Production and prediction of sporadic E

This is a survey of the experimental observations and theories of formation of all types of sporadic E. The wind‐shear theory is most likely to explain temperate‐zone sporadic E. In the equatorial zone, VHF reflections are most probably due to the two‐stream plasma instability, though gradient instabilities may play a part in producing the irregularities that cause HF vertical‐incidence reflection. In the auroral zone, energetic particles dumped by any one of a variety of mechanisms cause ionization. This ionization has to be moved into thin layers of irregularities to cause auroral sporadic E and radio aurora reflections. Many recommendations are made to further the understanding of and the prediction of sporadic E for communication purposes.