VLF line radiation observed by satellite

VLF line radiation received by the ISIS 1 and 2 satellites over New Zealand is found to fall into two distinct classes. The first of these consists of magnetospheric lines (MLs) which are characterized by a broadband appearance and by frequency drifts of a few tens of hertz per minute, similar to those reported elsewhere. Both their initial frequencies and their frequency spacings were, however, found to be essentially random rather than multiples of 50 or 60 Hz. The hourly variation in ML occurrence showed no correlation with electrical load in possible electrical mains systems sources. No clear decrease in occurrence on weekends was evident. This first satellite survey with significant numbers of MLs found no evidence of a relationship with power line harmonics. The second class of satellite‐received VLF lines consists of “tram lines” (TLs) which are characterized by their very narrow bandwidth and zero frequency drift. TLs appear to lie close to harmonics of 50 or 60 Hz. An example of this class is presented.