Two‐dimensional simulations of gradient‐drift turbulence in the daytime equatorial electrojet

Abstract

Two‐dimensional numerical simulations of type II irregularities, attributed to gradient‐drift instabilities, are carried out with observed profiles in the daytime equatorial electrojet. Earlier work has shown that these profiles are linearly unstable to gradient‐drift modes with peak growth rates at wavelengths of the order of 1 km. The nonlinear evolution of these instabilities leads to saturated turbulent structures, with the linear drive at kilometer‐scale wavelengths quenched by a direct energy cascade to short wavelengths that are effectively damped by velocity shear and diffusion. The saturated turbulent structures show quasi‐steady 1 – 2 km horizontal waves, and appear to be quite isotropic in the plane perpendicular to the ambient magnetic field. The electron vertical velocity spectra, constructed from the simulation output, show 1–2 km vertical structures which are qualitatively in accord with recent high‐resolution radar observations at the Jicamarca Observatory in Peru.