Astron. Astrophys. 324, 587-596 (1997)

Acoustic wave propagation in the solar atmosphere

IV. Nonadiabatic wave excitation with frequency spectra

J. Theurer ¹, P. Ulmschneider ¹ and M. Cuntz <sup>1, 2

1</sup> Institut für Theoretische Astrophysik der Universität Heidelberg, Tiergartenstr. 15, D-69121 Heidelberg, Germany
² Center for Space Plasma and Aeronomic Research (CSPAR), EB 136M, University of Alabama in Huntsville, Huntsville, AL 35899, USA

Received 20 October 1996 / Accepted 29 January 1997

Abstract

We study the response of the solar atmosphere to excitations by large amplitude acoustic waves with radiation damping now included. Monochromatic adiabatic waves, due to unbalanced heating, generate continuously rising chromospheric temperature plateaus in which the low frequency resonances quickly die out. All non-adiabatic calculations lead to stable mean chromospheric temperature distributions determined by shock dissipation and radiative cooling. For non-adiabatic monochromatic wave excitation, a critical frequency  Hz is confirmed, which separates domains of different resonance behaviour. For waves of , the resonances decay, while for waves of persistent resonance oscillations occur, which are perpetuated by shock merging. Excitation with acoustic frequency spectra produces distinct dynamical mean chromosphere models where the detailed temperature distributions depend on the shape of the assumed spectra. The stochasticity of the spectra and the ongoing shock merging lead to a persistent resonance behaviour of the atmosphere. The acoustic spectra show a distinct shape evolution with height such that at great height a pure 3 min band becomes increasingly dominant. With our Eulerian code we did not find appreciable mass flows at the top boundary.

Key words: hydrodynamics shock waves waves Sun: chromosphere Sun: oscillations

Send offprint requests to: P. Ulmschneider

Contents

• 1. Introduction
• 2. Wave calculation method, Fourier analysis, atmosphere model
• 3. Results
  • 3.1. Monochromatic adiabatic wave excitation
  • 3.2. Effect of the generated chromosphere model, adiabatic case
  • 3.3. Monochromatic non-adiabatic wave excitation
  • 3.4. Effect of the generated chromosphere model, non-adiabatic case
  • 3.5. Excitation by acoustic spectra for non-adiabatic waves
  • 3.6. Shock merging and the generation of 3 min oscillations
  • 3.7. Acoustic spectra and the dynamic structure of the atmosphere
• 4. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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