  This paper presents a study of Pc4-5 geomagnetic pulsations illustrated by
those which were observed after the sudden commencement of May 02 of 2010 at 09
: 08 UT at the Brazilian stations TTB, VSS and SMS. We carry out the spectral
analysis of a bivariate data using the Morse wavelets and calculate
polarization attributes (ellipticity ratio, tilt angle and phase difference) in
the time-frequency domain. The main pulsation wave packets occurred, for the
selected day, around noon and a small enhancement of the pulsation amplitude is
observed in the TTB station. A change in the pulsation polarization has been
found for the TTB station, which we have attributed to effects of the
equatorial electrojet.
