Long-term association of solar activity and cosmic ray intensity for solar cycles 21 and 22

65-69Based on the monthly data of solar flare index (SFI), instead of sunspot numbers and cosmic ray intensity (CRI) for the last two solar cycles since 1976, a detailed correlative study has been made by using the ‘‘running cross-correlation’’ method. It has been found that the anti -correlation between SFI and CRI is strong during ascending and descending phases of the solar cycle. The observed cosmic ray modulation during these periods, when compared with other solar activity indices, shows the appropriateness of the SFI as solar activity index, instead of sunspot numbers or even the grouped solar flares (GSF). The effects are found to be distinctly different in the two solar cycles 21 and 22, when the most appropriate solar activity index SFI is used. The observed depth of cosmic ray modulation in cycle 22 is larger than that in cycle 21 in contrast to reverse tendency in SFI, which necessitates further studies on short -term basis