Giant Cell Convection and Helioseismic Linewidths

Details Giant Cell Convection and Helioseismic Linewidths Giant Cell Convection and Helioseismic Linewidths

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.1704k&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #17.04; Bulletin of the American Astronomical Society, Vol. 24, p.753

Astronomy and Astrophysics

Astronomy

Scientific paper

We predict that a detectable signature of solar giant cell convection should exist as a systematic pattern of linewidth broadening in the the spectra of solar acoustic oscillations. Using the giant cell convection model provided by G. Glatzmeier, we have constructed a suite of synthetic helioseismic images. When spatially filtered, these images display a pronounced widening of lines with azimuthal order near m = 0 of the spatial filter. Sectoral, or |m| =~ l lines, in contrast, experience no such broadening, producing a linewidth pattern dominatly parabolic in m/l. For selected multiplets, simulations show that central lines can be twice the width of their sectoral partners. This effect is manifest also as an overall broadening of the degenerate linewidth. Parameters characterizing the degenerate linewidth and the contrast of central to zonal linewidths display a smooth, nearly linear dependence on harmonic degree l in synthetic data. These effects should be detectable, given current le This linewidth pattern is not due to intrinsic damping, but is an apparent broadening traceable to the solar differential rotation rate, which dominates the modal frequency splitting, shifting unevenly the multiplet modal peak frequencies. The near degeneracy of central modes permits strong convective coupling, producing wide, highly hybridized central lines. In contrast sectoral lines are left as nearly purely Lorentzian functions in the frequency domain. Attempts to detect a contrast in multiplet linewidths are complicated by the multiplicative noise that is imposed on real data as a result of the solar source's stochastic character. We have developed a new spectral estimation technique to overcome this difficulty. Multiplet contrast parameters are recovered to within ~ 20

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