The 24 hour intensity variations of the primary cosmic rays

Abstract

The data from nucleonio component detectors (neutron intensity monitors) are analysed for the amplitude and phase of maximum intensity of the 24 h variation at the geomagnetic equator and at 48‡ N. The same analysis is performed on selected charged particle detectors. The analysis covers 1953–55, which includes the time of solar cycle (sunspot) minimum in 1954. During 1954 it is known that the 24 h variation possesses an anomalous behaviour. It is shown that during 1954 there is an interval of 9 months or more when the solar daily variation appears to undergo a progressive phase shift whose time of maximum lies in the range of 0800–1000 h on a sidereal time scale. This anisotropy certainly exists in the radiation falling upon the atmosphere, and it is likely, although not proven, that the anisotropy prevails even outside the terrestrial field. The question of whether this sidereal effect is spurious or real is discussed in relationship to the recent results on the modulation of cosmic ray intensity within the solar system.