Long-period magnetic activity during the May 15, 1997 storm

The behavior of ULF activity in the Pc5-6/Pi3 band (1-7 mHz) on a global sc ale during the main phase of the intense magnetic storm on May 15, 1997, is studied using data from stations in the INTERMAGNET, Greenland Coast Array , IMAGE, and CPMN (210 MM) networks. Two regions of long-period broad-band ULF intensification are observed during the magnetic storm: one is in the e arly morning hours, the other is near dusk. The first one is, probably, rel ated to an energetic electron injection, whereas the other one is due to th e injection of ring current protons. It is suggested that ULF waves may be an intermediate agent transferring energy from the ring current protons/ele ctrons to the relativistic electrons. The azimuthal scale of ULF disturbanc es in the dusk sector as determined from the IMAGE array was about 500 km, which is an order of magnitude less than had been often assumed in modeling of resonant electron acceleration by MHD waves. The features of the observ ed broad-band ULF oscillations impose some constraints on models of relativ istic electron acceleration by MHD waves during magnetic storms. (C) 2001 E lsevier Science Ltd. All rights reserved.