EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse

Aoife Maria Ryan1,2,3, Peter T. Gallagher2, Eoin P. Carley2, Michiel A. Brentjens4, Pearse C. Murphy1,2, Christian Vocks5, Diana E. Morosan6, Hamish Reid7, Jasmina Magdalenic8,9, Frank Breitling5, Pietro Zucca4, Richard Fallows4, Gottfried Mann5, Alain Kerdraon10, and Ronald Halfwerk3
Aoife Maria Ryan et al.
  • 1School of Physics, Trinity College Dublin, Dublin 2, Ireland. (
  • 2School of Cosmic Physics, Dublin Institute for Advanced Studies, D02 XF86, Ireland.
  • 3AstroTec Holding B.V., Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, Netherlands.
  • 4ASTRON, The Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands.
  • 5Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, D-14482 Potsdam, Germany.
  • 6Department of Physics, University of Helsinki, P.O. Box 64, FI-00014 Helsinki, Finland.
  • 7Department of Space and Climate Physics, University College London, London, RH5 6NT, UK.
  • 8Solar-Terrestrial Centre of Excellence—SIDC, Royal Observatory of Belgium, 3 Avenue Circulaire, B-1180 Uccle, Belgium.
  • 9Center for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, B-3001 Leuven, Belgium.
  • 10LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Universit de Paris, 5 Place Jules Janssen, 92195 Meudon, France.

The solar corona is a highly-structured plasma which can reach temperatures of more than 2 MK. At low frequencies (decimetric and metric wavelengths), scattering and refraction of electromagnetic waves are thought to considerably increase the imaged radio source sizes (up to a few arcminutes). However, exactly how source size relates to scattering due to turbulence is still subject to investigation. The theoretical predictions relating source broadening to propagation effects have not been fully confirmed by observations, due to the rarity of high spatial resolution observations of the solar corona at low frequencies. Here, the LOw Frequency ARray (LOFAR) was used to observe the solar corona at 120–180 MHz using baselines of up to 3.5 km (corresponding to a resolution of 1–2’) during the partial solar eclipse of 2015 March 20. A lunar de-occultation technique was used to achieve higher spatial resolution (0.6’) than that attainable via standard interferometric imaging (2.4’). This provides a means of studying the contribution of scattering to apparent source size broadening. This study shows that the de-occultation technique can reveal a more structured quiet corona that is not resolved from standard imaging, implying scattering may be overestimated in this region when using standard imaging techniques. However, an active region source was measured to be 4’ using both de-occultation and standard imaging. This may be explained by increased scattering of radio waves by turbulent density fluctuations in active regions, which is more severe than in the quiet Sun.

How to cite: Ryan, A. M., Gallagher, P. T., Carley, E. P., Brentjens, M. A., Murphy, P. C., Vocks, C., Morosan, D. E., Reid, H., Magdalenic, J., Breitling, F., Zucca, P., Fallows, R., Mann, G., Kerdraon, A., and Halfwerk, R.: LOFAR Imaging of the Solar Corona during the 2015 March 20 Solar Eclipse, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11094,, 2021.

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