Caracterização dos parâmetros de eventos de ondas de gravidade na ionosfera utilizando VLF

• Autor(a) principal: Raunheitte, Luís Tiago Medeiros
• Data de Publicação: 2019
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Biblioteca Digital de Teses e Dissertações do Mackenzie
• Texto Completo: http://dspace.mackenzie.br/handle/10899/24142
• topic: ondas de gravidade; VLF; airglow; CNPQ::CIENCIAS EXATAS E DA TERRA::GEOCIENCIAS::GEOFISICA

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passing through the ionosphere base and these periods has been compared to the ones obtained from airglow observations originally made with all-sky imagers.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).