Magnetospheric line radiation observations at Halley, Antarctica

Magnetospheric line Radiation (MLR) events are relatively narrowband VLF si gnals that sometimes drift in frequency, and have been observed in both gro und based and satellite data sets. Line radiation has been attributed by so me authors to be power line harmonic radiation (PLHR), generated from harmo nics of the power transmission frequency (50 or 60 Hz) and radiated into th e ionosphere and magnetosphere by long power lines. We present the result o f a survey undertaken on the basis of measurements made of MLR events obser ved at Halley station, Antarctica (75 degrees 30'S, 26 degrees 54'W, L appr oximate to 4.3) in part of June 1995. Particular attention is given to the frequency spacing, drift rates, and amplitude of the MLR lines. MLR is pres ent in 7.0% of the minute-long VLF recordings made at Halley. The MLR lines rise in frequency as often as they fall. However, these lines do not neces sarily rise or fall monotonically and can oscillate while drifting. The Hal ley MLR has a wide range of line spacings and does not preferentially show spacings near harmonics of electrical transmission frequencies, either 50 H i or 60 Hz. There is no correlation between the frequency drifts of the loc al 50 Hz Halley electrical supply and those of the observed MLR lines. The distribution of MLR line spacings observed in the Halley data has a roughly exponential form, suggesting a different mechanism for MLR than for PLHR.