Solar Physics

, Volume 256, Issue 1–2, pp 87–100

Automated Coronal Hole Detection Using Local Intensity Thresholding Techniques

STEREO SCIENCE RESULTS AT SOLAR MINIMUM

DOI: 10.1007/s11207-009-9357-2

Cite this article as:
Krista, L.D. & Gallagher, P.T. Sol Phys (2009) 256: 87. doi:10.1007/s11207-009-9357-2

Abstract

We identify coronal holes using a histogram-based intensity thresholding technique and compare their properties to fast solar wind streams at three different points in the heliosphere. The thresholding technique was tested on EUV and X-ray images obtained using instruments onboard STEREO, SOHO and Hinode. The full-disk images were transformed into Lambert equal-area projection maps and partitioned into a series of overlapping sub-images from which local histograms were extracted. The histograms were used to determine the threshold for the low intensity regions, which were then classified as coronal holes or filaments using magnetograms from the SOHO/MDI. For all three instruments, the local thresholding algorithm was found to successfully determine coronal hole boundaries in a consistent manner. Coronal hole properties extracted using the segmentation algorithm were then compared with in situ measurements of the solar wind at ∼ 1 AU from ACE and STEREO. Our results indicate that flux tubes rooted in coronal holes expand super-radially within 1 AU and that larger (smaller) coronal holes result in longer (shorter) duration high-speed solar wind streams.

Keywords

Sun: coronal holes Automated detection Sun: magnetic fields Sun: solar wind, disturbances 

Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  1. 1.Astrophysics Research Group, School of PhysicsTrinity College DublinDublin 2Ireland

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