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Fading Coronal Structure and the Onset of Turbulence in the Young Solar WindAbove the top of the solar corona, the young, slow solar wind transitions from low-beta, magnetically structured flow dominated by radial structures to high-beta, less structured flow dominated by hydrodynamics. This transition, long inferred via theory, is readily apparent in the sky region close to 10deg from the Sun in processed, background-subtracted solar wind images. We present image sequences collected by the inner Heliospheric Imager instrument on board the Solar-Terrestrial Relations Observatory (STEREO/HI1) in 2008 December, covering apparent distances from approximately 4deg to 24deg from the center of the Sun and spanning this transition in the large-scale morphology of the wind. We describe the observation and novel techniques to extract evolving image structure from the images, and we use those data and techniques to present and quantify the clear textural shift in the apparent structure of the corona and solar wind in this altitude range. We demonstrate that the change in apparent texture is due both to anomalous fading of the radial striae that characterize the corona and to anomalous relative brightening of locally dense puffs of solar wind that we term "flocculae." We show that these phenomena are inconsistent with smooth radial flow, but consistent with the onset of hydrodynamic or magnetohydrodynamic instabilities leading to a turbulent cascade in the young solar wind.
Document ID
20170003238
Document Type
Reprint (Version printed in journal)
Authors
DeForest, C. E. (Southwest Research Inst. Boulder, CO, United States)
Matthaeus, W. H. (Delaware Univ. Newark, DE, United States)
Viall, N. M. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Cranmer, S. R. (Colorado Univ. Boulder, CO, United States)
Date Acquired
April 7, 2017
Publication Date
September 1, 2016
Publication Information
Publication: The Astrophysical Journal
Volume: 828
Issue: 2
ISSN: 0004-637X
Subject Category
Solar Physics
Report/Patent Number
GSFC-E-DAA-TN40883
Distribution Limits
Public
Copyright
Other