The source of the very energetic (GeV range) galactic cosmic rays (GCR) is not known. Occasionally (one event per square kilometer per century) one measures energies as high as 10^20 eV (Schwarzschild, 1997), and no one knows yet how this can be achieved. One possibility is that shock waves from expanding supernovas are doing the trick.
GCR are the most typical cosmic rays, and their flux in the solar system is modulated by the solar activity: enhanced solar wind shields the system from these particles (Forbush, 1954; for more about the history, see Simpson, 1994). The effect is clearly seen from the cosmic ray measurements covering several solar cycles (see also space climate). Quite interesting fact is that also the 22-year modulation is seen in the recovery of GCR intensities: during even cycles it is completed much faster than during odd cycles (Ahluwalia, 1979, 1980).
GCR form also one of the radiation belts.
- Ahluwalia, H. S., Eleven year variation of cosmic ray intensity and solar polar field reversals, Conf. Pap. Int. Cosmic Ray Conf. 16th, 12, 182-189, 1979.
- Ahluwalia, H. S., Solar polar field reversals and secular variations of cosmic ray intensity, in Solar and Interplanetary Dynamics, edited by M. Dryer and E. Tanderg-Hanssen, D. Reidel, pp. 79-89, Norwell, Mass., 1980.
- Forbush, S. E., Worldwide cosmic ray variations, 1937-1952, J. Geophys. Res., 59, 525-542, 1954.
- Schwarzschild, B., Auger project seeks to study highest energy cosmic rays, Physics Today, February 1997, pp. 19-21, 1997.
- Simpson, J. A., A physicist in the world of geophysics and space, J. Geophys. Res., 99, 19159-19173, 1994.