Flows, Random Motions and Oscillations in Solar Granulation Derived from the Soup Instrument on Spacelab 2
The Solar Optical Universal Polarimeter (SOUP) on Spacelab 2 collected movies of solar granulation that are completely free from the distortion and blurring introduced by the Earth’s atmosphere. Individual images in the movies are diffraction-limited (30 cm aperture) and are not degraded by pointing jitter (the pointing stability was 0.003″ root mean square). The movies illustrate that the solar five minute oscillation has a major role in the appearance of solar granulation and that exploding granules are a common feature of the granule evolution. Using 3-D Fourier filtering techniques, we have been able to remove the oscillations and demonstrate that they dominate the temporal autocorrelation functions (ACF) of the granulation pattern. When the oscillations are removed the autocorrelation lifetime of granulation is a factor of two greater in magnetic field regions than in field-free quiet sun. Using a technique called local correlation tracking we have been able to measure horizontal velocities and observe flow patterns on the scale of meso- and supergranulation. In quiet regions the mean flow velocity is 370 m/s while in magnetic regions it is about 125 m/s. We have also found that the root mean square (rms) fluctuating horizontal velocity field in quiet regions increases from 0.45 to 1.4 km/s and in strong magnetic field regions it increases from 0.3 to 0.75 km/s as the measuring aperture decreases from 4 to 1 arc seconds. Combining the results from temporal and spatial ACF’s with the velocity measurements, we conclude that the decay of the temporal ACF is due as much to motion and distortion of granules as to the lifetimes of elements in the pattern. By superimposing the location of exploding granules on the average flow maps we find that they appear almost exclusively in the center of mesogranulation size flow cells. The density of exploding granules is sufficient for their expansion fronts to cover a typical mesogranule in 900 seconds. Because of the non-uniformity of the distribution of exploding granules, the evolution of the granulation pattern in mesogranule cell centers and boundaries differs fundamentally. It is clear from this study that there is neither a typical granule nor a typical granule evolution. Even after the solar oscillations have been removed, a granule’s evolution is dependent on the local magnetic flux density, on its position with respect to the active region plage, on its position in the mesogranulation pattern, and on the evolution of granules in its immediate neighborhood.
KeywordsMagnetic Field Strength Pore Region Magnetic Region Quiet Region Solar Oscillation
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- Beckers, J.M., 1981, in The Sun as a Star, ed. Stuart Jordan (NASA SP-450), 11.Google Scholar
- Bonet, J. A., Marquez,T., Roca-Cortez, T., Vazquez, M., Wohl, H., Wittmann, A., 1984, in Small Scale Dynamical Processes in Quiet Stellar Atmospheres, ed. S. Keil, NSO conf., 323.Google Scholar
- Bray, R.J., Loughhead, R.E., and Durrant, C.J, 1984: The Solar Granulation Cambridge University Press.Google Scholar
- Cox, A., 1987, Ap. J., submitted.Google Scholar
- Livingston, W., 1984, in Small Scale Dynamical Processes in Quiet Stellar Atmospheres, ed. S. Keil, NSO conf., 330.Google Scholar
- Namba, O., Diemel, W. E., 1969, Solar Phys., 26, 290.Google Scholar
- Namba, O., van Rijsbergen, R., 1977, in Problems of Stellar Convection, IAU Coll.38, ed. E.A. Spiegel and J.P. Zahn, 119.Google Scholar
- Nordlund, A., 1984, in Small Scale Dynamical Processes in Quiet Stellar Atmospheres, ed. S. Keil, NSO conf., 174.Google Scholar
- November, L., Simon, G., Tarbell, T., Title, A., and Ferguson, S., 1987, in High Resolution Solar Physics II, ed. G. Athay and D. Spicer, NASA Conference Publication 2483, 121.Google Scholar
- Steffen, M., Ludwig, H.G., and Kruss, A., 1988, Astron. Astrophys., submitted.Google Scholar