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Astron. Astrophys. 349, 312-316 (1999)

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Damping and frequency reduction of the f -mode due to turbulent motion in the solar convection zone

M. Medrek 1, K. Murawski 1 and B. Roberts 2

1 Technical University of Lublin, ul. Nadbystrzycka 40, PL-20-618 Lublin, Poland
2 School of Mathematical and Computational Sciences, University of St Andrews, St Andrews, Fife KY16 9SS, Scotland

Received 12 February 1999 / Accepted 5 July 1999

Abstract

Solar f -mode properties were observed recently with high accuracy using high-resolution Michelson Doppler Imager (MDI) data from SOHO (Duvall et al. 1998). According to these observations, linewidths increase with wavenumber k and the f -mode frequency [FORMULA] is significantly lower than the frequency [FORMULA] given by the simple dispersion relation [FORMULA]. This paper provides a possible explanation of these observations on the basis of the turbulent flow that is in the convection zone. The f -mode spends more time propagating against the flow than with the flow. As a result, its effective speed and consequently frequency are reduced. This reduction is revealed by the real part of [FORMULA]. A negative imaginary part of the frequency [FORMULA] represents the damping of the coherent f -mode field due to scattering by the turbulent flow. The f -mode damping is a result of the generation of the turbulent field at the expense of the coherent field.

Key words: convection – Sun: atmosphere – Sun: granulation – Sun: oscillations – turbulence

Send offprint requests to: medrek@akropolis.pol.lublin.pl; kamur@akropolis.pol.lublin.pl.

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© European Southern Observatory (ESO) 1999

Online publication: August 25, 1999
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