Observações de longo prazo de ondas de gravidade de média escala sobre a região equatorial brasileira.

Abstract

This project has studied the long term observations of medium-scale gravity waves over Brazilian equatorial region. As part of this objective,11 years (2000 to 2010) all-sky image measurements of mesospheric gravity waves were made successfully from Sao Joao do Cariri (7.40oS,36.50oW) of the magnetic equator. The long term observation provided continuous measurements of the medium scale-gravity waves characteristic structures to be analyzed. Keograms analysis was used to determine the arameters of 537 medium-scale gravity waves observed in the OH emission at 87km altitude.The characteristics were studied as well as the seansonality of the phase propagation direction, and the evolution of the MSGWs according to the solar cycle. The maximum horizontal wavelength, observed period and the phase speed were concentrated between 100 to 150km, 20 to 40m/s and 60 to 80 minutes, respectively. The total anisotropy of the propagation direction were preference to Northeast of the site and was more signi cant during Spring and Summer seasons, however autumn and winter were evenly propagated. The critical layer theory for gravity wave filtering was applied to 2003 dataset to study the effects of middle atmospheric winds on the propagation of medium-scale gravity waves. And it was found that these waves were less susceptible to wind filltering effects especially during summer season. It was also observed that some of the medium-scale were capable of propagating into the lower thermosphere where they may have acted directly as seeds for the Rayleigh-Taylor instability development. There was no direct correlation between the evolution of the MSGWs and the solar cycle activity, therefore, it can be concluded that, the wave events were primarily generated in Brazil equatorial region by meteorological processes. Finely, it was affirmed that keogram methodology appear as a good tool to study the spectral characteristics of MSGWs in the MLT since the results are in consistence with the literature.