogle Scholar
  40. Scherer, K., Fichtner, H., Strauss, R.D., Ferreira, S.E.S., Potgieter, M.S., Fahr, H.-J.: 2011, Astrophys. J. 735, 128. ADSCrossRefGoogle Scholar
  41. Strauss, R.D., Potgieter, M.S., Ferreira, S.E.S.: 2011, Adv. Space Res. 48, 65. ADSCrossRefGoogle Scholar
  42. Strauss, R.D., Potgieter, M.S., Kopp, A., Büsching, I.: 2011, J. Geophys. Res. 116, A12105. ADSCrossRefGoogle Scholar
  43. Shalchi, A.: 2009, Astrophys. Space Sci. Lib. 362, Springer, Berlin. Google Scholar
  44. Teufel, A., Schlickeiser, R.: 2002, Astron. Astrophys. 393, 703. ADSCrossRefGoogle Scholar
  45. Webber, W.R., Potgieter, M.S., Burger, R.A.: 1990, Astrophys. J. 349, 634. ADSCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • M. S. Potgieter
    • 1
    Email author
  • E. E. Vos
    • 1
  • M. Boezio
    • 2
  • N. De Simone
    • 3
  • V. Di Felice
    • 3
  • V. Formato
    • 2
  1. 1.Centre for Space ResearchNorth-West UniversityPotchefstroomSouth Africa
  2. 2.INFNSezione di TriesteTriesteItaly
  3. 3.INFNSezione di Roma Tor VergataRomeItaly

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