Physical Origin of Short Scale Plasma Structures in the Auroral F Region

The E⃗×B⃗ drift instability in the auroral F region of the ionosphere is known to create long scale finger like plasma structures in the presence of a density inhomogeneity and an ambient electric field. These structures elongate mainly along the density inhomogeneity direction. In situ measurements as well as scattering experiments have also revealed the existence of small scale structures in this region. The authors propose that such structures are created due to the breakup of the long scale structures on account of their differential stretching from sheared electric fields. Using heuristic physical arguments and dimensional analysis the authors derive a general criterion for the onset of such breakups. The analytic results are validated from numerical simulations of the full set of basic nonlinear equations describing the instability and should prove useful in the prediction and interpretation of the spread F in the high latitude region. Key Points The E⃗×B⃗ drift instability in the auroral F region of the earth's ionosphere creates long scale finger like structures. These structures elongate mainly along the density inhomogeneity direction and occasionally break into small scale structures Using heuristic physical arguments and dimensional analysis The authors derive a general criterion for the onset of such breakups The criterion is validated using numerical simulations