It is generally accepted that modeling Farley–Buneman instabilities require resolving ion Landau damping to reproduce experimentally observed nonlinear features. Particle in cell (PIC) simulations have been able to reproduce most of these, but at a computational cost that severely affects its scalability. This limitation hinders the study of non–local phenomena that require three dimensions or coupling with larger-scale processes. We argue that a form of the five-moment fluid system can recreate several aspects of Farley–Buneman dynamics such as density and phase speed saturation, wave turning, and heating. A comparison between the proposed fluid and a kinetic model shows good qualitative agreement.

We present an analysis of in-situ thermal ion measurements from a cusp auroral sounding rocket. Using a forward modeling procedure, we find most-probable thermal ion temperature and parallel (field-aligned) bulk flow velocity along the trajectory. Spatially and temporally intermittent fine-scale structure in upflowing/downflowing features in the dayside cusp ionosphere are presented. We show that the observed ion temperatures are consistent with Joule heating expectations if spatially and temporally intermittent drivers and responses in the dynamic cusp environment are considered. Additionally, a forward modeling procedure for the ion data interpretation is improved and a sensitivity analysis is presented.