Pi 2 micropulsations as indicators of substorm onsets and intensifications

In this paper we shall demonstrate the relationship between Pi 2 bursts and substorm onsets and intensifications. We shall show that the degree of spatial localization of the Pi 2 disturbance often makes it unidentifiable at middle and lower latitudes using conventional recording techniques. Thus while the presence of a Pi 2 pulsation may be taken as an indication of substorm occurrence, its absence at a particular station may be due to the location of the station relative to the substorm region and may not necessarily imply the absence of substorm activity. Sonograms from an east-west array of observatories in the auroral oval will be employed to demonstrate the use of Pi signals at auroral zone latitudes to define the times of substorm onsets and intensifications. It is recommended that the present subjective means of identifying Pi 2's be replaced by more objective criteria, based upon careful analysis of Pi 2 signals. (author)