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

Wexler, David B. and Hollweg, Joseph V. and Efimov, Anatoli I. and Lukanina, Liudmila A. and Coster, Anthea J. and Vierinen, Juha and Jensen, Elizabeth A. (2019) Spacecraft Radio Frequency Fluctuations in the Solar Corona: A MESSENGER–HELIOS Composite Study. The Astrophysical Journal, 871 (2). pp. 1-13. ISSN 0004-637X


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.


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Item Type: Article (Commonwealth Reporting Category C)
Refereed: Yes
Item Status: Live Archive
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Faculty/School / Institute/Centre: Current - Institute for Advanced Engineering and Space Sciences - Centre for Astrophysics (1 Aug 2018 -)
Date Deposited: 05 Jul 2022 23:55
Last Modified: 07 Jul 2022 03:26
Uncontrolled Keywords: Sun: corona – Sun: oscillations – solar wind – turbulence – waves
Fields of Research (2008): 02 Physical Sciences > 0201 Astronomical and Space Sciences > 020102 Astronomical and Space Instrumentation
02 Physical Sciences > 0201 Astronomical and Space Sciences > 020109 Space and Solar Physics
Fields of Research (2020): 51 PHYSICAL SCIENCES > 5109 Space sciences > 510906 Space instrumentation
51 PHYSICAL SCIENCES > 5101 Astronomical sciences > 510108 Solar physics
Identification Number or DOI: https://doi.org/10.3847/1538-4357
URI: http://eprints.usq.edu.au/id/eprint/49406

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