Issue A&A Volume 411, Number 3, December I 2003 Page(s) 605 - 613 Section Diffuse matter in space DOI http://dx.doi.org/10.1051/0004-6361:20031328

A&A 411, 605-613 (2003)
DOI: 10.1051/0004-6361:20031328

Dynamics of solar coronal loops

I. Condensation in cool loops and its effect on transition region lines

D. A. N. Müller¹, V. H. Hansteen² and H. Peter<sup>1

1</sup>  Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
    e-mail: peter@kis.uni-freiburg.de
²  Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern 0315, Oslo, Norway
    e-mail: Viggo.Hansteen@astro.uio.no

(Received 18 June 2003 / Accepted 22 August 2003 )

Abstract
We report numerical calculations of the condensation of plasma in short coronal loops, which have several interesting physical consequences. Firstly, we propose a connection between small, cool loops ( T < 10⁶ K), which constitute one of the basic components of the solar transition region, and prominences, in the sense that the same physical mechanism governs their dynamics: Namely the onset of instability and runaway cooling due to strong radiative losses. Secondly, we show that the temporal evolution of these loop models exhibits a cyclic pattern of chromospheric evaporation, condensation, motion of the condensation region to either side of the loop, and finally loop reheating with a period of 4000-8000 s for a loop of 10 Mm length. Thirdly, we have synthesized transition region lines from these calculations which show strong periodic intensity variations, making condensation in loops a candidate to account for observed transient brightenings of solar transition region lines. Remarkably, all these dynamic processes take place for a heating function which is constant in time and has a simple exponential height dependence.

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

Offprint request: D. A. N. Müller, dmueller@kis.uni-freiburg.de

© ESO 2003

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