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Examining Periodic Solar-Wind Density Structures Observed in the SECCHI Heliospheric ImagersWe present an analysis of small-scale, periodic, solar-wind density enhancements (length scales as small as approximately equals 1000 Mm) observed in images from the Heliospheric Imager (HI) aboard STEREO-A. We discuss their possible relationship to periodic fluctuations of the proton density that have been identified at 1 AU using in-situ plasma measurements. Specifically, Viall, Kepko, and Spence examined 11 years of in-situ solar-wind density measurements at 1 AU and demonstrated that not only turbulent structures, but also nonturbulent, periodic density structures exist in the solar wind with scale sizes of hundreds to one thousand Mm. In a subsequent paper, Viall, Spence, and Kasper analyzed the alpha-to-proton solar-wind abundance ratio measured during one such event of periodic density structures, demonstrating that the plasma behavior was highly suggestive that either temporally or spatially varying coronal source plasma created those density structures. Large periodic density structures observed at 1 AU, which were generated in the corona, can be observable in coronal and heliospheric white-light images if they possess sufficiently high density contrast. Indeed, we identify such periodic density structures as they enter the HI field of view and follow them as they advect with the solar wind through the images. The smaller, periodic density structures that we identify in the images are comparable in size to the larger structures analyzed in-situ at 1 AU, yielding further evidence that periodic density enhancements are a consequence of coronal activity as the solar wind is formed.
Document ID
20110015363
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
Authors
Viall, Nicholeen M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Spence, Harlan E.
(New Hampshire Univ. Durham, NH, United States)
Vourlidas, Angelos
(Naval Research Lab. Washington, DC, United States)
Howard, Russell
(Naval Research Lab. Washington, DC, United States)
Date Acquired
August 25, 2013
Publication Date
January 1, 2010
Publication Information
Publication: Solar Physics
Publisher: Springer Science+Business Media B.V.
Volume: 267
Issue: 1
Subject Category
Solar Physics
Report/Patent Number
GSFC.JA.4754.2011
Funding Number(s)
CONTRACT_GRANT: NNG05GK65G
Distribution Limits
Public
Copyright
Other

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