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A study of whistlers and related VLF phenomena.

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Whistlers are naturally occurring Very Low Frequency (VLF) phenomena which are the result of lightning-radiated electromagnetic waves propagating in Earth’s plasma environment. Major research into whistlers and their generation began in 1951 and since then much has been discovered about them. This has allowed whistlers to be used as magnetospheric probes. Many issues concerning whistlers are still disputed, however, such as the relationship between the lightning location and the conjugate point of the receiver. A correlation between whistlers detected by the DEMETER satellite above South Africa and lightning located by WWLLN was used to determine the source region for these whistlers. The whistlers were found to originate from lightning strokes as far away as 10000 km. This result is statistically significant. During the course of this research an interesting observation of chorus was made on Marion Island. Since this was the first observation of chorus made on the sub-antarctic Marion Island, conditions surrounding the event were studied in great detail. This led to several interesting observations about the nature of this observation. In particular, during the evolution of the emission, it transformed to hiss, which makes this observation relevant to recent results suggesting that hiss is generated by chorus. It was also found that Marion Island was close to the plasmapause during the observation, which has further implications related to the chorus-hiss relationship. A study of the occurrence of twin whistlers received at Rothera and SANAE IV was conducted. These were whistlers which had propagated from a single ionospheric exit point to both receivers. Rothera and SANAE IV share the same whistler source region, yet the average number of whistlers received at Rothera is an order of magnitude greater than that received at SANAE IV. The twin whistler analysis showed that the most probable reason for this disparity is that whistlers from the source region enter the waveguide preferentially closer to Rothera, making it more likely for them to be received at Rothera than SANAE IV. These results have implications on the nature of sub-ionospheric propagation of whistlers, which is not the same as that of spherics. Finally, a method for tracking tropical cyclones using lightning locations from WWLLN was developed. During the course of this thesis, tropical cyclone Irena was the result of damage on the east coast of South Africa. This presented an opportunity to investigate the ability of WWLLN data to describe the passage of these destructive phenomena near South Africa. The details of this new method are discussed. While the algorithm developed has room for improvement, its performance was tested on the recent tropical cyclone Irina which occurred during 2012.


Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.


Whistlers (Radio meteorology), Lightning., VLF emissions., Theses--Physics.