Temperature periodicities in the mid-latitude middle atmosphere and their possible association with sunspot cycle

Abstract

Metrocket temperature (<i>T</i>) data from 580 individual soundings in the 15-80 km region over Volgograd (49°N, 44°E, station index 34560) as well as sunspot number (<i>R</i>) data during 1971-82 were used for studying the temperature periodicities in the mid-latitude middle atmosphere and their possible association with sunspot cycle. These two variables <i>T</i> and <i>R</i> formed a pair of discrete time series with length <i>N</i> = 144 and sampling interval <i>h</i> = 1 month. Using the Blackman-Turkey approach of spectrum analysis [Blackman R B &amp; Turkey J W, <i>The Measurement of Power Spectra</i>, Dower, New York, 1958], the auto- and cross-spectral estimates for 10-km steps in the 15-80 km altitude region were obtained between T and <i>R</i> as done in our earlier work [<i>Planet &amp; Space Sci</i> (<i>GB</i>), 35 (1987) 959], With the Nyqvist frequency <i>f</i>_N=0.5 cycle/month and lag variable <i>m</i> = 14 months. The estimated spectra were subjected to <i>x</i>²-test with 95% confidence level for acceptance with each harmonic fluctuation present in the spectra at 20 degrees of freedom. The presence of long-term effect of solar activity on temperature was found. The computations were carried out using CYBER 170 facility at the Vikram Sarabhai Space Centre, Trivandrum.