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Definition:
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An extended region of the corona, exceptionally low in density and associated with unipolar photospheric regions having ”open” magnetic field topology. Coronal holes are largest and most stable at or near the solar poles, and are a source of high-speed solar wind. Coronal holes are visible in several wavelengths. Transequatorial coronal holes are the source of many recurrent geomagnetic disturbances since their lifetimes are months to years. The solar wind emanating from these holes is characteristically high in velocity and low in density.
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