Propagation of ULF Waves Under Different Ionospheric Conditions

We perform a numerical study of the lateral propagation of ULF compressional Alfven waves produced by a localized source, like the HAARP facility. We consider different modes of generation modulation, including pulsed, continuous, sawtooth sweep, and sinusoidal sweep, as well as different F-layer densities. Both 2D and 3D simulations were carried out. We find that propagation is strongly dependent on F-layer density, with virtually no propagation taking place for F-layer electron number densities below 105/cm3 (foF2 < 3.0 MHz). Under conditions of robust F-layer (foF2 > 6.0 MHz) ULF waves can travel lateral distances in excess of 2000km. However, ground detection of these waves may be hampered by the "skip distance" effect; ULF waves initially travel upwards, are reflected in the upper ionosphere, and generally "skip" a horizontal distance of ~1400km before reaching the bottom of ionosphere.