spaceweb@oulu.fi - last update: 5 January 1999, 1530 UT (RR) . Pi1 are irregular ULF range (T = 1 - 40 s) magnetic pulsations that can be divided into two groups, Pi1 B and Pi C , i.e., into burst like and continuous (Heacock, 1967). There are two maxima in the occurrence rate, on midnight and on pre-noon. The midnight pulsations contain both Pi1 B and Pi C flavours, while the prenoon pulsations are all of continuous type. Heacock, R. R., Two subtypes of Pi micropulsations, J. Geophys. ...