Some properties of flare-not-associated Forbush decreases

Abstract

All the flare-not-associated Forbush decreases (NAFDs) are investigated over the period 1975–1979. The connection between the NAFDs occurrence and the central meridian passage of strong active regions producing great flare-associated FDs confirms the flare origin of the NAFDs. The interplanetary perturbations at the eastern and western boundaries of the modulated region are found to be long-living corotating structures. These structures seem to mark also the boundaries of the region in which the (1⤜4) MeV protons accelerated by interplanetary flare-generated shocks are confined.