Shear-modified ion-acoustic instability in ionospheric multi-ion plasmas

The linear properties of the low-frequency ion-acoustic (IA) waves are studied in a collisionless magnetoplasma using both fluid and kinetic descriptions in the presence of particle shear flows and field-aligned currents. Two different compositions of plasmas such as $\left(H^{+},,,O^{+},,,e^{-}\right)$ and $\left(H^{-},,,O^{+},,,e^{-}\right)$ are analyzed under the drift approximation and plan wave solution. Calculating a generalized linear dispersion function, shear-modified IA waves are investigated with various limiting cases. In contrast, relying on the kinetic treatment, a generalized dielectric response function is also solved to study the real frequency and growth rate of the shear-modified IA waves. Numerically, it is shown that a small concentration of negative hydrogen ions in the oxygen ionospheric plasma may lead to an increase in the growth rate and real frequency of the IA waves. The growth rate of negative hydrogen ion plasma is relatively found larger than that of positive hydrogen ion plasma. It is also noted that growth rate increases significantly with field-aligned flow of lighter species as compared with heavier ones. The magnitudes of the wave frequency and growth rate become larger when plasma species stream in the same direction as compared with counter-streaming of plasma species. Additionally, the shear flow modifies the profiles of wave instability and IA oscillations are greatly influenced by the same and opposite sides' particle shear flows. The growth rate increases as the shear flow increases, resulting in wider curves. The present findings are important for understanding the low-frequency electrostatic excitations in upper ionospheric plasma, where particle shear flows are common.