Astron. Astrophys. 357, 743-756 (2000)

SUMER observations of transition region fine structures

E. Landi ^1,2, H.E. Mason ³, P. Lemaire ⁴ and M. Landini <sup>2

1</sup> Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany
² Dipartimento di Astronomia e Scienza dello Spazio, Università di Firenze, Italia
³ Department of Applied Mathematics and Theoretical Physics, Silver Street, Cambridge CB3 9EW, UK
⁴ Institut d'Astrophysique Spatiale, Unité Mixte CNRS - Université de Paris XI, Bat 121, 91405 Orsay, France

Received 16 November 1999 / Accepted 24 March 2000

Abstract

The SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument on SOHO (Solar and Heliospheric Observatory) provides an opportunity to observe and study the solar transition region with high spatial and spectral resolution. We present new evidence to confirm that the emission from the quiet Sun at  K is dominated by cool loop-like fine structures which cluster across the chromospheric network boundaries. The electron density of these structures is found to be around  cm^-3. The red-shifts in spectral line profiles and the non-thermal widths from lines formed at this temperature are found to be correlated with intensity. The properties of explosive events with irregular profiles are explored. A large jet-like structure is analysed. The results of our analysis are compared with recent predictions from numerical models.

Key words: Sun: corona Sun: transition region Sun: UV radiation

Send offprint requests to: E.Landi (enricol@arcetri.astro.it)

© European Southern Observatory (ESO) 2000

Online publication: June 5, 2000

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