Fine structures of solar radio bursts: origins and radio-wave propagation effects

Chrysaphi, Nicolina (2021) Fine structures of solar radio bursts: origins and radio-wave propagation effects. PhD thesis, University of Glasgow.

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Abstract

Solar eruptive events are associated with radio emissions that appear as impulsive increases in intensity, known as solar radio bursts. Turbulence in the solar corona impacts the propagation of radio waves, obscuring the intrinsic emission properties. Here, anisotropic scattering on small-scale density fluctuations is investigated using novel 3D radio-wave propagation simulations. Several observed radio properties are simultaneously reproduced for the first time, verifying the necessity to consider anisotropic scattering. The sub-second evolution of fine radio burst properties at a single frequency is also investigated, enabled by conducting observations that utilise the unprecedented imaging capabilities of the LOw-Frequency ARray (LOFAR). The fundamental and harmonic sources of a Type IIIb burst are quantitatively compared, demonstrating that harmonic emissions arise from an intrinsic source with a finite size and finite emission duration. Drift-pair burst observations are successfully described by the radio echo hypothesis. It is shown that the radio echo, which produces the second Drift-pair component, is detected only when the anisotropy is strong. A dependence of the observed properties on the source's intrinsic location and on the assumed emission-to-plasma frequency ratio is inferred. Moreover, the subbands of a split-band Type II burst are simultaneously imaged for the first time. Despite the large separations observed between subband sources, it is shown that once scattering is quantitatively accounted for, the sources become co-spatial. Corrections on the observed source locations also allude to lower coronal densities. Additionally, the first observation of a Type II burst that transitions between a stationary and drifting state—termed as a transitioning Type II burst—is reported. The radio emissions are related to a jet eruption that drives a streamer-puff CME. Overall, state-of-the-art simulations and radio observations are combined and compared. The importance of accounting for radio-wave propagation effects—primarily anisotropic scattering—and the consequence of neglecting to do so on any subsequent interpretations is illustrated.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Solar physics, solar radio bursts, radio-wave propagation simulations, radio-wave scattering, coronal mass ejection shocks, imaging spectroscopy, LOFAR.
Subjects: Q Science > Q Science (General)
Q Science > QB Astronomy
Q Science > QC Physics
Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
Supervisor's Name: Kontar, Prof. Eduard P.
Date of Award: 2021
Depositing User: Dr Nicolina Chrysaphi
Unique ID: glathesis:2021-82010
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 17 Feb 2021 07:49
Last Modified: 23 Feb 2021 14:16
Thesis DOI: 10.5525/gla.thesis.82010
URI: http://theses.gla.ac.uk/id/eprint/82010

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