Numerical modelling of a metallic ion sporadic-E layer

A one-dimensional time-dependent model of the ionosphere has been developed and applied to the study of a metallic ion sporadic-E layer observed in the Aladdin 1 experiment carried out at Eglin AFB, Florida, 20 November 1970. The model develops the molecular ion background ionosphere using a dynamic photochemical calculation from noon to a time near model sunset. A representative metallic ion altitude profile is then introduced, the divergence terms included in the continuity equations, and the integration carried forward. Introducing an ad hoc constant electric field of 2 mv m⁻¹ directed to the south, the model metallic ion sporadic-E layer forms at the proper altitude and reaches the measured peak density in about a half hour. Changing the initial metallic ion profile changes the time to reach peak density and the degree of asymmetry of the layer, but the layer altitude is determined asymptotically by the location of the convergent node of the vertical ion velocity profile. The background ionospheric density calculated with the model agrees within experimental error with the experimental profile. The calculations support the hypothesis that midlatitude sporadic-E layers are caused by neutral-wind-induced compression of metallic ions resulting from meteoric ablation in the lower E region.