SporadicEand the wind structure of theEregion

Abstract

Observations of neutral winds from visible trails of gun‐launched vehicles and radio soundings of the ionospheric sporadic E layers are described and compared. It is shown that the wind structure accounts for many features of the sporadic E layer variation on two nights of observation, through the vertical ion convergence mechanism described most recently by MacLeod [1966]. Except for some transient disagreements, the sporadic E is found to accompany the height variation of certain levels of zero ion velocity induced by the neutral wind. The peak electron number density of the layers diminishes when the wind structure leads to ion divergence at the sporadic E height, and the density is observed to increase when the ion velocity permits the descent of ‘new’ ionization from above. New layers ‘arrive’ at night in accord with the observed development and descent of new nodes of ion convergence. The daytime evolution of a principal sporadic E layer is described and related to its subsequent nighttime association with the wind structure. Together with other published evidence that similar layers consist of long‐lived monatomic ions ultimately from meteoric influx, it is concluded that the neutral wind serves as a scavenger of this material that would otherwise accumulate to a far higher ionic concentration in the upper atmosphere.

Some current developments in radio systems for sounding ionospheric structure and motions

“…All three components of motion (x, y, z) interpreted as a background wind, will contribute through interaction with the inclined geomagnetic field to a vertical component of ion motion, V z . If the ionization flux due to V z converges at some altitude, a sporadic E-layer may form there in accord with recently developed theories of sporadic E [18], [19]. This is found to be the case in the present example.…”

Vertical movement of temperate-zone sporadicElayers

“…To date the wind-shear theory has been considered mainly in terms of quasi-steady conditions in which the wind profile does not vary with time. Observations of neutral winds, however, suggest that the profile of horizontal velocities descends with time [Revah and Spizzichino, 1966;Rosenburg and Justus, 1966;Wright et al, 1967]. This is consistent with the theory of internal gravity waves [Hines, 1960], which predicts that the phase velocity of the x Present address: Department of Physics, University of Toronto, Toronto 5, Canada.…”

“…The Whitehead-Storey theory of sporadic E formation through the wind-shear mechanism has been developed in considerable detail [e.g., see Whitehead, 1967; Ax•ord, l!J67] and found to account for much of the observed data [Wright et al, 1967;Aubry et al, 1966;MacLeod, 1966;Young et al, 1967]. However, it is commonly found that low-altitude (85-95 km) sporadic E layers occur at positions that do not have any clear relationship to simultaneously observed neutral wind profiles [Wright et al, 1967;Aubry et al, 1966;Mac-Leod, 1966], and indeed the layers often appear to be located in regions of ionization divergence, in direct contradiction to the usual predictions of the wind-shear theory.…”

Height and critical frequency variations of the sporadic-E layer at midlatitudes

“…It is well established that the wind shear mechanism plays a major role in sporadic E layer formation (Whitehead, 1961(Whitehead, , 1989. According to this theory the sporadic E layer is created by the vertical compression of metal ions in a shear of the horizontal wind (Wright et al, 1967). Wind shears are provided by tidal waves producing a descending layer.…”