Linear mode conversion theory of radio emission from turbulent solar wind plasmas

Abstract

This work presents a new theoretical and numerical model describing all possible linear interactions between upper-hybrid wave turbulence and random density fluctuations in a solar wind plasma; not only linear processes as wave reflection, refraction, scattering, tunneling, trapping, or mode conversion at constant frequency are taken into account, but also linear wave coupling, interferences between scattered waves, etc. Compact equations describing the time evolution of electromagnetic fields radiated in the $\mathcal{O}$, $\mathcal{X}$ and $\mathcal{Z}$ modes by the current due to transformations of upper-hybrid waves on density fluctuations, as well as the dispersion and polarization properties of the modes, are determined analytically and solved numerically, providing the time variations of electromagnetic energies and corresponding radiation rates. Jointly, on the basis of these numerical results that validate theoretical hypotheses, analytical calculations are conducted in the framework of weak turbulence theory extended to randomly inhomogeneous plasmas, that recover the main physical conclusions stated using the new model. The dependencies of radiation rates on plasma parameters as the magnetization, the electron thermal velocity and the average level of random density fluctuations are determined in the form of scaling laws. This work opens a new way to analyze the efficiency of electromagnetic emissions at plasma frequency by realistic wave and density turbulence spectra interacting in solar wind plasmas.