Forbush-decreases in 19th solar cycle

Abstract

The abnormally high solar activity was observed in the late 50's – the early 60's of the 20th century, but not many possibilities was available that time of its observation to which we have got in use during the last years. Ground level cosmic ray observations, along with geomagnetic activity, are one of a few kinds of the continuous measurements, allowing to judge on the events of 19th cycle. The IZMIRAN Database in which all Forbush-decreases are collected since July, 1957 has been used for the analysis. To make the statistics of 19th cycle fuller, the catalogue by Lockwood containing rather big Forbush-decreases (>3 %), picked out from the data of one neutron monitor (Mount Washington), was involved. Comparison of the events in cosmic rays with solar and geomagnetic activity has shown that the quantity and intensity of geomagnetic storms in 19th cycle correspond to abnormally high number of the sunspots. However in this cycle there is a certain deficiency of Forbush-effects of the large size. Apparently, deficiency of the big Forbush-decreases during this period means that coronal mass ejections (CMEs/ICMEs) in the 19th cycle distinguished from later CMEs and differently affected of the cosmic ray modulation and geomagnetic activity. Probably, the most powerful CMEs of the 19th cycle had, as a whole, the smaller size, than the greatest emissions of solar plasma in later period.