ADVANCES IN IONOSPHERIC PHYSICS - ROLES, RELEVANCE AND PREDICTIONS IN THE SYSTEM OF SOLAR-TERRESTRIAL PLASMAS

The ionosphere can be viewed as the culmination of all coupling processes in the system of solar‐terrestrial plasmas, including such diverse phenomena as coronal mass ejections, magnetospherically‐imposed electric fields, and solar‐driven thermospheric tides. It follows therefore that the accurate and self‐consistent specification of ionospheric plasma distributions represents a critical test of our understanding of the ionosphere itself and the myriad of controls and coupling mechanisms from the Sun to the Earth. There is, however, neither a code nor a model that can accurately specify the quiet‐ or storm‐time characteristics of ionospheric plasma distributions. Nor is there an adequate database to constrain the models and enforce unique quantitative solutions. Among the challenges are the ionospheric structures themselves which span eight orders of magnitude in size. Their theoretical and experimental investigation requires a broad computational grid and unique combinations of “in situ” and remote sensing techniques to define the hierarchy of sizes and cause‐effect terms. These structures range from tens‐of‐thousands of kilometers to tens‐of‐centimeters, with scale lengths that can be horizontal or vertical in the Earth's gravitational field, or parallel or perpendicular to the geomagnetic field depending on the causal mechanisms. Copyright 1995 by the American Geophysical Union.