EGU General Assembly 2021
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Exploring the circular polarisation of low-frequency solar radio bursts with LOFAR and estimating the coronal magnetic field

Diana Morosan1, Anshu Kumari1, Juska Räsänen1, Emilia Kilpua1, Pietro Zucca2, Mario Bisi3, Bartosz Dabrowski4, Andrzej Krankowski4, Jasmina Magdalenić5,6, Gottfried Mann7, Hanna Rothkaehl8, and Christian Vocks7
Diana Morosan et al.
  • 1University of Helsinki, Finland (
  • 2The Netherlands Institute for Radio Astronomy, The Netherlands
  • 3United Kingdom Research and Innovation - Science and Technology Facilities Council - Rutherford Appleton Laboratory, United Kingdom
  • 4University of Warmia and Mazury, Poland
  • 5Royal Observatory of Belgium, Belgium
  • 6Katholieke Universiteit Leuven, Belgium
  • 7Leibniz--Institut für Astrophysik Potsdam (AIP), Germany
  • 8Polish Academy of Sciences, Poland

The Sun is an active star that often produces numerous bursts of electromagnetic radiation at radio wavelengths. In particular, low frequency (< 150 MHz)  radio bursts have recently been brought back to light with the advancement of novel radio interferometric arrays. However, the polarisation properties of solar radio bursts have not yet been explored in detail, especially with the Low Frequency Array (LOFAR). Here, we explore the circular polarisation of type III radio bursts and a type I noise storm and present the first Stokes V low frequency radio images of the Sun with LOFAR in tied array mode observations. We find that the degree of circular polarisation for each of the selected bursts increases with frequency for fundamental plasma emission, while this trend is either not clear or absent for harmonic plasma emission. In the case of type III bursts, we also find that the sense of circular polarisation varies with each burst, most likely due to their different propagation directions, despite all of these bursts being part of a long-lasting type III storm. Furthermore, we use the degree of circular polarisation of the harmonic emission of type III bursts to estimate the coronal magnetic field at distances of 1.4 to 4 solar radii from the centre of the Sun. We found that the magnetic field has a power law variation with a power index in the range 2.4-3.6, depending on the individual type III burst observed.

How to cite: Morosan, D., Kumari, A., Räsänen, J., Kilpua, E., Zucca, P., Bisi, M., Dabrowski, B., Krankowski, A., Magdalenić, J., Mann, G., Rothkaehl, H., and Vocks, C.: Exploring the circular polarisation of low-frequency solar radio bursts with LOFAR and estimating the coronal magnetic field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9853,, 2021.

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