Astron. Astrophys. 359, 1175-1184 (2000)

Wave modulation and wave sources in the solar convection zone

M. Kiefer ¹, M. Stix ¹ and H. Balthasar <sup>2

1</sup> Kiepenheuer-Institut für Sonnenphysik, Schöneckstrasse 6, 79104 Freiburg, Germany (kiefer,stix@kis.uni-freiburg.de)
² Astrophysikalisches Institut Potsdam, Telegrafenberg, 14473 Potsdam, Germany (hbalthasar@aip.de)

Received 21 December 1999 / Accepted 18 May 2000

Abstract

We investigate the behavior of upward running sound waves in the lower photosphere by means of a 2-hour time series of FPI-filtergrams and a corresponding series of white-light images. From the FPI-filtergrams we obtain velocities in two heights in the solar photosphere. Using specific filters in the --space, we extract running sound waves from the velocity time series and the granulation from the white-light series. The relation between granular structure and wave amplitude is examined. To this end the granulation images are subdivided into intensity classes. The amplitudes of the waves are extracted on the pixel maps corresponding to these classes. We find hints for wave modulation due to the inhomogeneities in the solar convection zone: The behavior of the wave amplitudes meets theoretical predictions with respect to frequency- and height-dependence. The dependence on the horizontal wave number meets the predictions too, but due to low wave coherence at high wave numbers no definitive statement is possible. Further the darkest locations in the granulation are preferred by waves of increased amplitudes. There also seems to be a preference for the brightest granular regions. In both cases the behavior of the waves can be well described by subsurface sound sources. This is confirmed by comparison of the data with a simple model of a subsurface sound source.

Key words: Sun: granulation Sun: oscillations convection waves

Present address: Institut für Meteorologie und Klimaforschung, Forschungszentrum Karlsruhe GmbH, Postfach 3640, 76021 Karlsruhe, Germany

Send offprint requests to: M. Kiefer (Michael.Kiefer@imk.fzk.de)

This article contains no SIMBAD objects.

Contents

• 1. Introduction
• 2. Models and theoretical considerations
  • 2.1. 2D models of the convection zone
  • 2.2. A simple model of a subsurface sound source
• 3. Observation and data preparation
• 4. Power in the diagnostic diagram and data filtering
• 5. Methods of data analysis
  • 5.1. Relations between running sound waves and granulation
  • 5.2. Radial distribution of intensity classes for the generation of synthetic observations
• 6. Results and discussion
  • 6.1. Comparison of synthetic and real observations
  • 6.2. Behavior of the running sound waves
    • 6.2.1. Dependence on frequency
    • 6.2.2. Dependence on height
    • 6.2.3. Dependence on wave number
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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