Magnetospheric VLF line radiation.

Magnetospheric VLF Line Radiation (MLR) is a broad band VLF emission (typically 1 kHz wide centered on 3 kHz) which has line structure in its spectrum. The events studied were received during 1977-80 at Halley, Antarctica and also in the geomagnetically conjugate region (Newfoundland). The occurrence of Halley MLR events as a function of local time and geomagnetic activity and the differences in MLR activity between Halley and SipLe, Antarctica are discussed. An MLR event received on 26 June 1978 may be the result of magnetospheric amplification of VLF radiation of harmonics from electrical power lines (PLHR) in the conjugate region; the radiated power required was estimated to be 50 mW. Most Halley MLR events do not have any direct relation with PLHR although in several of the generation mechanisms discussed PLHR may have an indirect role.
A series of measurements of the electromagnetic field near to several power transmission Lines in Newfoundland were made to determine the magnitude of the unbalanced harmonic currents and the skin depth in the ground, which in turn were used to estimate the strength of PLHR entering the magnetosphere. The largest radiated power determined for a single line was 500 nW in the range 2.7 to 3.7 kHz although much Larger powers may be radiated from the more industrialised regions further west.
A description of the VLF receiver and some improvements made to it is given followed by a review of spectrum analysis techniques and a description of some methods used for the work on PLHR and MLR.