Solar Physics

, Volume 289, Issue 7, pp 2653–2668 | Cite as

Galactic Cosmic Ray Modulation near the Heliospheric Current Sheet

  • S. R. Thomas
  • M. J. Owens
  • M. Lockwood
  • C. J. Scott


Galactic cosmic rays (GCRs) are modulated by the heliospheric magnetic field (HMF) both over decadal time scales (due to long-term, global HMF variations), and over time scales of a few hours (associated with solar wind structures such as coronal mass ejections or the heliospheric current sheet, HCS). Due to the close association between the HCS, the streamer belt, and the band of slow solar wind, HCS crossings are often associated with corotating interaction regions where fast solar wind catches up and compresses slow solar wind ahead of it. However, not all HCS crossings are associated with strong compressions. In this study we categorize HCS crossings in two ways: Firstly, using the change in magnetic polarity, as either away-to-toward (AT) or toward-to-away (TA) magnetic field directions relative to the Sun and, secondly, using the strength of the associated solar wind compression, determined from the observed plasma density enhancement. For each category, we use superposed epoch analyses to show differences in both solar wind parameters and GCR flux inferred from neutron monitors. For strong-compression HCS crossings, we observe a peak in neutron counts preceding the HCS crossing, followed by a large drop after the crossing, attributable to the so-called ‘snow-plough’ effect. For weak-compression HCS crossings, where magnetic field polarity effects are more readily observable, we instead observe that the neutron counts have a tendency to peak in the away magnetic field sector. By splitting the data by the dominant polarity at each solar polar region, we find that the increase in GCR flux prior to the HCS crossing is primarily from strong compressions in cycles with negative north polar fields due to GCR drift effects. Finally, we report on unexpected differences in GCR behavior between TA weak compressions during opposing polarity cycles.


Cosmic rays Heliospheric current sheet 22-year cycle Energetic particles 



We are grateful to the Space Physics Data Facility (SPDF) of NASA’s Goddard Space Flight Centre for combining the data into the OMNI 2 dataset which was obtained via the GSFC/SPDF OMNIWeb interface at . We also thank the Bartol Research Institute of the University of Delaware for the neutron monitor data from McMurdo, which is supported by NSF grant ATM-0527878. The work of SRT is supported by a studentship from the UK’s Natural Environment Research Council (NERC).


  1. Ahluwalia, H.S.: 1994, Cosmic ray transverse gradient for a Hale Cycle. J. Geophys. Res. 99, 23515 – 23521. ADSCrossRefGoogle Scholar
  2. Aslam, O.P.M., Badruddin: 2012, Solar modulation of cosmic rays during the declining and minimum phases of solar cycle 23: Comparison with past three solar cycles. Solar Phys. 279, 269 – 288. ADSCrossRefGoogle Scholar
  3. Badruddin, Ananth, A.G.: 2003, Variation of cosmic ray intensity with angular distance from Earth to the current sheet. In: 28th Int. Cosmic Ray Conf., 3909 – 3912. Google Scholar
  4. Badruddin, Yadav, R.S., Yadav, N.R.: 1985, Intensity variation of cosmic rays near the heliospheric current sheet. Planet. Space Sci. 2, 191 – 201. ADSGoogle Scholar
  5. Barnard, L., Lockwood, M.: 2011, A survey of gradual solar energetic particle events. J. Geophys. Res. 116, A05103. ADSGoogle Scholar
  6. Bieber, J.W., Clem, J.M., Duldig, M.L., Evenson, P.A., Humble, J.E., Pyle, R.: 2004, Latitudinal survey observations of neutron monitor multiplicity. J. Geophys. Res. 109, A12106. ADSCrossRefGoogle Scholar
  7. Borovsky, J.E., Denton, M.H.: 2010, Solar wind turbulence and shear: a superposed-epoch analysis of corotating interaction regions at 1AU. J. Geophys. Res. 115, A12228. CrossRefGoogle Scholar
  8. Crooker, N.U., McPherron, R.L.: 2012, Coincidence of composition and speed boundaries of the slow solar wind. J. Geophys. Res. 117, A09104. ADSGoogle Scholar
  9. Crooker, N.U., McAllister, A.H., Fitzenreiter, R.J., Linker, J.A., Larson, D.E., Lepping, R.P., Szabo, A., Steinberg, J.T., Lazarus, A.J., Mikic, Z., Lin, R.P.: 1998, Sector boundary transformation by an open magnetic cloud. J. Geophys. Res. 103, 26859 – 26868. ADSCrossRefGoogle Scholar
  10. El Borie, M.A.: 2001, Cosmic ray intensities near the heliospheric current sheet throughout three solar activity cycles. J. Phys. G 27, 773 – 785. ADSCrossRefGoogle Scholar
  11. El Borie, M.A., Duldig, M.L., Humble, J.E.: 1998, Galactic cosmic ray modulation and the passage of the heliospheric current sheet at Earth. Planet. Space Sci. 46, 439 – 448. ADSCrossRefGoogle Scholar
  12. Hale, G.E., Nicholson, S.B.: 1925, The law of Sun-spot polarity. Astrophys. J. 62, 270 – 300. ADSCrossRefGoogle Scholar
  13. Hoeksema, J.T., Wilcox, J.M., Scherrer, P.H.: 1983, The structure of the heliospheric current sheet – 1978 – 1982. J. Geophys. Res. 88, 9910 – 9918. ADSCrossRefGoogle Scholar
  14. Jokipii, J.R., Levy, E.H., Hubbard, W.B.: 1977, Effects of particle drift on cosmic ray transport. I. General properties, application to solar modulation. Astrophys. J. 213, 861 – 868. ADSCrossRefGoogle Scholar
  15. King, J.H., Papitashvili, N.E.: 2005, Solar wind spatial scales in and comparisons of hourly wind and ACE plasma and magnetic field data. J. Geophys. Res. 110, A02104. ADSGoogle Scholar
  16. Kruger, H., Moraal, H., Bieber, J.W., Clem, J.M., Evenson, P.A., Pyle, K.R., Duldig, M.L., Humble, J.E.: 2008, A calibration neutron monitor: energy response and instrumental temperature sensitivity. J. Geophys. Res. 113, A08101. ADSGoogle Scholar
  17. Krymsky, G.F., Krivoshapkin, P.A., Gerasimova, S.K., Gololobov, P.Y., Grogor’ev, V.G., Starodubtsev, S.A.: 2012, Heliospheric modulation of cosmic rays in solar cycles 19 – 23. Astron. Lett. 9, 609 – 612. ADSCrossRefGoogle Scholar
  18. Lockwood, M., Owens, M.J., Barnard, L., Davis, C.J., Thomas, S.R.: 2012, What is the Sun up to? Astron. Geophys. 53, 3.9 – 3.15. Google Scholar
  19. Mavromichalaki, H., Paouris, E.: 2012, Long term cosmic ray variability and the CME-index. Adv. Astron. 607172. Google Scholar
  20. McComas, D.J., Dayeh, M.A., Allegrini, F., Bzowski, M., de Majistre, R., Fujiki, K., Funsten, H.O., Fuselier, S.A., Gruntman, M., Janzen, P.H., Kubiak, M.A., Kucharek, H., Livadiotis, G., Moebius, E., Reisenfeld, D.B., Reno, M., Schwadron, N.A., Sokol, J.M., Tokumaru, M.: 2012, The first three years of IBEX observations and our evolving heliosphere. Astrophys. J. Suppl. 203, 1. ADSCrossRefGoogle Scholar
  21. McCracken, K.G., Ness, N.F.: 1966, The collimation of cosmic rays by the interplanetary magnetic field. J. Geophys. Res. 71, 3315 – 3318. ADSCrossRefGoogle Scholar
  22. McCracken, K.G., McDonald, F.B., Beer, J., Raisbeck, G., Yiou, F.: 2004, A phenomenological study of the long-term cosmic ray modulation, 850 – 1958 AD. J. Geophys. Res. 109, A12103. ADSCrossRefGoogle Scholar
  23. Owens, M.J., Usoskin, I., Lockwood, M.: 2012, Heliospheric modulation of galactic cosmic rays during Grand Solar Maxima: Past and future variations. Geophys. Res. Lett. 39, 19102. ADSCrossRefGoogle Scholar
  24. Owens, M.J., Lockwood, M., Barnard, L., Davis, C.J.: 2011, Solar cycle 24: Implications for energetic particles and long-term space climate change. Geophys. Res. Lett. 38, L19106. ADSCrossRefGoogle Scholar
  25. Paouris, E., Mavromichalaki, H., Belov, A., Guischina, R., Yanke, V.: 2012, Galactic cosmic ray modulation and the last solar minimum. Solar Phys. 280, 255 – 271. ADSCrossRefGoogle Scholar
  26. Parker, E.N.: 1965, The passage of energetically charged particles through interplanetary space. Planet. Space Sci. 13, 9 – 49. ADSCrossRefGoogle Scholar
  27. Richardson, I.G.: 2004, Energetic particles and corotating interaction regions in the solar wind. Space Sci. Rev. 111, 267 – 376. ADSCrossRefGoogle Scholar
  28. Richardson, I.G., Cane, H.V., Wibberenz, G.: 1999, A 22-year dependence in the size of near-ecliptic corotating cosmic ray depressions during five solar minima. J. Geophys. Res. 104, 12549 – 12562. ADSCrossRefGoogle Scholar
  29. Rouillard, A., Lockwood, M.: 2007, The latitudinal effect of corotating interaction regions on galactic cosmic rays. Solar Phys. 245, 191 – 206. ADSCrossRefGoogle Scholar
  30. Scott, C.J., Harrison, R.G., Owens, M.J., Lockwood, M., Barnard, L.: 2013, Solar wind modulation of UK lightning. Environ. Res. Lett., in press. Google Scholar
  31. Smith, E.N.: 2001, The heliospheric current sheet. J. Geophys. Res. 106, 15819 – 15831. ADSCrossRefGoogle Scholar
  32. Steinhilber, F., Beer, J., Frohlich, C.: 2009, Total solar irradiance during the past 9300 years inferred from the cosmogenic radionuclide Beryllium-10. AGU, Fall Meeting, GC24A-03, in press. Google Scholar
  33. Steinhilber, F., Abreu, J., Beer, J., McCracken, K.: 2010, Interplanetary magnetic field during the past 9300 years inferred from cosmogenic radionuclides. J. Geophys. Res. 115, A01104. ADSGoogle Scholar
  34. Thomas, B.T., Smith, E.J.: 1981, The structure and dynamics of the heliospheric current sheet. J. Geophys. Res. 86, 11105 – 11110. ADSCrossRefGoogle Scholar
  35. Thomas, S.R., Owens, M.J., Lockwood, M.: 2013, The 22-year Hale Cycle in cosmic ray flux – Evidence for direct heliospheric modulation. Solar Phys. 289, 407 – 421. ADSCrossRefGoogle Scholar
  36. Tritakis, V.P.: 1984, Heliospheric current sheet displacements during the Solar Cycle evolution. J. Geophys. Res. 89, 6588 – 6598. ADSCrossRefGoogle Scholar
  37. Tsurutani, B.T., Gonzales, W.D., Gonzales, A.L.C., Tang, F., Arballo, J.K., Okada, M.: 1995, Interplanetary origin of geomagnetic activity in the declining phase of the solar cycle. J. Geophys. Res. 100, 21717 – 21734. ADSCrossRefGoogle Scholar
  38. Usoskin, I.G., Bazilevskaya, G.A., Kovaltsov, G.A.: 2011, Solar modulation parameter for cosmic rays since 1936 reconstructed from ground-based neutron monitors and ionization chambers. J. Geophys. Res. 116, A02104. ADSGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2014

Authors and Affiliations

  • S. R. Thomas
    • 1
  • M. J. Owens
    • 1
  • M. Lockwood
    • 1
  • C. J. Scott
    • 1
  1. 1.University of ReadingReadingUK

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