Fine Structures of Solar Radio Type III Bursts and their Possible Relationship with Coronal Density Turbulence

TL;DR

This study analyzes high-resolution observations of solar radio type IIIb-III bursts, revealing fine structures that suggest coronal turbulence influences their formation, offering a new diagnostic tool for solar corona turbulence.

Contribution

It presents the first detailed analysis linking fine structures of type III bursts to coronal density turbulence, with implications for understanding solar plasma dynamics.

Findings

Density fluctuation spectral index ~ -1.7

Characteristic density perturbation scale ~ 700 km

Coronal turbulence may modulate radio burst fine structures

Abstract

Solar radio type III bursts are believed to be the most sensitive signature of near-relativistic electron beam propagation in the corona. A solar radio type IIIb-III pair burst with fine frequency structures, observed by the Low Frequency Array (LOFAR) with high temporal ($\sim10$ ms) and spectral (12.5 kHz) resolutions at 30 - 80 MHz, is presented. The observations show that the type III burst consists of many striae, which have a frequency scale of about 0.1 MHz in both the fundamental (plasma) and the harmonic (double plasma) emission. We investigate the effects of background density fluctuations based on the observation of striae structure to estimate the density perturbation in solar corona. It is found that the spectral index of the density fluctuation spectrum is about $-1.7$, and the characteristic spatial scale of the density perturbation is around $700$ km. This spectral index is very close to a Kolmogorov turbulence spectral index of $-5/3$, consistent with a turbulent cascade. This fact indicates that the coronal turbulence may play the important role of modulating the time structures of solar radio type III bursts, and the fine structure of radio type III bursts could provide a useful and unique tool to diagnose the turbulence in the solar corona.