Daily Variations of the Geomagnetic Field in the Brazilian zone
  The solar quiet daily variation (Sq) was investigated with respect to the longitudinal and seasonal variations at the Brazilian geomagnetic ground stations of Tatuoca (TTB), Vassouras (VSS ) and S\~ao Martinho da Serra (SMS). The data utilized was collected during the time interval from January to May 2010. We employed the continuous wavelet transforms and cross wavelet coherence to study the spectral content and correlations of the time series in the time-frequency domain. We identified possible phenomena of regional or global scope that could be affecting the magnetic response measured at TTB, VSS and SMS observatories. As a result some signatures of planetary waves and semidiurnal tides in the Sq variability were obtained. 
David Oliva, Marco A. Esp\'irito Santo and Andr\'es R. R. Papa
physics.space-ph