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

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 ($\sim 10$ 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.

7 pages (text), 5 figures, Submitted to ApJ

References in corpus (6)

• Imaging Spectroscopy of Solar Radio Burst Fine Structures
• LOFAR tied-array imaging of Type III solar radio bursts
• Dynamics of electron beams in the solar corona plasma with density fluctuations
• Large scale simulations of solar type III radio bursts: flux density, drift rate, duration and bandwidth
• Imaging Spectroscopy of Type U and J Solar Radio Bursts with LOFAR
• Solar plasma radio emission in the presence of imbalanced turbulence of kinetic-scale Alfvén waves

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