Solar cycle phenomena in cosmic ray intensity up to the recent solar cycle

A systematic correlative study has been performed since long to establish a significant relationship between cosmic ray intensity and different solar/heliospheric activity parameters and study is extended to recent solar cycle 23. In the present work yearly average of sunspot number (Rz), interplanetary magnetic field (B) have been used to correlate with yearly average cosmic ray intensity derived from the data of Moscow neutron monitor. It is noticed that for four different solar cycles 20-23 the cosmic ray intensity is found to anti-correlated with sunspot numbers (Rz) and interplanetary magnetic field (B) with some discrepancy. However, the interplanetary magnetic field B shows a good positive correlation with Rz for four different solar cycles. The interplanetary magnetic field strength (B) shows a weak negative correlation (−0.35) with cosmic rays for the solar cycle 20, whereas it shows a high anti-correlation for the solar cycles 21-23 (−0.76,−0.69). Modulation of cosmic rays during solar cycle 20 (1964-1976) presents discrepancies regarding the importance of IMF B for long-term modulation at 1 AU for the cycle 20. A significant contribution to modulation from the termination shock during solar cycle 20 could dilute the correlation of cosmic rays with the interplanetary magnetic field B at 1 AU for that cycle. The perturbations of the heliosphere is weaker and less widely spread during solar cycle 20 than during other solar cycles. This might lead to a situation where the heliospheric perturbations are relatively small for cosmic ray particles allowing these particles to reach the Earth as if it was a minimum solar activity period. This implies that the heliospheric perturbations caused by solar activity in the descending phase of solar cycle 20 were quite local and could not result in global modulation of cosmic rays. These results demonstrate that the heliosphere evolved to the quite time structure very early in the declining phase of the solar cycle 20, implying an exceptionally fast recovery of the cosmic ray level and a long flat cosmic ray maximum during 1972-1977. This exceptional heliospheric evolution led to the negative lag between cosmic ray and solar activity cycle observed in the declining phase of the solar cycle 20.