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Periodic Density Structures and the Origin of the Slow Solar WindThe source of the slow solar wind has challenged scientists for years. Periodic density structures (PDSs), observed regularly in the solar wind at 1 AU (Astronomical Unit), can be used to address this challenge. These structures have length scales of hundreds to several thousands of megameters and frequencies of tens to hundreds of minutes. Two lines of evidence indicate that PDSs are formed in the solar corona as part of the slow solar wind release and/or acceleration processes. The first is corresponding changes in compositional data in situ, and the second is PDSs observed in the inner Heliospheric Imaging data on board the Solar Terrestrial Relations Observatory (STEREO)/Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) suite. The periodic nature of these density structures is both a useful identifier as well as an important physical constraint on their origin. In this paper, we present the results of tracking periodic structures identified in the inner Heliospheric Imager in SECCHI back in time through the corresponding outer coronagraph (COR2) images. We demonstrate that the PDSs are formed around or below 2.5 solar radii-the inner edge of the COR2 field of view. We compute the occurrence rates of PDSs in 10 days of COR2 images both as a function of their periodicity and location in the solar corona, and we find that this set of PDSs occurs preferentially with a periodicity of approximately 90 minutes and occurs near streamers. Lastly, we show that their acceleration and expansion through COR2 is self-similar, thus their frequency is constant at distances beyond 2.5 solar radii.
Document ID
Document Type
Reprint (Version printed in journal)
Viall-Kepko, Nicholeen M. (NASA Goddard Space Flight Center Greenbelt, MD United States)
Vourlidas, Angelos (Johns Hopkins Univ. Laurel, MD, United States)
Date Acquired
May 5, 2016
Publication Date
July 9, 2015
Publication Information
Publication: The Astrophysical Journal
Volume: 807
Issue: 2
Subject Category
Solar Physics
Report/Patent Number
Funding Number(s)
Distribution Limits
sun: corona
sun: heliosphere
solar wind