A report on long-term trends and variabilities in middle atmospheric temperature over Gadanki (13.5 super(o)N, 79.2 super(o)E)

The present study reports long-term variabilities and trends in the middle atmospheric temperature (March 1998-2008) derived from Rayleigh backscattered signals received by the Nd:YAG lidar system at Gadanki (13.5 super(o)N, 79.2 super(o)E). The monthly mean temperature compositely averaged for the years 1998-2008 shows maximum temperature of 270K in the months of March-April and September at altitudes between ~45 and 55km. The altitude profile of trend coefficients estimated from the 10 years of temperature observations using regression analysis shows that there exists cooling at the rate with 1 sigma uncertainty of 0.12+/-0.1K/year in the lower stratospheric altitudes (35-42km) and 0.2+/-0.08K/year at altitudes near 55-60km. The trend is nearly zero (no significant cooling or warming) at altitudes 40-55km. The regression analysis reveals the significant ENSO response in the lower stratosphere (1K /SOI) and also in mesosphere (0.6K/SOI). The solar cycle response shows negative maxima of arrow right .5K/100F10.7 units at altitudes 36km, 41km and 1K/100F10.7 units at 57km. The response is positive at mesospheric altitude near 67km (1.3K/100F10.7 units). The amplitudes and phases of semiannual, annual and quasi-biennial oscillations are estimated using least squares method. The semiannual oscillation shows larger amplitudes at altitudes near 35, 45, 62 and 74km whereas the annual oscillation peaks at 70km. The quasi-biennial oscillations show larger amplitudes below 35km and above 70km. The phase profiles of semiannual and annual oscillations show downward propagation.