Global modeling of hot O distribution in the upper thermosphere

Abstract

The existence of hot oxygen (hot O, Oh) in the upper thermosphere is mainly confirmed by optical observations of high-altitude airglow. In the experiments described here, a peak of Oh population was found at an altitude of approximately 550 km with a temperature of about 4000 K. Although it was shown that Oh concentration could reach a value of 1–2% with respect to ambient (cold) O, a realistic global distribution of Oh concentration and temperature has not been established. The presence of non-thermal atoms in the thermosphere leads to variations in the thermo-dynamical regime in the upper atmosphere. The major chemical processes involved in Oh production were taken into account in the time-dependent, Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) of the Earth in order to simulate global distribution of Oh concentration and temperature (Th). Calculations were carried out in the geomagnetic coordinate system for moderate solar, quiet geomagnetic conditions, and winter season. It was shown that the maximum Oh is located at −60° latitude, 300° longitude, and 24 UT. The Th maximum is about 2050 K. This temperature and Oh concentration cause an increase in neutral gas temperature at high thermosphere by ∼100 K during daytime and by ∼70 K during nighttime. Variations in the neutral gas velocity circulation were calculated. The maximum increase in neutral velocity was about 36 m/s, corresponding to Φ = 50°, Λ = 180° in the northern and Φ = −50°, Λ = 270° in the southern hemisphere.