Automated Coronal Hole Detection Using Local Intensity Thresholding Techniques

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.

[1]  M. Velli,et al.  A Three-dimensional Model of the Solar Wind Incorporating Solar Magnetogram Observations , 2003 .

[2]  E. Roelof,et al.  A coronal hole and its identification as the source of a high velocity solar wind stream , 1973 .

[3]  M. Tokumaru,et al.  Relation between solar wind velocity and properties of its source region , 2004 .

[4]  C. J. Wolfson,et al.  The Solar Oscillations Investigation - Michelson Doppler Imager , 1995 .

[5]  Solar Polar Plume Lifetime and Coronal Hole Expansion: Determination from Long-Term Observations , 2001 .

[6]  Alyson G. Wilson.  From solar min to max: half a solar cycle with SOHO , 2002 .

[7]  J. Luhmann,et al.  Coronal Magnetic Field Context of Simple CMEs Inferred from Global Potential Field Models , 2003 .

[8]  A. Pevtsov,et al.  Large-scale Structures and their Role in Solar Activity , 2005 .

[9]  Y.-M. Wang,et al.  Characteristics of Coronal Inflows , 2002 .

[10]  Mason,et al.  Solar wind outflow and the chromospheric magnetic network , 1999, Science.

[11]  M. Guhathakurta,et al.  Solar Wind Consequences of a Coronal Hole Density Profile: Spartan 201-03 Coronagraph and Ulysses Observations from 1.15 R☉ to 4 AU , 1998 .

[12]  W. Neupert,et al.  EIT: Extreme-ultraviolet Imaging Telescope for the SOHO mission , 1995 .

[13]  J. Bookbinder,et al.  The Hinode X-Ray Telescope (XRT): Camera Design, Performance and Operations , 2008 .

[14]  S. Freeland,et al.  Data Analysis with the SolarSoft System , 1998 .

[15]  E. Antonucci,et al.  Spectroscopic measurement of the plasma electron density and outflow velocity in a polar coronal hole , 2004 .

[16]  M. Barbera,et al.  The X-Ray Telescope (XRT) for the Hinode Mission , 2007 .

[17]  C. R. DeVore,et al.  Structure and Dynamics of the Sun’s Open Magnetic Field , 2007, 0705.4430.

[18]  Shadia Rifai Habbal,et al.  Automatic Detection and Classification of Coronal Holes and Filaments Based on EUV and Magnetogram Observations of the Solar Disk , 2008 .

[19]  Multi-density model of the ionised gas in NGC 253 using radio recombination lines , 2004, astro-ph/0410676.

[20]  E. M. Reeves,et al.  An atlas of extreme-ultraviolet spectroheliograms from OSO-IV , 1970 .

[21]  Jack Ireland,et al.  Automated Boundary-extraction And Region-growing Techniques Applied To Solar Magnetograms , 2005 .

[22]  D. Mccomas,et al.  Solar Wind Scaling Law , 2003 .

[23]  Silvano Fineschi,et al.  Telescopes and Instrumentation for Solar Astrophysics , 2004 .

[24]  Alyson G. Wilson.  Fifth SOHO Workshop: The Corona and Solar Wind Near Minimum Activity , 1997 .

[25]  M. Denton,et al.  High-speed solar-wind streams and geospace interactions , 2007 .

[26]  K. L. Harvey,et al.  Polar Coronal Holes During Cycles 22 and 23 , 2002 .

[27]  Y. Pisanko.  THE POLAR SOLAR WIND: A LINEAR, FORCE-FREE FIELD, 3-D MHD MODEL , 1997 .

[28]  G. Vaiana,et al.  Atm observations, X-ray results , 1976 .

[29]  Allen S. Krieger,et al.  The structure and evolution of coronal holes , 1975 .

[30]  Saeid Belkasim,et al.  Phase-based optimal image thresholding , 2003, Digit. Signal Process..

[31]  N. Sheeley,et al.  Solar wind speed and coronal flux-tube expansion , 1990 .

[32]  H. P. Jones,et al.  Differentiating Coronal Holes from the Quiet Sun by He 1083 nm Imaging Spectroscopy , 2004 .

[33]  Properties of the quiet Sun EUV network , 1998 .

[34]  L. Xia,et al.  Links between magnetic fields and plasma flows in a coronal hole , 2005, 0801.4724.

[35]  R. H. Munro,et al.  PROPERTIES OF A CORONAL HOLE DERIVED FROM EXTREME-ULTRAVIOLET OBSERVATIONS. , 1972 .

[36]  C. Schrijver,et al.  Photospheric and heliospheric magnetic fields , 2003 .

[37]  S. Cranmer.  Coronal Holes , 2009, Living reviews in solar physics.

[38]  K. Wilhelm.  Solar coronal-hole plasma densities and temperatures , 2006 .

[39]  Peter Wurz,et al.  Development and calibration of major components for the STEREO/PLASTIC (plasma and suprathermal ion composition) instrument , 2005 .

[40]  J. Linker,et al.  The Latitudinal Excursion of Coronal Magnetic Field Lines in Response to Differential Rotation: MHD Simulations , 2006 .

[41]  Scott H. Hawley,et al.  The Magnetic Nature of Coronal Holes , 1996, Science.

[42]  F. Keenan,et al.  The Radial and Angular Variation of the Electron Density in the Solar Corona , 1999 .

[43]  M. Temmer,et al.  Periodic Appearance of Coronal Holes and the Related Variation of Solar Wind Parameters , 2007 .

[44]  D. Odstrcil.  Modeling 3-D solar wind structure , 2003 .