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Variability in the Power Spectrum of Solar Five-Minute Oscillations*

Published online by Cambridge University Press:  12 April 2016

Frank Hill ,
Juri Toomre  and
Laurence J. November
Frank Hill
Affiliation:
Department of Astrophysical, Planetary and Atmospheric Sciences**, and Joint Institute for Laboratory Astrophysics†, University of Colorado, Boulder, CO 80309, U.S.A.
Juri Toomre
Affiliation:
Department of Astrophysical, Planetary and Atmospheric Sciences**, and Joint Institute for Laboratory Astrophysics†, University of Colorado, Boulder, CO 80309, U.S.A.
Laurence J. November
Affiliation:
Air Force Geophysics Laboratory and AURA, Sacramento Peak Observatory, Sunspot, NM88349, U.S.A.

Abstract

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Two-dimensional power spectra of solar five-minute oscillations display prominent ridge structures in (k, ω) space, where k is the horizontal wavenumber and ω is the temporal frequency. The positions of these ridges in k and ω can be used to probe temperature and velocity structures in the subphotosphere. We have been carrying out a continuing program of observations of five-minute oscillations with the diode array instrument on the vacuum tower telescope at Sacramento Peak Observatory (SPO). We have sought to establish whether power spectra taken on separate days show shifts in ridge locations; these may arise from different velocity and temperature patterns having been brought into our sampling region by solar rotation. Power spectra have been obtained for six days of observations of Doppler velocities using the Mg I λ5173 and Fe I λ5434 spectral lines. Each data set covers 8 to 11 hr in time and samples a region 256″ × 1024″ in spatial extent, with a spatial resolution of 2″ and temporal sampling of 65 s. We have detected shifts in ridge locations between certain data sets which are statistically significant. The character of these displacements when analyzed in terms of eastward and westward propagating waves implies that changes have occurred in both temperature and horizontal velocity fields underlying our observing window. We estimate the magnitude of the velocity changes to be on the order of 100 m s -1; we may be detecting the effects of large-scale convection akin to giant cells.

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 66: Problems of Solar and Stellar Oscillations , 1983 , pp. 411 - 425
Copyright
Copyright © Reidel 1983

Footnotes

**

Formerly Department of Astro-Geophysics.

†

JILA is operated jointly by the University of Colorado and the National Bureau of Standards.

*

Proceedings of the 66th IAU Colloquium: Problems in Solar and Stellar Oscillations, held at the Crimean Astrophysical Observatory, U.S.S.R., 1-5 September, 1981.

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