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In order to quantify the influence of magnetic fields on acoustic modeparameters and flows in and around active regions, we analyse the differencesin the parameters in magnetically quiet regions nearby an active region (whichwe call `nearby regions'), compared with those of quiet regions at the samedisc locations for which there are no neighboring active regions. We alsocompare the mode parameters in active regions with those in comparably locatedquiet regions. Our analysis is based on ring diagram analysis of all activeregions observed by HMI during almost five years. We find that the frequency atwhich the mode amplitude changes from attenuation to amplification in the quietnearby regions is around 4.2 mHz, in contrast to the active regions, for whichit is about 5.1 mHz. This amplitude enhancement (the `acoustic halo effect') isas large as that observed in the active regions, and has a very weak dependenceon the wave propagation direction. The mode energy difference in nearby regionsalso changes from a deficit to an excess at around 4.2 mHz, but averages tozero over all modes. The frequency difference in nearby regions increases withincreasing frequency until a point at which the frequency shifts turn oversharply as in active regions. However, this turnover occurs around 4.9 mHz,significantly below the acoustic cutoff frequency. Inverting the horizontalflow parameters in the direction of the neighboring active regions, we findflows that are consistent with a model of the thermal energy flow being blockeddirectly below the active region.

Statistical analysis of acoustic wave parameters near active regions