Are Helium Line Intensities Affected by Abundance Variations?

Solar wind measurements show that the helium abundance in the outer solar atmosphere is not constant. Recent research has isolated some of the physical mechanisms that determine helium abundance variations along an open magnetic field line: gravitational settling in both the chromosphere and corona tends to transport helium downward, while the thermal force in the transition region and the drag force exerted by solar wind protons in the corona transport helium outward, and mixing processes work towards keeping everything in balance. The mixing efficiency is conceivably different in magnetically open and closed regions; and wind drag is missing altogether in the latter. This paper discusses if such differences might help to understand some of the features observed in the important helium lines. ed. B. Kaldeich-Schürmann,ESA-SP 446 (1999), in press