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The terrestrial atmosphere is a dynamical system in which periodic oscillations are present and play a significant role in the dynamics of the upper mesosphere and low thermosphere (MLT). It is already well known that atmospheric tides play an important role in the dynamics of the MLT region, and the purpose of this study is to extend our knowledge of diurnal and semidiurnal oscillations in the equatorial MLT, taking advantage of the measurements of meteor winds over Sao Joao do Cariri, Brazil (7oS, 36oW), obtained from August 2004 to August 2005. In a preliminary analysis, we have observed that both zonal and meridional wind components exhibited variability with respect to both time and height. The prevailing zonal wind shows a structure characterized by a semiannual oscillation (SAO) and are westward most of the time. The prevailing meridional wind is weaker than the zonal and exhibit an annual cycle. Diurnal and semidiurnal meridional wind oscillations also exhibit time and height variability. In general, the diurnal and semidiurnal amplitudes for the meridional wind component were larger than that for the zonal component.From the phase structures, it was found that the vertical wavelength of the diurnal variations exhibited values from 20 to 30 km for the meridional wind component, whereas for the semidiurnal oscillation they were between 50 and 70 km during equinoxes when the meridional amplitudes were stronger.

First observation of the diurnal and semidiurnal ocillation in the mesospheric winds over São João do Cariri-PB, Brazil