Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study
Article
Article Title | Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study |
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ERA Journal ID | 1057 |
Article Category | Article |
Authors | Wexler, David B. (Author), Hollweg, Joseph V. (Author), Efimov, Anatoli I. (Author), Lukanina, Liudmila A. (Author), Coster, Anthea J. (Author), Vierinen, Juha (Author) and Jensen, Elizabeth A. (Author) |
Journal Title | The Astrophysical Journal: an international review of astronomy and astronomical physics |
Journal Citation | 871 (2), pp. 1-13 |
Article Number | 202 |
Number of Pages | 13 |
Year | 2019 |
Publisher | IOP Publishing |
Place of Publication | United States |
ISSN | 0004-637X |
1538-4357 | |
Digital Object Identifier (DOI) | https://doi.org/10.3847/1538-4357/aaf6a8 |
Web Address (URL) | https://iopscience.iop.org/article/10.3847/1538-4357/aaf6a8/ |
Abstract | Fluctuations in plasma electron density may play a role in solar coronal energy transport and the dissipation of wave energy. Transcoronal spacecraft radio sounding observations reveal frequency fluctuations (FFs) that encode the electron number density disturbances, allowing an exploration of the coronal compressive wave and advected inhomogeneity models. Primary FF observations from MESSENGER 2009 and published FF residuals from HELIOS 1975–1976 superior conjunctions were combined to produce a composite view of equatorial region FF near solar minimum over solar offset range 1.4–25R⊙. Methods to estimate the electron number density fluctuation variance from the observed FF were developed. We created a simple stacked, magnetically structured slab model that incorporated both propagating slow density waves and advected spatial density variations to explain the observed FF. Slow density waves accounted for most of the FF at low solar offset, while spatial density inhomogeneities advected at solar wind speed dominated above the sonic point at 6R⊙. Corresponding spatial scales ranged 1–38 Mm, with scales above 10 Mm contributing most to FF variance. Magnetic structuring of the model introduced radial elongation anistropy at lower solar offsets, but geometric conditions for isotropy were achieved as the slab correlation scales increased further out in the corona. The model produced agreement with the FF observations up to 12R⊙. FF analysis provides information on electron density fluctuations in the solar corona, and should take into account the background compressive slow waves and solar wind-related advection of quasi-static spatial density variations. |
Keywords | Sun: corona – Sun: oscillations – solar wind – turbulence – waves |
ANZSRC Field of Research 2020 | 510906. Space instrumentation |
510108. Solar physics | |
Byline Affiliations | Centre for Astrophysics |
University of New Hampshire, United States | |
Russian Academy of Sciences, Russia | |
Massachusetts Institute of Technology, United States | |
University of Tromso, Norway | |
Planetary Science Institute, United States | |
Institution of Origin | University of Southern Queensland |
https://research.usq.edu.au/item/q777q/spacecraft-radio-frequency-fluctuations-in-the-solar-corona-a-messenger-helios-composite-study
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