Conditions for the Kelvin‐Helmholtz Instability in the Polar Ionosphere

Abstract The Kelvin‐Helmholtz instability can be excited by a velocity shear in a fluid. Inhomogeneous flows are frequently observed in regions with polar cap patches, reversed flow events and auroral arcs, that is, regions with irregularities that disturb navigation satellite signals. Understanding the driving conditions and the evolution of the instability is therefore important. In this work, we simulate a flow shear and analyze the non‐linear instability development for a range of velocity shear strengths, shear widths and electron densities. The simulations show that Kelvin‐Helmholtz instability structures can form within 2 minutes for high‐velocity shears ( km/s) and low shear widths ( km), while auroral precipitation dampens instability development. We propose an empirical function for the relationship between instability growth and initial conditions. These results can be used to interpret observations of turbulent flow shear conditions.