Growth of plasma waves of scales longer than 10 km by gradient-drift instability in the E-region of equatorial ionosphere

In this study, a linear analysis of the Gradient Drift Instability (GDI) applicable for horizontal wavelengths longer than 10 km in the E region is presented. By analytically solving the non-local differential equation for the polarization potential, analytical forms of the dispersion relation and growth rate, hosting new contributions from non-local effects, are obtained. The new growth rate and the amplitude of polarization potential are examined for a wide range of wavelengths that reveal the positive growth of GDI for wavelengths of ∼25 km. These characteristics raise the possibility of the formation of unstable structures of vertical size ∼20–30 km in the upper E region, often observed during twilight hours.