Midlatitude sporadic-E layers

The starting point of this investigation is the partially transparent echo from midlatitude sporadic-E layers as recorded by ionosondes; this is the range of frequencies between the blanketing frequency and the maximum frequency. One interpretation is that it is a partial reflection at the steep gradients of electron density which characterize the vertical profile of the layers as recorded in rocket flights. The theory of reflection at gradients is developed and evaluated in the case of five layers. It is found that this mechanism is not sufficient to explain the phenomenon. An alternative explanation is that the midlatitude sporadic-E layers are not uniform in the horizontal plane but contain localized regions of high electron density. This is investigated using data obtained by incoherent-scatter radar and is found to provide a satisfactory explanation. The main features of mid latitude sporadic-E layers are consistent with the convergence of metallic ions as described by the wind-shear theory applied to gravity waves and tides. The interference of gravity waves with other gravity waves and tides can be recognized in the altitudes of occurrence and the structure of the layers. The small-scale horizontal irregularities are attributed in some cases to critical level effects and in others to fluid instabilities. The convergence of a meteor trail can, under some circumstances, account for localized enhancement of the electron density in the layer.U of I OnlyThesi