The upper atmosphere

Abstract

Wind Currents and Diffusion —The components of a uniformly mixed atmosphere kept free from winds would separate by diffusion, heavier molecules moving down and light molecules moving up. The flow of separation would be uniform at all heights; for example, in the air 1.07×10 8 molecules of helium would be expected to move up past any horizontal square centimeter per second. This upward flow of the helium would establish gravity equilibrium for helium gas above 140 km in one day, above 120 km in five days and above 106 km in fifty days. Wind‐currents, it is estimated, would cause a movement of the air above 100 km to lower altitudes once in five to twenty‐five days. Temperature of the Upper Atmosphere —Radiation and absorption coefficients lead us to expect a temperature change of approximately 140° C between day and night during the summer and 30° C during the winter, at a height of 80 km. Carbon dioxide is found to be more important than water‐vapor in determining the radiant energy which escapes from the Earth's outer atmosphere, and the conclusions are reached that the ice‐ages can be explained by slight changes in the carbon‐dioxide content of the air. Density of the Upper Atmosphere —New tables of density are compiled which show helium‐content and hydrogen‐content roughly 1/100,000 of those previously calculated for heights greater than 130 km. The conclusion is reached that above 300 km the atmosphere can not be assumed to be in a state of equilibrium, but that the percentage of very high‐energy molecules would be far higher than would be given by a Maxwellian curve for thermal equilibrium.