The 27-day variation in cosmic ray intensity

Abstract

The following facts emerge from the study: 1) In general there is a negative correlation betweenI, the cosmic ray intensity, andK bp the planetary index, although there are exceptions. 2) There is a positive correlation between the relative decrease in intensity, —I/It and the planetary index,K bp . There are exceptions during the low sunspot activity period of 1949 ÷ 54. 3) TheK bp minimum (or maximum) is observed to precede the corresponding cosmic ray one in some years and follow in other years. But it appears that the latter case is generally found during the rising part of the solar cycle and possibly during the early fall. 4) There is clear evidence that the amplitude of the 27 day variation in cosmic ray intensity follows the geomagnetic disturbance better than the solar activity. Both of them exhibit similar departure from solar activity during 1946 ÷ 52. 5) The time of maximum of the diurnal variation of cosmic ray intensity on disturbed days follows the geomagnetic disturbance better than the solar activity. The semidiurnal time of maximum on disturbed days appears to follow the solar activity in a rough measure.