A numerical study of the gradient-drift instability growth rate at the fronts of the equatorial plasma bubbles

Ground and satellite measurements, as well as numerical modeling of the spatial structure of equatorial ionospheric bubbles, are carried out quite intensively. These data show that the longitude and altitude gradients of the electron density logarithm at the vertical boundaries of the bubbles can reach values of 0.001 1/m and 0.0001 1/m, respectively. With such electronic density concentration gradients, the gradient-drift instability can develop. This instability can generate ionospheric plasma irregularities with space-and-time scales are characteristic of equatorial F-spread. This article presents results of calculation of the gradient-drift instability growth rates at the ionospheric bubbles boundaries. The space-and-time structure of the equatorial plasma bubbles is obtained by numerical modeling. This simulation is based on a two-dimensional numerical model of the Rayleigh–Taylor instability in the Earth's equatorial ionosphere. This model is constructing on the condition that the Rayleigh–Taylor and gradient irregularities are strongly elongated along the magnetic field lines. The growth rates of the plasma gradient-drift instability are obtained from the dispersion equation. The results of numerical experiments confirm the possibility of generating the gradient-drift instability of ionospheric plasma. This is due to considerable longitude and altitude plasma gradients on the fronts of the developed equatorial plasma bubble. At the same time, the growth rate of the gradient-drift instability can reach values of 1/(170 s). The gradient-drift instability can be the cause of the equatorial F-spread.