The Wind‐Shear Theory of Temperate Zone Sporadic <i>E</i>

Abstract

The assumptions on which the wind‐shear theory of temperate zone sporadic E is based are outlined and the formulation of the theory is described for the cases in which a single ion and many ions, both positive and negative, are present. Among the implications of the theory which agree with observations are that a zone of reduced occurrence of this type of sporadic E should occur at the geomagnetic dip equator, and elsewhere the occurrence should be roughly correlated with the horizontal component of the geomagnetic field. It is pointed out that horizontal electric polarization fields and vertical motion of the wind profile can affect the formation of layers, thus leading to difficulties in the interpretation of observations of winds and electron density profiles. The effect of the presence of many types of ion is discussed, and it is shown that if all the ions are positive, then the maximum electron density attained in a layer is determined by the ion with the smallest recombination coefficient, while the electron density outside the layer is much less depleted than it would be in the single‐ion case. Meteoritic ions in particular must react strongly to the presence of wind shears, and these may play an important part in the formation of sporadic E layers, especially at night. The effect of negative ions is also considered, and it is shown that these can lead to the formation of layers of positive ion density at apparently anomalous positions under suitable conditions.