Is magnetospheric line radiation man-made?

Magnetospheric line radiation (MLR) events are relatively narrowband VLF si gnals (similar to 30 Hz) that sometimes drift in frequency and that have be en observed in both ground-based and satellite data sets. We present the re sult of a survey undertaken on the basis of measurements made of MLR events observed at Halley station, Antarctica (75 degrees 35'S, 26 degrees 33'W, L approximate to 4.3) during June, July, September, and December 1995, spec ifically to examine whether there is a link between MLR and power line harm onic radiation (PLHR). We find that (1) the diurnal variation of MLR occurr ence at Halley does not resemble the expected load pattern in the industria lized 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 ro North American electrical load; (3) MLR does not show an immediate association with geomagnetic activity, as would be expected fr om increases in PLHR levels produced by geomagnetically-induced currents sa turating transformers; and (4) there is no evidence of a Sunday, weekend, o r 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 ca used by PLHR. In addition, Halley data have been examined to determine whet her the intensity of all types of VLF emissions are influenced by PLHR. We find that (1) there is no significant difference between weekdays and weeke nds over the frequency range 0.5-9.3 kHz and (2) there is no consistent cha nge in wave intensity that is observed around any of the major North Americ an holiday periods. It is concluded that PLHR is not a significant influenc e on geospace as viewed from Halley.