RADIATIVE HEATING OF THE SOLAR CORONA

Abstract

We investigate the effect of solar visible and infrared radiation on electrons in the Sun's atmosphere using a Monte Carlo simulation of the wave-particle interaction and conclude that sunlight provides at least 40% and possibly all of the power required to heat the corona, with the exception of dense magnetic flux loops. The simulation uses a radiation waveform comprising 100 frequency components spanning the solar blackbody spectrum. Coronal electrons are heated in a stochastic manner by low solar electromagnetic radiation. The wave coherence time and coherence for each component is determined from optical theory. The low of solar radiation allows moving electrons to gain energy from the chaotic wave field which imparts multiple random velocity kicks to these particles causing their velocity distribution to broaden or heat. Monte Carlo simulations of broadband solar radiative heating on ensembles of 1000 electrons show heating at per particle levels of 4.0 × 10–21 to 4.0 × 10–20 W, as compared with non-loop radiative loss rates of ≈1 × 10–20 W per electron. Since radiative losses comprise nearly all of the power losses in the corona, sunlight alone can explain the elevated temperatures in this region. The volume electron heating rate is proportional to density, and protons are assumed to be heated either by plasma waves or through collisions with electrons.