In search of greenhouse signals in the equatorial middle atmosphere

Abstract

A series of Rocketsonde and Radiosonde data (balloon) were collected over the equatorial station Thumba (8° N, 76° E), India extended for about two solar cycle period (1971-1993). This is one of a few longest sets of rare records available from equatorial stations. These data were now analyzed using two independent and upto date new regression models, which are based on multiple function regression theory and also takes account of successive instrumental modifications and tidal effects. These experimental results are complemented with 2-D interactive model results simulated for the same duration and found to agree well. The model accounts for the actual measured growth rate of several greenhouse gases including CO₂, CH₄, N₂O and CFCs for this period. Results of both balloon and rocket data analysis indicate a cooling of the order of 1° K /decade in the lower stratosphere which agrees well with low latitude data by other workers. A negative trend of 2 to 3°K/decade in the lower mesosphere and a rise in cooling up to 5.6° K/decade in the upper mesosphere has been observed. A loss of trend near the stratopause is noticed in annual trend analysis. However, on seasonal scales, trend structure gets modified and shows slightly stronger cooling in winter as compared to summer in the mesosphere.