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SOLIS/VSM Coronal Hole Estimation Maps
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  1. SOLIS/VSM Coronal Hole Estimation Maps Carl J. Henney (NSO/SOLIS) C.J. Henney (NSO/SOLIS)

  2. KPVT Coronal Hole Maps • Daily “hand drawn” Coronal Hole images by K. Harvey and F. Recely span: 1992 to 2003 • In addition, coronal hole synoptic maps by K. Harvey and F. Recely span: 1987 to 2002 (see Harvey and Recely 2002). • Non-scanned hand drawn daily and synoptic maps back to 1974. • The “hand drawn” maps stopped with the beginning of SOLIS in September 2003. C.J. Henney (NSO/SOLIS)

  3. VSM Automated CH Maps • SOLIS-VSM began He I 1083 nm measurements in August 2003. • Daily He I 1083 nm images are publicly available (fits files will be available in fall 2006), along with automated coronal hole images and synoptic maps at: http://solis.nso.edu C.J. Henney (NSO/SOLIS)

  4. Coronal Hole Detection Recipe Following Henney & Harvey (2005): • Start with an average 1083 nm and an average magnetogram created with two consecutive observations respectively in heliographic coordinates (sine-latitude and longitude). The following images are from July 14, 2003. C.J. Henney (NSO/SOLIS)

  5. Coronal Hole Detection Recipe • Step 1: trim the East-West limb data and retain only values above 1/10 the median of positive values. C.J. Henney (NSO/SOLIS)

  6. Coronal Hole Detection Recipe • Step 1: trim the East-West limb data and retain only values above 1/10 the median of positive values. C.J. Henney (NSO/SOLIS)

  7. Coronal Hole Detection Recipe • Step 1: trim the East-West limb data and retain only values above 1/10 the median of positive values. • Step 2: spatially smooth C.J. Henney (NSO/SOLIS)

  8. Coronal Hole Detection Recipe • Step 1: trim the East-West limb data and retain only values above 1/10 the median of positive values. • Step 2: spatially smooth • Step 3: set all values above zero to a fixed value. C.J. Henney (NSO/SOLIS)

  9. Coronal Hole Detection Recipe • Step 1: trim the East-West limb data and retain only values above 1/10 the median of positive values. • Step 2: spatially smooth • Step 3: set all values above zero to a fixed value. • Step 4: smooth with the morphological image analysis function Close (e.g. Michielsen and Raedt, 2001) C.J. Henney (NSO/SOLIS)

  10. Coronal Hole Detection Recipe • Step 5: remove regions that are too small to be a coronal hole. • Step 6: use the indexes of non-zero spatial points to fill the smoothed image in step 2 with a large value (e.g. 104). C.J. Henney (NSO/SOLIS)

  11. Coronal Hole Detection Recipe • Step 5: remove regions that are too small to be a coronal hole. • Step 6: use the indexes of non-zero spatial points to fill the smoothed image in step 2 with a large value (e.g. 104). C.J. Henney (NSO/SOLIS)

  12. Coronal Hole Detection Recipe • Step 5: remove regions that are too small to be a coronal hole. • Step 6: use the indexes of non-zero spatial points to fill the smoothed image in step 2 with a large value (e.g. 104). • Step 7: smooth with the morphological image analysis function Open. C.J. Henney (NSO/SOLIS)

  13. Mean Percent Unipolarity • The cut-off levels for the percent unipolarity relative to latitude were determined using the “hand drawn” maps for the period 1992 to 2003. • The area of every coronal hole was projected into the corresponding daily average magnetic image (in heliographic coordinates). • 2,781 image pairs, with 11,241 coronal holes, were used in total. Figures from Henney & Harvey (2005) C.J. Henney (NSO/SOLIS)

  14. Coronal Hole Detection Recipe • Step 8: remove regions that are too small to be a coronal hole. • Step 9: remove regions that have a low percentage of unipolarity. • Step 10: number the coronal holes and apply sign of polarity. C.J. Henney (NSO/SOLIS)

  15. Coronal Hole Detection Comparison The auto-detection coronal hole map projected into heliocentric coordinates of the hand-drawn. C.J. Henney (NSO/SOLIS)

  16. Coronal Hole Detection Comparison An example when the two maps differed: from Malanushenko & Jones (2004) from Henney & Harvey (2005) C.J. Henney (NSO/SOLIS)

  17. Coronal Hole Detection Comparison from Malanushenko & Jones (2004) from Henney & Harvey (2005) C.J. Henney (NSO/SOLIS)

  18. Solar Wind Forecasting • The estimated area and location of coronal hole regions can be used to forecast solar wind velocities (up to 8.5 days in advance) using a simple empirical model with only a single full-disk observation (Robbins, Henney, and Harvey 2005). From Robbins, Henney, and Harvey (2005) C.J. Henney (NSO/SOLIS)

  19. Acknowledgements • The coronal hole data used here was compiled by K. Harvey and F. Recely using NSO KPVT observations under a grant from the NSF. • SOLIS VSM data used here are produced cooperatively by NSF/NSO and NASA/GSFC. • Part of this research was supported in part by the Office of Naval Research Grant N00014-91-J-1040. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. under cooperative agreement with the National Science Foundation. References Henney, C.J., & Harvey, J.W. 2005, ASP conf. Series, Vol. 346, 261. Malanushenko, O.V., & Jones, H.P. 2004, Solar Physics, Vol. 222, 43. Robbins, S. , Henney, C.J., & Harvey, J.W. 2006, Solar Physics, Vol. 233, 265. C.J. Henney (NSO/SOLIS)