Propagação guiada de ondas de VLF: aplicação ao estudo de fenômenos atmosféricos e naturais

• Ano de defesa: 2012
• Autor(a) principal: Cardenas, Jorge Enrique Samanes
• Orientador(a): Raulin, Jean Pierre
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Presbiteriana Mackenzie
• Palavras-chave em Português: VLF (Very Low Frequency); terminadouro; conversão modal; efeitos sismo-eletromagnéticos
• Palavras-chave em Inglês: VLF (Very Low Frequency); terminator line; modal conversion; seismic-electromagnetic effects
• Área do conhecimento CNPq: CNPQ::ENGENHARIAS::ENGENHARIA ELETRICA::TELECOMUNICACOES
• Link de acesso: http://dspace.mackenzie.br/handle/10899/24332

Deep amplitude minima are observed in the daily records of Very Low Frequency (VLF, between 3 - 30 kHz) wave amplitudes. Amplitude minima are attributed to modal interference and modal conversion of waves propagating in the Earth - Ionosphere waveguide. The time of amplitude minima is related with the localization of the Terminator line and, therefore, is denominated of Terminator Time or TT time. In this work, we developed a methodology based on the monitoring of TT time to infer the distance of modal interference D and its temporal variation in relation to atmospheric and natural phenomena. For this purpose, we used data provided by the South America VLF Network (SAVNET) to the period 2007 - 2011. The results showed that the methodology is a promising tool to study the dynamics of the lower ionosphere, by means of the daily values of the undisturbed nighttime ionospheric height(hN). We identified short-term and long-term time variations of hN, where the long-term variation is possibly related with the solar activity cycle. We propose the use of this method to search for seismic- electromagnetic effects, and that it should be applied to medium and short propagation paths. Using the Long Wave Propagation Capability (LWPC) code, we simulated TT times and the results show good agreement with the observations, so a value for nighttime height hN = 88 km is suggested. This work will contribute to a greater viability of the use of the VLF technique for the study of the lower ionosphere and the forcings acting on this region of the atmosphere.