Low Latitude Mesospheric Molecular Oxygen Profiles from Lyman-Alpha Absorption Measurements from Thumba

Abstract

Abstract The results from five rocket-borne Lyman alpha absorption measurements made at Thumba (8° 31'N, 76° 52'E) are used to study the molecular oxygen profiles of the low latitude mesosphere. The observations indicate some departures from the CIRA 72 atmospheric model. We discuss here five measurements of molecular oxygen concentrations in the 65-85 km altitude region over the low latitude rocket launching station at Thumba (8° 31'N, 76° 52'E) derived frori measurements of the absorption of solar hydrogen Lyman alpha (1216A°) in the upper atmosphere. The technique is fairly standard and the instrumentation used at Thumba has been described earlier [1]. Some of the early results have been published [2], 3 . A collection of three profiles (Fig. 1), all obtained around noon but on different occasions, showed that the measurements were in agreement to within 20%. A second order polynomial fit to the observations meets the appropriate CIRA model at 82.5 km. Below this altitude the measured molecular oxygen densities are smaller than the model values. The scale heights and the computed temperatures exceed the model atmosphere values by 30 to 50% [4].