The apparent sidereal daily variation of cosmic ray intensity during the recent sunspot minimum

The unusually large changes of phase which occurred in the cosmic ray solar daily variation during the year 1954 have been found by Conforto and Simpson (1957) to simulate strong sidereal daily variations. These authors have suggested that their results represent a genuine sidereal effect which is observable only during periods of extremely low solar activity, as in 1954. A systematic search for sidereal effects during this year has been made using the results from the Carnegie Institution stations as well as Colombo, Hobart and Tokyo. Although no significant sidereal effects were seen at Colombo, the other data show substantial sidereal daily variations with a remarkable consistency in phase. The time of maximum at the equator was 19 hr L.Sid.T. while at higher latitudes it was about 22 hr L.Sid.T. The character of the solar diurnal variations and the relations between their seasonal changes and sidereal daily variations are discussed and it is concluded that at least a part of the observed sidereal effects were spurious.