Effects of active solar regions on the galactic cosmic ray intensity

During the year 1969 two long-lived centres were active on the Sun at Carrington longitudes 50° < L < 100° and 250° < L < 300°. About 80% of the flares of importance 1B, produced during this period, originated in these zones.The solar modulation of galactic cosmic ray intensity during 1969 was dominated by effects resulting from the activity in the two zones. In fact all the decreases can be related to the passage at the central meridian of the active centres. Persistence of the effects connected to solar regions is found also during rotations in which they do not produce flares in front of the Earth.Seventeen among the twenty-six intensity decreases, observed during this period, can also be correlated to individual flares belonging to the region at central meridian (longitudes ± 40° with respect to the CM).The data suggest that two phenomena are operative to produce decreases of the cosmic ray flux: the passage of the interplanetary corotating stream associated with the active region near the central meridian and the blast wave produced by the flares in front of the Earth.