Narrow Coronal Holes in Yohkoh Soft X-Ray Images and the Slow Solar Wind
AIR FORCE RESEARCH LAB HANSCOM AFB MA
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Soft X-ray images of the solar corona sometimes show narrow dark features not obviously present in HE I 10830A images. We term these narrow coronal holes NCHs. A prototype for this type of structure crossed solar central meridian on October 29, 2001. Standard source-surface models showed open magnetic field lines in this feature, tending to confirm its identification as a coronal hole. The magnetic field in this example is relatively strong above 100 G in the low-resolution Kin Peak magnetograms, and the boundaries of the open-field domain fall within the unipolar area as expected. We have surveyed the Yohkoh SXT data for other examples of this phenomenon, and have found several candidates. From observations of the associated solar wind, and from modeling, we find these regions to be sources of slow solar wind.