Features of the time behavior of the amplitude of 27-day variations in galactic cosmic rays

Variations in various parameters of the interplanetary and circumterrestrial space with a solar-rotation period of 27 days are analyzed over a time interval covering solar-activity cycles 21 and 22. The parameters analyzed include the galactic cosmic-ray intensity (neutron monitor data), the magnetic field of the Sun as a star (Stanford data), solar-wind velocity, magnitude of the interplanetary magnetic field (IMF), and geomagnetic activity index K-p. The solar-activity cycle is shown to have certain critical points when the amplitudes of the 27-day variations undergo abrupt changes.