Seasonal variations in gravity wave activity at three locations in Brazil

Abstract

Abstract. Using the variance in meteor radar winds as a measure of gravity wave activity, we investigate the temporal variations in gravity waves at three locations in Brazil: São João do Cariri (2005) which makes it possible to separate the zonal and meridional components of the fluctuating wind velocity. We find that the seasonal variation of the fluctuating wind is similar to that of the amplitude of the diurnal tide, showing a predominantly semi-annual variation, stronger at Cachoeira Paulista and Santa Maria than at the quasi-equatorial station, Cariri. Both with respect to the seasonal trend and shorter term variations, strong coupling between gravity wave activity and tides is indicated by a remarkably close correlation between the fluctuating velocity and the vertical shear in the tidal winds. It is not clear as to whether this is caused by gravity wave forcing of the tides or whether it results from in situ generation of gravity waves by tidal wind shear.

Multi-year observations of gravity wave momentum fluxes at low and middle latitudes inferred by all-sky meteor radar

“…Fukuyama (1977), in his statistical study on night airglow emissions around the mesopause region, found fluctuations of 12-, 6-and 4-month periods. A study of seasonal GW activity over the three Brazilian meteor radar sites was also made by Clemesha et al (2009). In their work they analyzed the fluctuating wind velocities related to GW and observed a semiannual oscillation (SAO) in the meridional wind component over CP and SM, agreeing with our results for the variances (Fig.…”

“…Placke et al (2011b) in their analysis of GW activity over Andenes (69.3 • N, 16 • E) and Juliusruh (54.6 • N, 13.4 • E) report SAO with maxima around the solstice. As stated earlier, annual and semiannual oscillations in GW activity are anticipated and have been documented in earlier work (e.g., Antonita et al,2008;Clemesha et al, 2009;Mitchell and Beldon, 2009;Beldon and Mitchell, 2009;Senft and Gardner, 1991;Placke et al, 2011b;De Wit et al, 2014b; and references therein); however, this appears to be the first report of a 4-month oscillation in GW momentum fluxes.…”

“…We have used data from three VHF allsky interferometric meteor radars ranging from low to middle latitudes over the Brazilian sector of the Southern Hemisphere. In an earlier paper, Clemesha et al (2009) analyzed wind variances in this region but with only 1 year of data. In this paper we extend the analysis over all available data as well as studying not only wind variances but also momentum fluxes.…”

Statistics of the sodium layer parameters at low geographic latitude and its impact on adaptive-optics sodium laser guide star characteristics

“…Apart from this November minimum, the centroid height appears to exhibit a predominantly semi-annual variation, in agreement with Xiong et al (2003). A semi-annual oscillation is likely to be associated with tides and gravity waves (Clemesha et al , 2009. It is possible that the August maximum in centroid height is related to the strong meteor showers that occur in that month.…”

Mesospheric gravity wave momentum flux estimation using hybrid Doppler interferometry

“…Antonita et al, 2008;Clemesha and Batista, 2008;Mitchell, 2009, 2010;Clemesha et al, 2009;Fritts et al, 2010aFritts et al, , b, 2012aVincent et al, 2010;Placke et al, 2011aPlacke et al, , b, 2014Placke et al, , 2015Andrioli et al, 2013aAndrioli et al, , b, 2015Liu et al, 2013;de Wit et al, 2014bde Wit et al, , a, 2016Matsumoto et al, 2016;Riggin et al, 2016). This has largely arisen from a need to obtain improved spatial coverage in the parameterization of GWs and their associated momentum transport in climate models of the whole atmosphere (e.g.…”