Mesospheric 2-Day waves observed simultaneously in the equatorial and low latitudes regions of Brazil

Abstract

Simultaneous observations of the atmospheric neutral winds in the mesosphere and lower thermosphere (MLT) by meteor radar have been carried out at SJodo Cariri (7.4 ◦ S, 36.5 ◦ W) and Cachoeira Paulista (22.7 ◦ S, 45.0 ◦ W). From the wind variability we investigate the atmospheric planetary-scale quasi-two-day waves, which were present at both the sites during the winter of 2004 and summer of 2004/2005. The amplitude of the meridional component was larger than that of the zonal component, reaching a maximum value of � 60 m/s at the equatorial site and � 25 m/s at the low latitude site during the winter. During the January-February period the 2-day wave was very similar at the two sites, with a maximum amplitude of � 50 m/s. The phase propagation with height shows a descending mode and upward energy propagation. The vertical wavelength estimated for Cachoeira Paulista (40-67 km) was longer than for SJodo Cariri (30-35 km), for all of the observed events. Cross-spectral analysis showed a significant coherence between the quasi-two-day oscillations observed at the two sites. From the phase difference between the two sites we concluded that SJodo Cariri leads Cachoeira Paulista. These results denote that amplitude peak at 36.5 ◦ W and subsequently at 45 ◦ W, compatible