New ideas about granulation based on data from the solar optical universal polarimeter instrument on spacelab 2 and magnetic data from big bear solar observatory

Abstract

The Solar Optical Universal Polarimeter (SOUP) on Spacelab 2 collected time sequences of diffraction limited (0.5 are second) granulation images with excellent pointing (.003 arc seconds) and freedom from the distortion that plagues groundbased images. The solar 5 minute oscillations are clearly seen in the data. Using Fourier transforms in the temporal and spatial domains, we have shown that oscillations have an important effect on the autocorrelation (AC) lifetime. When the oscillations are removed the autocorrelation lifetime is found to increase from 270 seconds to 410 and 890 seconds in quiet and magnetic regions, respectively. Exploding granules are common and it is hard to find a granule that neither explodes nor is unaffected by an nearby explosion. We speculate that a significant fraction of granule lifetimes are terminated by nearby explosions. Via local correlation tracking techniques we have been able to measure horizontal displacements, and thus transverse velocities, in the intensity field. It is possible to detect both super and mesogranulation. Horizontal velocities are as great as 1000 m/s in quiet sun and the average velocity is 400 m/s and 100 m/s in quiet and magnetic sun, respectively. These flow fields affect the measured AC lifetimes. After correcting for steady flow, we estimate a lower limit to the lifetime in quiet and magnetic sun to be 440 and 950 seconds, respectively. The SOUP flow fields have been compared with carefully aligned magnetograms taken at the Big Bear Solar Observatory (BBSO) before, during, and after the SOUP images. The magnetic field is observed to exist in locations where either the flow is convergent or on the boundaries of the outflow from a flow cell center. Streamlines calculated from the flow field agree very well with the observed motions of the magnetic field in the BBSO magnetogram movies.