An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations
Solar radio bursts are strongly affected by radio-wave scattering on density inhomogeneities, changing their observed time characteristics, sizes, and positions. The same turbulence causes angular broadening and scintillation of galactic and extragalactic compact radio sources observed through the s...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/acf6c1 |
| _version_ | 1797660258711109632 |
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| author | Eduard P. Kontar A. Gordon Emslie Daniel L. Clarkson Xingyao Chen Nicolina Chrysaphi Francesco Azzollini Natasha L. S. Jeffrey Mykola Gordovskyy |
| author_facet | Eduard P. Kontar A. Gordon Emslie Daniel L. Clarkson Xingyao Chen Nicolina Chrysaphi Francesco Azzollini Natasha L. S. Jeffrey Mykola Gordovskyy |
| author_sort | Eduard P. Kontar |
| collection | DOAJ |
| description | Solar radio bursts are strongly affected by radio-wave scattering on density inhomogeneities, changing their observed time characteristics, sizes, and positions. The same turbulence causes angular broadening and scintillation of galactic and extragalactic compact radio sources observed through the solar atmosphere. Using large-scale simulations of radio-wave transport, the characteristics of anisotropic density turbulence from 0.1 R _⊙ to 1 au are explored. For the first time, a profile of heliospheric density fluctuations is deduced that accounts for the properties of extrasolar radio sources, solar radio bursts, and in situ density fluctuation measurements in the solar wind at 1 au. The radial profile of the spectrum-weighted mean wavenumber of density fluctuations (a quantity proportional to the scattering rate of radio waves) is found to have a broad maximum at around (4–7) R _⊙ , where the slow solar wind becomes supersonic. The level of density fluctuations at the inner scale (which is consistent with the proton resonance scale) decreases with heliocentric distance as $\langle \delta {{n}_{i}}^{2}\rangle (r)\simeq 2\times {10}^{7}\,{\left(r/{R}_{\odot }-1\right)}^{-3.7}$ cm ^−6 . Due to scattering, the apparent positions of solar burst sources observed at frequencies between 0.1 and 300 MHz are computed to be essentially cospatial and to have comparable sizes, for both fundamental and harmonic emission. Anisotropic scattering is found to account for the shortest solar radio burst decay times observed, and the required wavenumber anisotropy is q _∥ / q _⊥ = 0.25–0.4, depending on whether fundamental or harmonic emission is involved. The deduced radio-wave scattering rate paves the way to quantify intrinsic solar radio burst characteristics. |
| first_indexed | 2024-03-11T18:27:13Z |
| format | Article |
| id | doaj.art-a889556a2a57456fb956950067ea7522 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-11T18:27:13Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-a889556a2a57456fb956950067ea75222023-10-13T16:17:14ZengIOP PublishingThe Astrophysical Journal1538-43572023-01-01956211210.3847/1538-4357/acf6c1An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio ObservationsEduard P. Kontar0https://orcid.org/0000-0002-8078-0902A. Gordon Emslie1https://orcid.org/0000-0001-8720-0723Daniel L. Clarkson2https://orcid.org/0000-0003-1967-5078Xingyao Chen3https://orcid.org/0000-0002-1810-6706Nicolina Chrysaphi4https://orcid.org/0000-0002-4389-5540Francesco Azzollini5https://orcid.org/0009-0001-7368-0938Natasha L. S. Jeffrey6https://orcid.org/0000-0001-6583-1989Mykola Gordovskyy7https://orcid.org/0000-0003-2291-4922School of Physics & Astronomy, University of Glasgow , Glasgow G12 8QQ, UKDepartment of Physics & Astronomy, Western Kentucky University , Bowling Green, KY 42101, USASchool of Physics & Astronomy, University of Glasgow , Glasgow G12 8QQ, UKSchool of Physics & Astronomy, University of Glasgow , Glasgow G12 8QQ, UKSchool of Physics & Astronomy, University of Glasgow , Glasgow G12 8QQ, UK; Sorbonne Université , École Polytechnique, Institut Polytechnique de Paris, CNRS, Laboratoire de Physique des Plasmas (LPP), 4 Place Jussieu, F-75005 Paris, FranceSchool of Physics & Astronomy, University of Glasgow , Glasgow G12 8QQ, UKDepartment of Mathematics, Northumbria University , Physics and Electrical Engineering, Newcastle upon Tyne NE1 8ST, UKDepartment of Physics, Astronomy & Mathematics, University of Hertfordshire , Hatfield AL10 9AB, UKSolar radio bursts are strongly affected by radio-wave scattering on density inhomogeneities, changing their observed time characteristics, sizes, and positions. The same turbulence causes angular broadening and scintillation of galactic and extragalactic compact radio sources observed through the solar atmosphere. Using large-scale simulations of radio-wave transport, the characteristics of anisotropic density turbulence from 0.1 R _⊙ to 1 au are explored. For the first time, a profile of heliospheric density fluctuations is deduced that accounts for the properties of extrasolar radio sources, solar radio bursts, and in situ density fluctuation measurements in the solar wind at 1 au. The radial profile of the spectrum-weighted mean wavenumber of density fluctuations (a quantity proportional to the scattering rate of radio waves) is found to have a broad maximum at around (4–7) R _⊙ , where the slow solar wind becomes supersonic. The level of density fluctuations at the inner scale (which is consistent with the proton resonance scale) decreases with heliocentric distance as $\langle \delta {{n}_{i}}^{2}\rangle (r)\simeq 2\times {10}^{7}\,{\left(r/{R}_{\odot }-1\right)}^{-3.7}$ cm ^−6 . Due to scattering, the apparent positions of solar burst sources observed at frequencies between 0.1 and 300 MHz are computed to be essentially cospatial and to have comparable sizes, for both fundamental and harmonic emission. Anisotropic scattering is found to account for the shortest solar radio burst decay times observed, and the required wavenumber anisotropy is q _∥ / q _⊥ = 0.25–0.4, depending on whether fundamental or harmonic emission is involved. The deduced radio-wave scattering rate paves the way to quantify intrinsic solar radio burst characteristics.https://doi.org/10.3847/1538-4357/acf6c1Radio burstsInterplanetary scintillationInterplanetary turbulenceSolar coronaSolar wind |
| spellingShingle | Eduard P. Kontar A. Gordon Emslie Daniel L. Clarkson Xingyao Chen Nicolina Chrysaphi Francesco Azzollini Natasha L. S. Jeffrey Mykola Gordovskyy An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations The Astrophysical Journal Radio bursts Interplanetary scintillation Interplanetary turbulence Solar corona Solar wind |
| title | An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations |
| title_full | An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations |
| title_fullStr | An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations |
| title_full_unstemmed | An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations |
| title_short | An Anisotropic Density Turbulence Model from the Sun to 1 au Derived from Radio Observations |
| title_sort | anisotropic density turbulence model from the sun to 1 au derived from radio observations |
| topic | Radio bursts Interplanetary scintillation Interplanetary turbulence Solar corona Solar wind |
| url | https://doi.org/10.3847/1538-4357/acf6c1 |
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