This paper presents coherent scatter radar observations of plasma irregularities in the equatorial F region ionosphere made with the JULIA (Jicamarca unattended long-term studies of the ionosphere and atmosphere) radar and discusses model equations and simulations pertinent to their interpretation. The data set shows that bottom-type and bottomside scattering layers are prevalent throughout solar minimum equinox. Bottom-type layers are undifferentiated and relatively weak layers confined to a narrow range of altitudes falling within regions of the ionosphere driven by the E region dynamo. These layers are often precursors to large-scale radar plumes as well as to bottomside layers, which are broader, more structured, and more intense layers than the bottom-type variety. Bottomside layers are the source of intermediate-scale plasma depletions that can ascend and penetrate through to the topside. Fluid simulations of the collisional interchange instability suggest that dynamo theory explains why one kind of layer emerges at a given time and altitude. ¿ 1998 American Geophysical Union