The Forbush decrease of February 1978.

Certain features of a large Forbush decrease recorded by neutron monitors at three Australian sites are discussed. The decrease was among the largest yet observed, amounted to about 23% near sea level, and was characterized by a 'predecrease' of about 5% before the rapid decrease occurred. This predecrease was observed only at the southernmost sea-level site and is attributed to an effect confined to particles having a rigidity of no more than about 7 GV. It is noted that the solar flare believed to have been responsible for this event was uncharacteristically accompanied by a Type II radio burst and that relativistic solar particles were not responsible for the event.