Abstract. On 8 April 2005, strong gravity wave (GW) activity (over a period of more than 3 h) was observed in São João do Cariri (7.4∘ S, 36.5∘ W). These waves propagated to the southeast and presented different spectral characteristics (wavelength, period and phase speed). Using hydroxyl (OH) airglow images, the characteristics of the observed GWs were calculated; the wavelengths ranged between 90 and 150 km, the periods ranged from ∼26 to 67 min and the phase speeds ranged from 32 to 71 m s−1. A reverse ray-tracing analysis was performed to search for the possible sources of the waves that were detected. The ray-tracing database was composed of temperature profiles from the Naval Research Laboratory Mass Spectrometer Incoherent Scatter (NRLMSISE-00) model and SABER measurements as well as wind profiles from the Horizontal Wind Model (HWM) and meteor radar data. According to the ray tracing result, the likely source of these observed gravity waves was the Intertropical Convergence Zone, which caused intense convective processes to take place in the northern part of the observatory. Also, the observed preferential propagation direction of the waves to the southeast could be explained using blocking diagrams, i.e. due to the wind filtering process.

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