Long term variations in equatorial strato-and mesospheric temperatures

Abstract

M-100 Rocketsonde temperature data of Thumba in the 30 to 80 km height range for the period 1971-74 are analysed for studying the long term variations at 5 km altitude intervals. It is observed that the amplitude of the semi-annual oscillation dominates over that of the annual oscillation in the stratosphere and close to mesopause. However, the amplitude of the annual oscillation shows a quasi-peak around 70 Km altitude. The phase of the semi-annual oscillation is observed to propagate downward from mesopause while the phase of the annual component propagates on to either side from the stratopause. From a vertical time-section prepared after filtering out periods greater than 3 months wave disturbances of a few weeks period with vertical scale sizes greater than 20 Km sides are observed. A power spectral analysis shows a dominant period well, above the noise level at 52.5 days above the stratopause. Secondary peaks of lesser significance are observed with periods between 17.5 and 30.0 days.