Louis H. Strous

On the Origin of Solar Oscillations

We have made high-resolution observations of the Sun in which we identify individual sunquakes and see power from these seismic events being pumped into the resonant modes of vibration of the Sun. A typical event lasts about 5 minutes. We report the physical properties of the events and relate them to theories of the excitation of solar oscillations. We also discuss the local seismic potential of these events.

THE DYNAMICS OF THE EXCITATION OF SOLAR OSCILLATIONS

We investigate seismic events, bursts of seismic waves that are generated locally just below the solar surface and that we detect traveling up through the photosphere. We identify a few thousand seismic events by their traveling wave character and —nd that they are associated with continuum darkening and down—ow and have an extent of on average about 10¨15 minutes and 1 Mm. Their birth rate is about 8 ) 10~16 m~2 s ~1. The observed upwardly traveling seismic —ux in the average event (as derived from velocities in the p-mode region of k-u space) is followed after about 3 minutes by some re—ected down- ward —ux. Only a small fraction of the energy generated in the hypocenter of the event below the surface travels straight up for us to see. The bulk of the generated energy is directed or re—ected downward, and is eventually transformed into p-modes. The seismic events at the surface contain about 1.5 ) 1019 Jo f seismic energy each, which corresponds to an average —ux level of about 8.5 kW m~2 over the whole surface. The total energy —ow is likely more than an order of magnitude greater, and is then in the same ballpark as the estimate of Libbrecht for the power required to sustain the p-mode spectrum. We —nd a roughly linear relation between the peak seismic —ux and the peak downward convective velocity associ- ated with each seismic event, which does not —t the highly nonlinear relations found theoretically by Lighthill and Goldreich & Kumar for stochastic excitation by turbulent convection, but does —t the monopole source deduced by Nigam & Kosovichev from a study of the p-mode spectrum. Subject heading: Sun: oscillationsSun: photospherewaves