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 São João do 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 São João do 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 São João do Cariri leads Cachoeira Paulista. These results denote that amplitude peak at 36.5 • W and subsequently at 45 • W, compatible with a westward propagating wave.

Fast and ultrafast Kelvin wave modulations of the equatorial evening F region vertical drift and spread F development

“…Also from the MF radar over Tirunelveli, Gurubaran et al (2001) found quasi 2-day waves dominated by meridional winds occurring during December to January months. Lima et al (2004) found that the quasi 2-day waves are dominated by meridional winds at Cachoeira Paulista occurring from December to February, while at Cariri, Lima et al (2007) found that the waves occur in December to February with the same characteristics as those observed at Cachoeira Paulista, but also in June to July. From meteor radar wind measurement over Ascension Island, Pancheva et al (2004) found the overall wind characteristics to be in agreement with those of other equatorial longitudes, and the zonal wind was dominated by 3-to 7-day waves while the meridional wind component by quasi 2-day waves around southern summer months.…”

Features of 3–7-day planetary-wave-type oscillations in F-layer vertical drift and equatorial spread F observed over two low-latitude stations in China

“…In the low latitudes with the meteor radar wind measurements, quasi-2-day planetary waves in the meridional component (Lima et al, 2004) and quasi-2-day waves in the meridional component accompanied by 3-7-day waves in the zonal component (Pancheva et al, 2004) were also reported. In the middle-to-low latitudes from the simultaneous observations of two meteor radar atmospheric neutral winds, a westward-propagating quasi-2-day planetary wave was observed (Lima et al, 2007). With temperature data from TIMED-SABER (Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics; Sounding of the Atmosphere using Broadband Emission Radiometry), Pancheva et al (2009) detected planetary-scale waves from the stratosphere to the lower thermosphere during the Arctic winter of 2003-2004.…”