Astron. Astrophys. 351, 721-732 (1999)

Modelling explosive events in the solar atmosphere

L.M. Sarro ¹, R. Erdélyi ², J.G. Doyle ³ and M.E. Pérez <sup>3

1</sup> Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF) INTA, P.O. Box 50727, 28080 Madrid, Spain (lsb@laeff.esa.es)
² Department of Applied Mathematics, University of Sheffield, Hicks Building, Western Bank, S3 7RH, England, UK (Robertus@sheffield.ac.uk)
³ Armagh Observatory, College Hill, Armagh, BT61 9DG, Ireland (jgd,epp@star.arm.ac.uk)

Received 4 June 1999 / Accepted 30 August 1999

Abstract

High-resolution ultraviolet (UV) spectra of the outer solar atmosphere show transient brightenings often referred to as explosive events. These are localized regions of small spatial extent that show sudden enhancements in the intensities of lines formed between 20,000 and 200,000 K, accompanied by strong non-gaussian profiles.

The present work is an attempt to extract observational consequences from computational simulations of the dynamic response of a coronal loop to energy perturbations. Explosive events are simulated in semi-circular magnetic flux tubes. Thermal energy perturbations drive flows along the flux tube giving rise to thermodynamic phenomena. The temporal evolution of the thermodynamic state of the loop is converted into C IV  1548.2 Å line profiles in (non)-equilibrium ionization. Time dependent carbon ion populations are obtained in the non-equilibrium conditions derived from the thermodynamic variables by means of an adaptive grid code. Most important, departures from ionization equilibrium are assessed for the first time under conditions such as those encountered in explosive events.

Key words: Sun: atmosphere Sun: particle emission Sun: UV radiation

Send offprint requests to: L.M. Sarro

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Hydrodynamical simulations
  • 2.1. Physical layout
  • 2.2. Results
    • 2.2.1. Central simulation
    • 2.2.2. Exploration of the parameter space
• 3. Observational consequences
  • 3.1. Non-equilibrium ionization
  • 3.2. Line synthesis
• 4. Results
  • 4.1. s
  • 4.2. s
  • 4.3. s
• 5. Discussion
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: November 3, 1999
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