Vertical movement of temperate-zone sporadicElayers

The wind-shear theory of the formation of temperate-zone sporadic E layers is extended to take into account effects associated with a neutral wind profile having a descending phase velocity. It is shown that layers of long-lived ions (presumably of meteoritic origin) that are formed at higher altitudes are carried down with the wind profile to a region roughly 85–95 km in altitude, where they are dumped. Above about 95-km altitude the layers are trapped in portions of the neutral wind profile having a shear of the correct sign according to the simple (equilibrium) form of the wind-shear theory. Below about 95 km the layers are not trapped in this manner, and their position shows no obvious correlation with the sign of the neutral wind shear. The effects of diffusion are discussed, and an expression for the equilibrium width of a sporadic E layer is obtained.