Solar wind density turbulence and solar flare electron transport from the Sun to the Earth

TL;DR

This study models how solar flare electron beams interact with interplanetary turbulence, affecting plasma wave generation and resulting in observable electron spectra near Earth, highlighting the influence of turbulence on space weather phenomena.

Contribution

It introduces a self-consistent simulation of electron beam propagation accounting for plasma wave interactions and density fluctuations, revealing turbulence's impact on electron spectra at 1 AU.

Findings

Higher turbulence levels increase the spectral index of electron beams.

Density fluctuations suppress plasma wave growth, altering electron transport.

The electron spectrum below the break energy correlates with turbulence intensity.

Abstract

Solar flare accelerated electron beams propagating away from the Sun can interact with the turbulent interplanetary media, producing plasma waves and type III radio emission. These electron beams are detected near the Earth with a double power-law energy spectrum. We simulate electron beam propagation from the Sun to the Earth in the weak turbulent regime taking into account the self-consistent generation of plasma waves and subsequent wave interaction with density fluctuations from low frequency MHD turbulence. The rate at which plasma waves are induced by an unstable electron beam is reduced by background density fluctuations, most acutely when fluctuations have large amplitudes or small wavelengths. This suppression of plasma waves alters the wave distribution which changes the electron beam transport. Assuming a 5/3 Kolmogorov-type power density spectrum of fluctuations often observed near the Earth, we investigate the corresponding energy spectrum of the electron beam after it has propagated 1 AU. We find a direct correlation between the spectrum of the double power-law below the break energy and the turbulent intensity of the background plasma. For an initial spectral index of 3.5, we find a range of spectra below the break energy between 1.6-2.1, with higher levels of turbulence corresponding to higher spectral indices.