IONOSPHERIC SMALL-SCALE STRUCTURES AND TURBULENCE INFERRED FROM EISCAT OBSERVATIONS - A REVIEW

Measurements of the European incoherent scatter facility (EISCAT) occa sionally indicate the presence for brief periods of ionospheric small- scale structures and turbulence at scales smaller than the typical spa ce and time resolution of the radar. Such events violate the assumptio n of space and time uniformity used in the analysis of the received si gnal. This results in an erroneous estimate of the derived ionospheric parameters, or even in the failure of the analysis when the measured spectrum departs too much from its usual shape. We review recently pub lished observations from EISCAT data of two types of such phenomena, n amely the small-scale auroral structures of intense flow bursts, and t he ion-acoustic turbulence. The large differences in their spectral si gnature and origin illustrate both the variety of the small-scale phen omena occuring in the ionosphere, and the capability of the incoherent scattering technique to detect them and to infer original information s on the mechanisms responsible for them.