Astron. Astrophys. 336, 1029-1038 (1998)

The heating of solar magnetic flux tubes

I. Adiabatic longitudinal tube waves

Diaa E. Fawzy ¹, P. Ulmschneider ¹ and M. Cuntz <sup>2, 1

1</sup> Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstr. 15, D-69121 Heidelberg, Germany
² Center for Space Plasma, Aeronomy, and Astrophysics Research (CSPAAR), TH S101, University of Alabama in Huntsville, Huntsville, AL 35899, USA

Received 30 October 1997 / Accepted 5 May 1998

Abstract

We study the formation of shocks and shock heating by adiabatic longitudinal tube waves in solar magnetic flux tubes of different shape. Monochromatic waves with periods between 20 and 160 s and energy fluxes ranging from to erg cm^-2s^-1 were considered. It is found that the tube shape is of critical importance for the heating of flux tubes. Constant cross-section tubes show large heating, whereas exponentially spreading tubes show little or no heating at all. In tubes of intermediate shapes ("wine-glass tubes"), the heating is essentially restricted to those regions, where the tube has attained its maximum diameter. This finding is in good agreement with the observation that the chromospheric network can still be seen well above the canopy height. In tubes of lower field strength, the shock formation is delayed and heating is reduced.

Key words: magnetohydrodynamics (MHD) shock waves waves Sun: chromosphere Sun: magnetic fields Sun: photosphere

Send offprint requests to: P. Ulmschneider
Correspondence to: ulmschneider@ita.uni-heidelberg.de

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Method
  • 2.1. Magnetohydrodynamic equations
  • 2.2. Shocks
  • 2.3. Flux tube models
  • 2.4. Wave computations
• 3. Results
  • 3.1. Varying the tube shape and the wave period
  • 3.2. Dependence on the wave energy
  • 3.3. Behaviour of the mean flow velocity
  • 3.4. Dependence on the magnetic flux
  • 3.5. Chromospheric emission contrast in relation to the tube models
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998
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