Propagation Effects in Quiet Sun Observations at Meter Wavelengths

Abstract

Quiet sun meterwave emission arises from thermal bremsstrahlung in the MK corona, and can potentially be a rich source of coronal diagnostics. On its way to the observer, it gets modified substantially due to the propagation effects - primarily refraction and scattering - through the magnetized and turbulent coronal medium, leading to the redistribution of the intensity in the image plane. By comparing the full-disk meterwave solar maps during a quiet solar period and the modelled thermal bremsstrahlung emission, we characterise these propagation effects. The solar radio maps between 100 and 240 MHz come from the Murchison Widefield Array. FORWARD package is used to simulate thermal bremsstrahlung images using the self-consistent Magnetohydrodynamic Algorithm outside a Sphere coronal model. The FORWARD model does not include propagation effects. The differences between the observed and modelled maps are interpreted to arise due to scattering and refraction. There is a good general correspondence between the predicted and observed brightness distributions, though significant differences are also observed. We find clear evidence for the presence of significant propagation effects, including anisotropic scattering. The observed radio size of the Sun is 25--30\% larger in area. The emission peak corresponding to the only visible active region shifts by 8'--11' and its size increases by 35--40\%. Our simple models suggest that the fraction of scattered flux density is always larger than a few tens of percent, and varies significantly between different regions. We estimate density inhomogeneities to be in the range 1--10\%.

References in corpus (24)

• The Murchison Widefield Array: the Square Kilometre Array Precursor at low radio frequencies
• The Murchison Widefield Array: Design Overview
• Imaging Spectroscopy of Solar Radio Burst Fine Structures
• The formation heights of coronal shocks from 2D density and Alfvén speed maps
• Anisotropic Radio-Wave Scattering and the Interpretation of Solar Radio Emission Observations
• Density Fluctuations in the Solar Wind Based on Type III Radio Bursts Observed by Parker Solar Probe
• Automated Coronal Hole Identification via Multi-Thermal Intensity Segmentation
• First Spectroscopic Imaging Observations of the Sun at Low Radio Frequencies with the Murchison Widefield Array Prototype
• Estimation of the physical parameters of a CME at high coronal heights using low frequency radio observations
• Power spectrum analysis of ionospheric fluctuations with the Murchison Widefield Array
• LOFAR observations of the quiet solar corona
• 4D Data Cubes from Radio-Interferometric Spectroscopic Snapshot Imaging
• Type III Solar Radio Burst Source Region Splitting Due to a Quasi-Separatrix Layer
• The Low-Frequency Solar Corona in Circular Polarization
• Estimating solar flux density at low radio frequencies using a sky brightness model
• Densities Probed by Coronal Type III Radio Burst Imaging
• Evidence for Super-Alfvenic oscillations in sources of Solar type III radio bursts
• First radio evidence for impulsive heating contribution to the quiet solar corona
• Unsupervised generation of high dynamic range solar images: A novel algorithm for self-calibration of interferometry data
• Wavelet-Based Characterization of Small-Scale Solar Emission Features at Low Radio Frequencies
• A weak coronal heating event associated with periodic particle acceleration episodes
• Quantifying weak non-thermal solar radio emission at low radio frequencies
• Coronal turbulence and the angular broadening of radio sources - the role of the structure function
• Constraints on coronal turbulence models from source sizes of noise storms at 327 MHz

Cited by in corpus (14)

• Imaging of the Quiet Sun in the Frequency Range of 20-80 MHz
• Imaging-spectroscopy of a band-split type II solar radio burst with the Murchison Widefield Array
• Tackling the Unique Challenges of Low-frequency Solar Polarimetry with the Square Kilometre Array Low Precursor: The Algorithm
• LOFAR observations of radio burst source sizes and scattering in the solar corona
• Detection of weak ubiquitous impulsive nonthermal emissions from the solar corona
• Insights from snapshot spectroscopic radio observations of a weak Type I noise storm
• Robust absolute solar flux density calibration for the Murchison Widefield Array
• Multiple Regions of Nonthermal Quasi-Periodic Pulsations during the Impulsive Phase of a Solar Flare
• Three-dimensional reconstruction of type U radio bursts: a novel remote sensing approach for coronal loops
• Preparing for Solar and Heliospheric Science with the SKAO: An Indian Perspective
• New Insights into Type-I Solar Noise Storms from High Angular Resolution Spectroscopic Imaging with the Upgraded Giant Metrewave Radio Telescope
• Solar Observation with MeerKAT: Demonstration of Technical Readiness and Initial Science Highlight
• Multi-diagnostic convergence: a single measurement in weakly collisional plasmas
• BIPP: An efficient HPC implementation of the Bluebild algorithm for radio astronomy