AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 93. Quiet Photosphere, Chromosphere and Transition Region
Display, Thursday, June 3, 1999, 9:20am-4:00pm, Southeast Exhibit Hall

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[93.10] Velocity Redistribution as a He II 304 Intensity Enhancement Mechanism

S.D. Jordan, V. Andretta (Goddard Space Flight Center), J.W. Brosius (Ratheon ITSS), W.E. Behring (Goddard Space Flight Center), A. Garcia (Coimbra Solar Observatory)

Both Skylab and SOHO observations show that the total intensity in the He II 304Åline exceeds that predicted by standard NLTE models by at least a factor of 5. However, the NLTE models do not include the effect of flows. Carole Jordan showed that a 'velocity redistribution' of the He II ions in the presence of a sharp temperature gradient could provide the required enhancement. In earlier studies, we have reported evidence from the Goddard SERTS sounding rocket for small-scale nonthermal velocities large enough to enhance the emission by the required amount if the temperature gradient is large enough (as given by current transition region models). Here, we assess the correlation of regions of strong Sun-center quiet-Sun 304 emission observed with the CDS instrument on SOHO and the dark coarse mottles observed in the red wing of H-alpha observed at the Coimbra Solar Observatory. The significant positive correlation supports the picture of greater velocity mixing in the quiet-Sun regions producing the highest line intensity. Support for this research is provided by NASA grant 682-344-17-38 and the Coimbra Solar Observatory.

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