Since IGY period (1957-58), natural and artificially produced Very Low Frequency ( VLF) electromagnetic radiations are being recorded at large number of ground stations and on board satellites to study various wave-plasma interactive phenomena. International Nuclear Information System (INIS) In order for this option to be resolved we need more studies using highly sensitive optical systems capable of detecting weaker sprites, sprite halos and elves. Since the great majority of the early events not accompanied by sprites was caused by positive cloud to ground (+CG) lightning discharges, it is possible that sprites or sprite halos were concurrently present in these events as well but were missed by the sprite-watch detection system. This is because the number of early events detected in some cases was considerably larger than the number of sprites. However, the one-to-one "sprite to early" event relationship, if viewed conversely as "early to sprite", appears not to be always reciprocal. This implies that the sprite generation mechanism may cause also sub-ionospheric conductivity disturbances that produce early VLF events.
The evidence shows that sprites are accompanied by early VLF perturbations in a one-to-one correspondence. In this setup, the multiple links act in a complementary way that makes the detection of early VLF perturbations much more probable compared to a single VLF link that can miss several of them, a fact that was overlooked in past studies. The present study resolves these large discrepancies by analyzing several case studies of sprite and narrowband VLF observations, in which multiple transmitter- receiver VLF links with great circle paths (GCPs) passing near a sprite-producing thunderstorm were available. Past studies have shown a correlation between sprites and early VLF perturbations, but the reported correlation varies widely from ~ 50% to 100%. Haldoupis, Christos Amvrosiadi, Nino Cotts, Ben van der Velde, Oscar Chanrion, Olivier Neubert, Torsten Sprites and Early ionospheric VLF perturbations Using the assembled receiver, some of the transmissions, including the Omega W/L at . Signal field strengths of various stations were estimated, and a suitable radio receiving system was set up to receive them. This study is on the receivability of some standard time and frequency signals in the VLF range in Zaria, Nigeria. Investigation of the receivability of VLF standard time and frequency. VLF receivers must selectively filter out unwanted emissions and amplify the filtered signal to a record-able level without degrading the quality. Natural emissions can also be detrimental to the quality of recordings as some of the more interesting natural emissions such as whistlers or auroral chorus may be drowned out by the more common sferic emissions. These can occur from man made sources such as power line hum, which can be prevalent for many harmonics after the fundamental 50 or 60 Hz AC source or from VLF radio transmissions such as LORAN, used for navigation and communications. Unwanted emissions or signal noise is a major problem for VLF radio receivers.
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