| Summary: | A novel scattering theory is implemented to produce a fully three-dimensional model of VLF scattering caused by precipitation events within the D-region. This model is not limited by the WKB approximation as are many of the previous models, and offers a unique tool for investigating the 'Trimpi' effect. The model imposes no limitations upon the model mixing within the scattering region, and uses a multimodal propagation package (LWPC) to provide accurate field values as inputs to the scattering process. Results concerning changes in δN e , and other non-spatial parameters are discussed, as are the limitations of the Born approximation, which constrain the range of δN e that can be modelled. The influence of the precipitation patch diameter and depth are also investigated, and it is shown that the diameter shows a cubic dependence on the total scattered power, and a linear proportionality for the depth. Polar plots are presented, which demonstrate the narrowing of the main lobe of the forward-scattered signal as the patch diameter is increased. Precipitation patch locations, both on and off the GCP are considered and compared with the experimental results observed by other research groups. The model results indicate a region within 200 km of the GCP, and extending up to 2-4 Mm from either the transmitter or the receiver along the GCP, within which precipitation would be expected to produce detectable Trimpi with typical receiver sensitivities. This work is extended to model the data obtained during a campaign at Rothera ( L =20.8) and Faraday ( L =2.4) in the Antarctic, indicating likely precipitation regions and patch diameters. Further, the model is also used to investigate the rapid decrease in Trimpi occurrence with increasing L shell observed in the data. This leads to extensions to the model which presents a possible mechanism to explain the observed decrease in Trimpi.
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