Abstract
The ionospheric E and F regions are filled with structures that can cover cm to tens of km. Structures 10 m in size and smaller are often studied with ionospheric radars either to map the ionospheric flow or to image large scale density structures. This is often done without fully understanding how the small scale structures are generated or how their properties are affected when they grow to large amplitudes (nonlinear, or turbulent, evolution). In this talk I will quickly describe the techniques that people use to probe the irregularities, describe some important examples, and discuss some of the unresolved issues about them. In particular I will focus on how the properties evolve as the amplitude of an unstable structure grows, until it saturates and/or crashes. I will present some of the solutions that we have proposed for some "bread-and-butter" ionospheric plasma instabilities, namely: streaming instabilities (E region) and interchange instabilities (E and F region).