The<i>F</i>-region seasonal anomaly

Abstract

It is shown that in the morning hours the ionospheric F region at low midlatitudes does not show a seasonal anomaly, and that its behavior versus the solar zenith angle is identical with that in the winter at higher iatitudes. A departure from this law develops progressively with increasing latitude in the summer season. Mechanisms are presented that could reduce the summer electron content whereas it is difficult to find a sensible process that could markedly enhance the winter values.