INTRODUCTION TO IONOSPHERIC HEATING EXPERIMENTS AT TROMSO .2. SCIENTIFIC PROBLEMS

In the first section the theory of parametric decay instabilities (PDI) is briefly described. Then results of joint heating/incoherent scatter observations at Tromso are presented. It turns out that most of the observed features are in good agreement with that theory, while some others remain still unexplained. Among the latter features the most striking is the existence of a 'space-time blob structure', which means that the time variation of scattered power from adjacent altitudes seems to be correlated. Experiments at Arecibo often lead to results different from ours. Some scientists in the field explain these observations in terms of a 'strong turbulence' in which also caviton formation is involved. We think that most of the Tromso results can be adequately explained by the parametric decay process.