A Search for Discrete Acoustic and Gravitational Wave Sources

P.I.: T.M. Brown (HAO/NCAR)

Co-I: M.P. Rast (HAO/NCAR)

Abstract:

The excitation of solar acoustic oscillations is likely by turbulent convection. It has been suggested that localized well separated events may account for a significant fraction of the emitted energy (Brown 1991) since the efficiency of emission scales as a high power of the flow Mach number (Goldreich & Keeley 1977, Goldreich & Kumar 1990). It has also been suggested, based on simulations of compressible ionizing convection, that granular downflow velocities become supersonic below the photosphere particularly during granule fragmentation, and that sites of fragmentation are thus likely those of significant acoustic excitation (Rast et al 1993, Rast 1995). Recent ground based observations tentatively support new downflow sites as ones of significant acoustic flux (Rimmele et al. 1995). We proposed to use data from the Michelson Doppler Imager on board the Solar and Heliospheric Observatory to investigate these dynamical connections. In addition we propose to investigate a phenomenon recently identified during a search similar to that proposed above. Ring like disturbances propagating radially from isolated sites of high frequency acoustic emission have been identified in high resolution Doppler movies (Rast, Brown, & Tarbell). What is interesting about these is that they have been found to propagate at roughly one tenth the local sound speed and thus do not likely represent an acoustic pulse. Instead they may be the signature of surface gravity waves. We propose to search the SOI data for this phenomenon as well.