Ana Roberta Paulino

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

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.

Lunar tides in total electron content over Brazil

Using data from Global Navigation Satellite Systems dual frequency receivers, the lunar tides were studied in the ionospheric Total Electron Content (TEC) over Brazil from 2011 to 2014. In order to calculate the amplitudes and phases of the lunar tides, quiet magnetic days within a 27-day (window) has been used to remove the solar rotation effects. Relative residuals TEC were calculated by performing a spectral analysis by removing the solar tide contributions. Lastly, a lunar month size window was used to calculate the amplitude and phase of the lunar components. Lunar diurnal tide amplitudes showed a semiannual variation with maximum in the equinox months for almost all latitudes, while, lunar semidiurnal amplitudes were larger in December and January and may be related to sudden stratospheric warming events. Both components did not display significant longitudinal variation what could be due to the short range of longitude (30 degrees). Lunar diurnal amplitudes were basically uniform over Brazil, while lunar semidiurnal amplitudes showed some peaks over the equatorial ionization anomaly crest and minimum values near the magnetic equator.