Caracterização dos parâmetros de eventos de ondas de gravidade na ionosfera utilizando VLF
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Tipo
Dissertação
Data de publicação
2019-06-10
Periódico
Citações (Scopus)
Autores
Raunheitte, Luís Tiago Medeiros
Orientador
Correia, Emilia
Título da Revista
ISSN da Revista
Título de Volume
Membros da banca
Silva, Luciano
Bageston, José Valentin
Bageston, José Valentin
Programa
Ciências e Aplicações Geoespaciais
Resumo
Ondas de Gravidade (OGs) vem sendo investigadas principalmente com o uso de imageadores all-sky de airglow, capazes de detectar suas características a aproximadamente 90 km de altura com uso do filtro da hidroxila (OHNIR). Nesta pesquisa busca-se investigar OGs através da sua interação com a base da Ionosfera, região D, e para tanto foram utilizadas medidas feitas com receptores de rádio de frequências muito baixas (do inglês, Very Low Frequency, VLF) obtidas na Estação Antártica Comandante Ferraz (EACF), localizada na ilha Rei George. A passagem de OGs pela base da Ionosfera resulta em perturbações oscilatórias na densidade de elétrons, que são detectadas como flutuações na amplitude dos sinais VLF, cuja caracterização é feita por meio da análise Wavelet (Morlet). Neste estudo utilizamos dados VLF recebidos na EACF advindos das estações emissoras NAA (Estação de Arlington) na costa leste dos EUA e da NPM (Estação de Pearl Harbor) no Havaí. Estes trajetos foram escolhidos por compreenderem a região entre o extremo sul da América do Sul e a Antártica, conhecida como Estreito de Drake, onde há grande atividade de OGs, assim como a região da Cordilheira dos Andes, com grande potencial para geração de ondas por efeitos orográficos. As oscilações da amplitude do sinal VLF refletem o período das OGs ao passarem na base da Ionosfera, e estes períodos são comparados com as propriedades das OGs mesosféricas, originalmente observadas com câmeras all-sky. Esta técnica foi primeiramente validada por meio de estudos de caso que mostraram uma boa associação dos períodos observados de OGs identificadas via técnica VLF com as observadas através de airglow. A análise estatística da ocorrência das OGs detectadas com o VLF no decorrer do ano de 2007 mostrou que elas apresentam períodos distribuídos entre 5 e 45 min, com alguns casos de períodos acima de uma hora, mas com predominância entre 5 e 20 min. Quanto a sazonalidade de ocorrência das ondas de gravidade, a detecção de atividade de ondas ocorreu em mais de 87% dos dias dos meses de março a outubro, em cerca de 80% dos dias nos meses de janeiro e dezembro e em cerca de 60% dos dias em fevereiro e novembro. As ondas com períodos de 5 a 25 min apresentaram maior ocorrência nos equinócios (março e setembro), enquanto que as ondas com período maiores que 25 min ocorreram preferencialmente nos solstícios (janeiro e julho).
Gravity Waves (GWs) are mostly investigated using airglow all-sky imagers fitted with hydroxyl (OHNIR) filter, which give their characteristics at about 90 km height. Here we will investigate their impact on the base of the ionosphere, at D-region, utilizing very low frequencies (VLF) radio measurements performed at the Brazilian Antarctic Station Comandante Ferraz (EACF) on King George Island. The passage of GWs through the base of the ionosphere results on oscillatory perturbations of the electron density that are detected as amplitude fluctuations of the VLF signals, wich characterization were done through the Morlet’s Wavelet analysis. In this study has been utilized VLF data received at EACF emitted from West Coast of the USA, NAA (Arlington Station), and at Hawaii, NPM (Pearl Harbor Station). These trajectories were chosen because it passes by the Drake’s Passage, region between the tip of the South America and Antarctica peninsula, this region is pointed as one of the most active region of GWs, as well as aside of Andes Mountains a region of great potential to generate waves by orographic effects. The amplitude oscillations of the VLF signal reflect the GWs periods passing through the ionosphere base and these periods has been compared to the ones obtained from airglow observations originally made with all-sky imagers. This technique was first validated by case studies that presented good association between the periods observed from GWs obtained using VLF technique and using airglow observations. The statistics analysis of the occurrence of GWs detected with VLF along the year showed that they present periods distributed between 5 and 45 min with only some cases over one hour, and predominance between 5 and 20 min. About the seasonal occurrence of gravity waves, the detection of waves activity occurred in more than 87% of the days between March to October, in 80% of the days among January and December and in 60% of the days in February and November. The waves between 5 min and bellow 25 min presented predominance on the equinoxes (March and September) and with periods over 25 min occurred preferably in the solstices (January and July).
Gravity Waves (GWs) are mostly investigated using airglow all-sky imagers fitted with hydroxyl (OHNIR) filter, which give their characteristics at about 90 km height. Here we will investigate their impact on the base of the ionosphere, at D-region, utilizing very low frequencies (VLF) radio measurements performed at the Brazilian Antarctic Station Comandante Ferraz (EACF) on King George Island. The passage of GWs through the base of the ionosphere results on oscillatory perturbations of the electron density that are detected as amplitude fluctuations of the VLF signals, wich characterization were done through the Morlet’s Wavelet analysis. In this study has been utilized VLF data received at EACF emitted from West Coast of the USA, NAA (Arlington Station), and at Hawaii, NPM (Pearl Harbor Station). These trajectories were chosen because it passes by the Drake’s Passage, region between the tip of the South America and Antarctica peninsula, this region is pointed as one of the most active region of GWs, as well as aside of Andes Mountains a region of great potential to generate waves by orographic effects. The amplitude oscillations of the VLF signal reflect the GWs periods passing through the ionosphere base and these periods has been compared to the ones obtained from airglow observations originally made with all-sky imagers. This technique was first validated by case studies that presented good association between the periods observed from GWs obtained using VLF technique and using airglow observations. The statistics analysis of the occurrence of GWs detected with VLF along the year showed that they present periods distributed between 5 and 45 min with only some cases over one hour, and predominance between 5 and 20 min. About the seasonal occurrence of gravity waves, the detection of waves activity occurred in more than 87% of the days between March to October, in 80% of the days among January and December and in 60% of the days in February and November. The waves between 5 min and bellow 25 min presented predominance on the equinoxes (March and September) and with periods over 25 min occurred preferably in the solstices (January and July).
Descrição
Palavras-chave
ondas de gravidade , VLF , airglow
Assuntos Scopus
Citação
RAUNHEITTE, Luís Tiago Medeiros. Caracterização dos parâmetros de eventos de ondas de gravidade na ionosfera utilizando VLF. 2019. 62 f. Dissertação (Mestrado em Ciências e Aplicações Geoespaciais) - Universidade Presbiteriana Mackenzie, São Paulo, 2019.