The ULF modulation of ELF-VLF emissions close to the magnetospheric boundary

The spatial extent and temporal behaviour of quasi-periodic (QP) intensity modulations of 0.5-2kHz ELF-VLF emissions were investigated in a comparative study of data collected at three Antarctic stations. Frequently, the waveforms of the ELF-VLF signals received at each site were identical. The emissions are identified with the periodic modulation of the electron pitch-angle distribution by the propagation of ULF compressional fast-mode waves through a region. In addition to generation close to the equatorial plane, we propose an additional high-latitude source of QP emissions. These emissions are associated with regions of minimum-B produced by the dayside compression of the magnetosphere close to the magnetopause.