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Session 5 - SOHO Corona III.
Oral session, Friday, June 27
Ballroom A, Chair: John Mariska

[5.05] Evidence in Support of the ``Nanoflare Picture'' of Coronal Heating from SUMER Data

P. Judge (HAO, NCAR), O. Wikstol, V. Hansteen (Oslo University)

We study high signal\--to\--noise profiles of \ionO4 emission lines obtained using the SUMER instrument on SoHO. Data for the quiet Sun obtained close to disk center and at the solar limb were acquired. After careful data processing in which disk data were analyzed differentially against limb data, we find a systematic correlation between a density sensitive emission line ratio and Doppler shift across the same emission line profiles.

Based upon theoretical results in an earlier paper, we argue that if wave motions are responsible for the observed behavior, then the data reveal evidence for compressive waves propagating downwards from the corona to the chromosphere. This analysis therefore lends support to the dominance of the ``nanoflare'' mechanism for coronal heating (\citeParker1988) over other theories that invoke upward wave propagation.

If instead steady flows are the cause of the observed behavior, such as return flows from spicules, then they must be such that the density is higher in the downflowing plasma. We present time series data of other transition region lines from SoHO that suggest that episodic heating such as may occur through nanoflares is a more reasonable picture of heating mechanisms than models based upon steady flows.

Program listing for Friday