ocr: PLUME Polar plume. Plumes are best visible during activity minimum, when there are pronounced coronal holes. Polar plumes of the Sun's south pole. Top: MDI magnerogram. Middle: The million K corona as seen in the Fe IX/X emission line af 171A. Boffom: The upper chromosphere as seen in the He Il emission line at 304 A. The two lower images by EIT.
