A COMPARISON OF MIDLATITUDE PI-2 PULSATIONS AND GEOSTATIONARY ORBIT PARTICLE INJECTIONS AS SUBSTORM INDICATORS

Both the injection of energetic particles at geostationary orbit and g round magnetic observations of Pi 2 wave activity are characteristic i ndicators of the onset of the substorm expansion phase. Occurrence sta tistics for the appearance of electron and proton particle injection a t three geostationary spacecraft and for the detection of midlatitude magnetic Pi 2 pulsations in a 3-hour local time sector have been compi led from 240 hours of data. Throughout this interval a signature was d etected on one or more of the instruments on average every 65 min. It is demonstrated that the detection of geostationary orbit particle inj ections and the detection of ground-based Pi 2 pulsations are correlat ed at a very high significance level, and that both appear to be effec tive substorm indicators. However, a small percentage of events (appro ximately 10% in each case) may be identified as a Pi 2 event but not a s an injection event or viceversa, without any obvious explanation, su ch as the local time of the observing instrumentation. A number of pos sible explanations for the discrepancies between the two data sets are discussed.