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 weakly magnetized solar wind plasma. Not only linear processes, such as wave reflection, refraction, scattering, tunneling, trapping, or mode conversion at constant frequency, are taken into account, but so are linear wave coupling, interferences between scattered waves, etc. Compact equations describing the radiation of electromagnetic waves in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">O</mml:mi> </mml:math> -, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">X</mml:mi> </mml:math> -, and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi class="MJX-tex-calligraphic" mathvariant="script">Z</mml:mi> </mml:math> -modes by the current resulting from the transformations of upper-hybrid waves on density fluctuations are determined analytically and solved numerically, providing the time variations of electromagnetic energies and the corresponding radiation rates. Jointly, on the basis of these numerical results, which validate the model’s hypotheses, analytical calculations are conducted under the framework of weak turbulence theory extended to randomly inhomogeneous plasmas, which recover the main physical conclusions stated when using the model. The dependencies of radiation rates on plasma parameters, such as magnetization, electron temperature, and 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.