A study of quasi-periodic ELF-VLF emissions at three Antarctic stations: evidence for off-equatorial generation?

• Published in: Annales Geophysicae
• Main Authors: Morrison, K., Engebretson, M. J., Beck, J. R., Johnson, J. E., Arnoldy, R. L., Cahill ,Jr, L. J., Carpenter, D. L., Gallani, M.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Springer Verlag 1994
• Subjects: article; Verlagsveröffentlichung; Antarctic; The Antarctic; South Pole; Siple; Antarc*; South pole
• Online Access: https://doi.org/10.1007/s00585-994-0139-8; https://noa.gwlb.de/receive/cop_mods_00038158

The spatial extent and temporal behaviour of quasi-periodic (QP) intensity modulations of 0.5-2 kHz ELF-VLF signals were investigated in a comparative study of data collected at the Antarctic stations of South Pole (L=14), Halley (L=4), and Siple (L=4). Frequently, the waveforms of ELF-VLF signals simultaneously received at each site were identical. Although of similar frequency structure, the waveforms of the accompanying Pc3 magnetic pulsations did not show a one-to-one association. Whereas both are dayside phenomena, QP emissions occur over a smaller range of local times, and have a maximum of occurrence later in the day closer to local noon. QP 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. However, contrary to previous ideas, rising-tone emissions do not represent the frequency-time signatures of such waves. 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. Model magnetic field calculations of these minimum-B regions as a function of magnetic local time and invariant latitude are presented.