This paper reviews the state of ionospheric predictions following the Solar-Terrestrial Predictions Workshop held in April 1979 at Boulder. The review includes: the various uses of the ionosphere, the physical bases, long-term and short-term variations, the techniques used for their prediction, and the current state-of-the-art of ionospheric predictions. The different requirements of various users (system designers and planners) are discussed together with the needs for timely dissemination systems. Because ionospheric predictions and forecasts have been underway for many years, the advances have been of second order. The main advances include the incorporation of features such as the auroral oval, the magnetospheric cleft, the mid-latitude trough, etc, the positions of which vary with local time and solar-terrestrial activity. Other advances include: four-dimensional models of the ionosphere, which yield electron density profiles useful in ray tracing; some new methods for predicting E layer and Es layer characteristics; transionospheric propagation, which requires prediction of total electron content; and scintillation characteristics. In recent years, advances have been made in the use of empirical and physical models of the ionosphere. Short-term ionospheric forecasting has also progressed in recent years primarily through technological advances in data acquisition (e.g., satellite sensors), data processing (computers), and dissemination of information. Nevertheless, solar-flare forecasting—a vital ingredient of magnetic/ionospheric storm forecasting—is still largely an art in which the forecasters' experience and skill, in recognizing and interpreting solar features, play the dominant role.
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