Observation of semiannual and annual oscillation in equatorial middle atmospheric long term temperature pattern

Extensive measurement of middle atmospheric temperature with the help of lidar data of more than 10 years (1998–2008) and TIMED/SABER data of 7 years (2002–2008), has been carried out from a low latitude station, Gadanki, India (13.5° N, 79.2° E), which exhibits the presence of semiannual oscillation (SAO) and annual oscillation (AnO). The AnO component is stronger in the mesospheric region (80–90 km) and the SAO is dominant at stratospheric altitudes (30–50 km). Overall, the AnO possesses higher amplitude ~6–7 K, and the SAO shows less amplitude ~1–2 K. The AnO present at 90 km finds crest near summer solstice, and the same at 80 km shows peak near winter solstice with a downward progression speed ~1.7 km/month. The SAO propagates downward with an average phase speed ~9 km/month and phase maximizes around equinox and solstice at 50 and 30 km, respectively. The observed SAO has also shown seasonal asymmetry in peaks