Magnetospheric line radiation (MLR) events are relatively narrowband VLF signals (∼30 Hz) that sometimes drift in frequency and that have been observed in both ground-based and satellite data sets. We present the result of a survey undertaken on the basis of measurements made of MLR events observed at Halley station, Antarctica (75°35'S, 26°33'W, L≈4.3) during June, July, September, and December 1995, specifically to examine whether there is a link between MLR and power line harmonic radiation (PLHR). We find that (1) the diurnal variation of MLR occurrence at Halley does not resemble the expected load pattern in the industrialized conjugate hemisphere; (2) MLR does not show the pronounced east-west asymmetry in the distribution of arrival directions which would be the case if it was linked to North American electrical load; (3) MLR does not show an immediate association with geomagnetic activity, as would be expected from increases in PLHR levels produced by geomagnetically-induced currents saturating transformers; and (4) there is no evidence of a Sunday, weekend, or other 7-day cycle in the occurrence of MLR. Taken together these results strongly suggest that MLR is a natural VLF emission and is not primarily caused by PLHR. In addition, Halley data have been examined to determine whether the intensity of all types of VLF emissions are influenced by PLHR. We find that (1) there is no significant difference between weekdays and weekends over the frequency range 0.5–9.3 kHz and (2) there is no consistent change in wave intensity that is observed around any of the major North American holiday periods. It is concluded that PLHR is not a significant influence on geospace as viewed from Halley.
Authors: Rodger, Craig J., Clilverd, Mark A., Yearby, Keith H., Smith, Andy J.