Equatorial spread F modeling: Multiple bifurcated structures, secondary instabilities, large density ‘bite-outs,’ and supersonic flows

Abstract

The Naval Research Laboratory has recently developed a new two‐dimensional code to study equatorial spread F (ESF): NRLESF2. The code uses an 8th order spatial interpolation scheme and the partial donor cell method. This allows the model to capture very sharp gradients over ∼ 4 grid cells and to assess the impact of numerical diffusion on the dynamics of ‘bubble’ evolution. Simulation results are presented that show new and complex ESF bubble dynamics: multiple bifurcations, secondary instabilities, density ‘bite‐outs’ of over three orders of magnitude, and supersonic flows within low density channels (V ≃ few km/s). These results are consistent with radar and satellite observations, as well as optical images. It is also shown that numerical diffusion can inhibit bubble bifurcation and the development of small‐scale structure.