AURORAL ELECTROJET PLASMA IRREGULARITY THEORY AND EXPERIMENT - A CRITICAL-REVIEW OF PRESENT UNDERSTANDING AND FUTURE-DIRECTIONS

We review the experimental observations of meter scale plasma irregula rities in the auroral E region and the status of their theoretical und erstanding. Most of the experimental data is derived from VHF radar sc atter experiments, but sounding rockets also provide crucial informati on not obtainable from radars. Linear theories correctly predict the a ltitude of occurence, strong magnetic aspect sensitivity, marginal ins tability, and typical phase velocities. Subsequent nonlinear theories have been developed to account for other observed features but with le ss satisfying application. Further understanding of amoral electrojet irregularities is impeded by precision limitations of existing instrum ents, by radar data which may seem incompatible, by the usually poor k nowledge of the ambient conditions during these experiments, and by so me confusion in the nomenclature (e.g. ''type 2'') used to describe th e irregularities. We hope to clarify some of these experimental and th eoretical issues. We will discuss observational ''facts'' that need to he refined and point out weaknesses of existing theories or their com mon interpretations. Finally, we will outline some avenues for future experimental and theoretical pursuit.