Spatio-temporal development of filaments due to the thermal self-focusing instability near the critical surface in ionospheric plasmas

A fully nonlinear spatio-temporal development of the thermal self-focusing instability of high-power radio waves in the ionosphere, near the critical surface, is the subject of the present study. These simulations improve on our earlier work by including an evolution equation for the density instead of using the assumption of constant pressure to determine the perturbed density connected with the known temperature perturbation. Using our two-dimensional nonlinear code we have investigated the time scale and associated velocity for the development of field-aligned irregularities as they spread from the critical surface both in the underdense as well as the overdense regions. The scaling of this velocity as a function of the heater electromagnetic wave radiated power (ERP) has been determined. The characteristic size of the self-focused filament as a function of ERP has also been studied. Finally, the spectrum of the density and temperature fluctuations as well as modifications in the equilibrium values of these parameters for different values of ERP is presented.