Ionospheric irregularities

The paper describes in detail the recent experimental studies of the E and F region irregularities and also the extensive work on plasma instability theories developed to explain them. Both radio wave and spacecraft-borne experimental techniques are described in order to allow a common ground for the understanding of the data from ground-based and in situ experiments. To date, theoretical work has been mostly concentrated on the low-latitude irregularities and, together with computer simulations, has been able to explain many aspects of the experimental data. These theoretical efforts are also discussed in some detail.