Abstract
Abstract. We have applied a modified composite day analysis to the Hocking (2005) technique to study gravity wave (GW) momentum fluxes in the mesosphere and lower thermosphere (MLT). Wind measurements from almost continuous meteor radar observations during June 2004–December 2008 over São João do Cariri (Cariri; 7° S, 36° W), April 1999–November 2008 over Cachoeira Paulista (CP; 23° S, 45° W), and February 2005–December 2009 over Santa Maria (SM; 30° S, 54° W) were used to estimate the GW momentum fluxes and variances in the MLT region. Our analysis can provide monthly mean altitude profiles of vertical fluxes of horizontal momentum for short-period (less than 2–3 h) GWs. The averages for each month throughout the entire data series have shown different behavior for the momentum fluxes depending on latitude and component. The meridional component has almost the same behavior at the three sites, being positive (northward), for most part of the year. On the other hand, the zonal component shows different behavior at each location: it is positive for almost half the year at Cariri and SM but predominantly negative over CP. Annual variation in the GW momentum fluxes is present at all sites in the zonal component and also in SM at 89 km in the meridional component. The seasonal analysis has also shown a 4-month oscillation at 92.5 km over SM in the zonal component and over CP at the same altitudes but for the meridional component.
Highlights
It is widely accepted that atmospheric gravity waves (GWs) are responsible for the energy and momentum transport from the lower to the upper atmosphere
We have applied modified composite day (MCD) analysis to the meteor radar data from three sites located at São João do Cariri (Cariri; 7◦ S, 36◦ W), Cachoeira Paulista (CP; 23◦ S, 45◦ W) and Santa Maria (SM; 30◦ S, 54◦ W)
For the momentum fluxes, and , positive values characterize vertical transport of eastward- and northward-directed momentum and negative values characterize westward- and southward-directed momentum. Observing mainly this region we can see some similarities and some differences in the GW momentum fluxes from one year to another
Summary
It is widely accepted that atmospheric gravity waves (GWs) are responsible for the energy and momentum transport from the lower to the upper atmosphere. The deposition of this energy and momentum by wave breaking plays a crucial role in the dynamics and energy balance of the mesosphere and lower thermosphere (MLT) region In this context the Hocking (2005) technique has helped in making plenty of data sites around the world available, leading to a better understanding of the morphology of global gravity wave-induced momentum fluxes. Andrioli et al (2013a) described a method for using the technique in composite days with the purpose of maximizing the number of available meteor echoes and allowing the investigation of momentum fluxes using simple meteor radars with improved accuracy and with no contamination by tides and planetary waves This method does not allow momentum fluxes with high time resolution to be inferred, we can at least investigate the monthly mean and the seasonal variation in the fluxes without tide and planetary wave contamination. In an earlier paper, Clemesha et al (2009) analyzed
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