Focusing of electromagnetic beams in ionosphere with finite thermal conduction

摘要

In this communication the focusing/defocusing of (1) a single Gaussian electromagnetic beam, (2) a number of coaxial Gaussian electromagnetic beams, and (3) a Gaussian ripple on an electromagnetic beam of uniform irradiance in the ionosphere has been investigated in the paraxial approximation. The nonlinearity in the dielectric function, responsible for the focusing/defocusing arises from the redistribution of the electron density, caused by the nonuniform distribution of electron temperature, determined by the Ohmic heating of the electrons and the energy loss of electrons on account of collisions and thermal conduction. The wave frequencies have been assumed to be much larger than the electron collision frequency and the gyrofrequency. A self-consistent solution of the electromagnetic wave equation, energy balance equation (considering the solar radiation), and Fourier's equation of heat conduction has been obtained in the paraxial approximation; the available database for the midlatitude daytime ionosphere has been used for numerical computation. It is seen that as the thermal conductivity increases, the axial electron temperature and its radial gradient decrease, with the net effect that the nonlinearity in the dielectric function increases. This causes the critical curves to rise up and the two humps to get more pronounced as the thermal conduction becomes more important.