Atomic hydrogen and atomic oxygen density in the mesopause region: Global and seasonal variations deduced from Solar Mesosphere Explorer near‐infrared emissions

Abstract

Atomic oxygen and atomic hydrogen have been inferred from the hydroxyl airglow measurements on Solar Mesosphere Explorer (SME) spacecraft between 0.01 and 0.0013 mbar (80–93 km). This constitutes the first measurements of the seasonal and latitudinal variations of these atomic species, in the mesopause region. At night, atomic oxygen is directly proportional to the Meinel band emission of OH. During the day the emission is proportional to the product of ozone and hydrogen. Since daytime ozone is inferred from the O2(1Δg) emission, daytime hydrogen can be inferred. Daytime atomic oxygen is then inferred from the measured hydrogen and ozone. At levels where atomic oxygen is found by both methods (at 0.0032–0.0013 mbar or 88–93 km) the day and night atomic oxygen display the same relative seasonal variations. Very large annual and semiannual changes are found in the atomic hydrogen density between 80 and 93 km. At 40°N the summer‐to‐spring ratio of atomic hydrogen exceeds a factor of 4 at 0.01 mbar (80 km). Between 80 and 90 km the odd oxygen family is found to be almost entirely atomic oxygen. Its behavior is characterized by annual variations at 40° north and south and semiannual changes at the equator; in both cases the changes are a doubling from minimum to maximum. At least part of the mid‐latitude semiannual variation in ozone is found to be due to the product of two annually varying functions. The atomic oxygen is annual and maximizes in the winter while the ozone‐oxygen partitioning, controlled mostly by temperature, maximizes in the summer due to temperature changes.