A nonuniform nested grid method for simulations of RF induced ionospheric turbulence

We present a numerical scheme to simulate radio-frequency (RF) induced ionospheric turbulence, in which an electromagnetic wave is injected into the overhead ionospheric plasma. At the turning point of the ordinary mode, the electromagnetic wave undergoes linear mode-conversion to electrostatic Langmuir and upper hybrid waves that can have a much shorter wavelength than the electromagnetic wave. In order to resolve both the electromagnetic and electrostatic waves, avoiding severe restrictions on the time step due to the Courant–Friedrich–Lewy (CFL) condition, the equation of motion for the plasma particles is solved on a denser grid than that for the Maxwell equations near the mode-conversion region. An interpolation scheme is employed to calculate the electromagnetic field in the equation of motion of the plasma particles, and an averaging scheme is used to calculate the current density acting as a source in the Maxwell equation. Special care has to be taken to reduce numerical recurrence effects when the wavelength of the electrostatic wave is of the same order or shorter than the coarse grid spacing of the electromagnetic wave.