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Metric and decametric radio-emissions from the Sun are the only direct sourceof information about the dynamics of non-thermal electrons in the upper corona.In addition, the combination of spectral and imaging (sizes, shapes, andpositions) observations of low-frequency radio sources can be used as a uniquediagnostic tool to probe plasma turbulence in the solar corona and innerheliosphere. The geometry of the low-frequency sources and its variation withfrequency are still not understood, primarily due to the relatively low spatialresolution available for solar observations. Here we report the first detailedmulti-frequency analysis of the sizes of solar radio sources observed by theLow-Frequency Array (LOFAR). Furthermore, we investigate the source shapes byapproximating the derived intensity distributions using 2D Gaussian profileswith elliptical half-maximum contours. These measurements have been madepossible by a novel empirical method for evaluating the instrumental andionospheric effects on radio maps based on known source observations. Theobtained deconvolved sizes of the sources are found to be smaller than previousestimations, and often show higher ellipticity. The sizes and ellipticities ofthe sources inferred using 2D Gaussian approximation, and their variation withfrequency are consistent with models of anisotropic radio-wave scattering inthe solar corona.

Sizes and shapes of sources in solar metric radio bursts