Change in the eleven-year modulation at the time of the June 8, 1969, Forbush decrease.

The functional form of the modulation for the 11-year variation changed abruptly after the Forbush decrease of June 8, 1969. This change in the 11-year modulation suggests that this Forbush decrease was an integral part of the 11-year variation. Some details of the change as observed by neutron monitors and by spacecraft at low energies are discussed.