Temperature trends in the middle atmosphere as seen by historical Russian rocket launches: Part 1, Volgograd (48.68°N, 44.35°E)
Résumé
We present a new analysis of long-term changes of temperature using data from a rocketsonde data series obtained at Volgograd (48.68°N, 44.35°E) from January 1969 to September 1995. In this series, temperature measurements exhibit discontinuities due to instrumental changes that need to be taken into account for trend estimates. Also changes of the moment when the measurements were performed can also induce discontinuities associated with the existence of atmospheric tides and bias related to solar elevation angle. Data have been selected according to the hour of the launch and sub-sets of data have been generated in order to identify homogeneous datasets. The trend analysis method used here is based on a multi-function regression analysis that assumes a linear long-term trend superimposed on natural variability. Sudden changes of the calculated mean temperature, potentially induced by discontinuities, have been estimated and taken into account by including step functions in the regression model. This analysis shows a cooling in the middle stratosphere, with magnitude increasing with altitude up to 10–15 K/decade in the upper mesosphere. The results obtained are compared with trend estimates performed earlier for other mid-latitudes data series using the same analysis. It shows a slight increase of the trend with latitude, despite the limited number of sites.