GROWTH OF A SPIKE ON A GAUSSIAN RADIO-WAVE IN THE LOWER IONOSPHERE

A Gaussian radio wave, propagating through the ionosphere causes differential ohmic heating of electrons and subsequent quasi-linear diffusion of the plasma. The plasma duct thus formed tends to self-focus the radio wave. When the radio wave has an on-axis spike in its intensity distribution, it causes stronger local density depression and attracts more electromagnetic energy from the neighborhood, enhancing the spike. The self-focusing of the radio wave and the growth of the perturbation are coupled through the nonlinear permittivity. For RF powers corresponding to nu(o) approximately c(s) the optimum radius of the fastest growing perturbation is approximately 3c/omega(po) and the amplification length is approximately 10comega/omega(po), where nu(o) is the amplitude of electron oscillatory velocity, c(s) is the sound speed, omega is the frequency of the radio wave, and omega(po) is the plasma frequency.