The measurement of proton flux reaching and sustaining ~ 10 p.f.u. (1 p.f.u. = 1 particle cm-2 s-l sr-1) for at least 15 min. at energies > 10 MeV by the primary NOAA geosynchronous satellite. The start time of the event is defined as the earliest time at which event thresholds have been reached. The end time is the last time 10 p.f.u. was observed. This definition allows multiple injections from flares and interplanetary shocks to be encompassed by a single event.