The Variation of the Neutral Atmospheric Properties with Local Time and Solar Activity from 100 to 10,000 km

Abstract

A semi-theoretical model of the upper atmosphere has been constructed to allow the calculation of neutral properties from 100 to 10,000 km as a function of local time and solar activity. The calculations are based on empirical density profiles obtained from a density (satelite-drag) model. Assuming diffusive equilibrium above 110 km and an isothermal region above 200 to 400 km, the remaining properties (pressure, temperature, molecular weight and constituent concentrations) are computed from a least squares procedure that, together with the hydrostatic equation and equation of state, determines individual particle concentrations. Some justification should be made for the introduction of a new model. The model greatly extends the altitude range covered by most models. In order to do this, it accounts for the variation in the rate of escape of hydrogen from the exosphere over a solar cycle. In addition, the model represents the diurnal variation of hydrogen in the exosphere, a factor previously neglected. The maximum variation in the atomic hydrogen concentration from 6000 to 10,000 km, due to both the solar activity and diurnal effects, is about a factor of four. The total variation in atomic helium is much greater; it varies by about five orders of magnitude. Finally, the diurnal and solar activity effects are enumerated in a consistent way from 100 to 200 km. Nine tables present the neutral atmospheric properties versus altitude fox sunspot maximum, average, and minimum conditions and for local times of 5 hr, 14 hr, and 21 hr (or 8 hr). These tables provide a simple format for the diurnal and solar activity variation of the properties, especially their profiles, for comparison with other models and with measurements made from rockets and satellites.