Equatorial ionosphere Rayleigh-Taylor instability in the presence of double-ion species

Plasma Rayleigh-Taylor instability plays a crucial role in the development of irregularities in the nocturnal equatorial ionosphere. In traditional theories, only the dominant element O⁺ is taken into consideration. As a result, the liner equation is independent with the ion mass and density. In fact, in some cases, there are not only one kind of positive ion in the F region of the ionosphere, such as in dusty plasma or in the ionospheric disturbances resulting from artificially chemical releases. It is essential to understand the effect of molecular ions in the collisional Rayleigh-Taylor instability. In this paper, a linear perturbation analysis associated with continuity equations, momentum equations and current conservation equation has been used to obtain a growth rate expression in the presence of double-ion species. The new expression reveals that the growth rate is dependent with the number densities and masses of both the ion elements, and especially, the proportions of the two kinds of ions contribute to growth rate.