Acoustic Power Maps of Solar Active Regions

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Abstract
Using observations made by the Michelson Doppler Imager (MDI), we find that within solar active regions the spatial distributions of Doppler velocity power and continuum intensity power differ. The oscillation power within any pixel is a strong function of the magnetic field strength within that pixel. The amplitudes of oscillations with frequencies less than 5.2 mHz decrease with field strength for both velocity and continuum intensity measurements. However, within active regions oscillations with frequencies between 5.2 and 7.0 mHz have suppressed continuum intensity amplitudes but enhanced velocity amplitudes. The enhancement of the high-frequency velocity signal is largest in pixels with intermediate field strength (50-250 G) and is a manifestation of the high-frequency acoustic halos. We find that the high-frequency halos are absent in MDI observations of the continuum intensity.