Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study

Article


Wexler, David B., Hollweg, Joseph V., Efimov, Anatoli I., Lukanina, Liudmila A., Coster, Anthea J., Vierinen, Juha and Jensen, Elizabeth A.. 2019. "Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study." The Astrophysical Journal: an international review of astronomy and astronomical physics. 871 (2), pp. 1-13. https://doi.org/10.3847/1538-4357/aaf6a8
Article Title

Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study

ERA Journal ID1057
Article CategoryArticle
AuthorsWexler, 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 TitleThe Astrophysical Journal: an international review of astronomy and astronomical physics
Journal Citation871 (2), pp. 1-13
Article Number202
Number of Pages13
Year2019
PublisherIOP Publishing
Place of PublicationUnited States
ISSN0004-637X
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.

KeywordsSun: corona – Sun: oscillations – solar wind – turbulence – waves
ANZSRC Field of Research 2020510906. Space instrumentation
510108. Solar physics
Byline AffiliationsCentre 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 OriginUniversity of Southern Queensland
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