STATISTICAL ANALYSIS OF ACOUSTIC WAVE PARAMETERS NEAR SOLAR ACTIVE REGIONS

• Published in: The Astrophysical journal Vol. 827; no. 2; p. 140
• Main Authors: Rabello-Soares, M. Cristina, Bogart, Richard S., Scherrer, Philip H.
• Format: Journal Article
• Language: English
• Published: United States The American Astronomical Society 20.08.2016
• Subjects: ACOUSTICS; AMPLIFICATION; AMPLITUDES; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ATTENUATION; COMPARATIVE EVALUATIONS; Frequency shift; Halos; MAGNETIC FIELDS; Mathematical models; MHZ RANGE; OSCILLATIONS; Parameters; SOUND WAVES; SUN; Sun: activity; Sun: helioseismology; Sun: magnetic fields; Sun: oscillations; SUNSPOTS; WAVE PROPAGATION
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/0004-637X/827/2/140

ABSTRACT In order to quantify the influence of magnetic fields on acoustic mode parameters and flows in and around active regions, we analyze the differences in the parameters in magnetically quiet regions nearby an active region (which we call "nearby regions"), compared with those of quiet regions at the same disk locations for which there are no neighboring active regions. We also compare the mode parameters in active regions with those in comparably located quiet regions. Our analysis is based on ring-diagram analysis of all active regions observed by the Helioseismic and Magnetic Imager (HMI) during almost five years. We find that the frequency at which the mode amplitude changes from attenuation to amplification in the quiet nearby regions is around 4.2 mHz, in contrast to the active regions, for which it is about 5.1 mHz. This amplitude enhacement (the "acoustic halo effect") is as large as that observed in the active regions, and has a very weak dependence on the wave propagation direction. The mode energy difference in nearby regions also changes from a deficit to an excess at around 4.2 mHz, but averages to zero over all modes. The frequency difference in nearby regions increases with increasing frequency until a point at which the frequency shifts turn over sharply, as in active regions. However, this turnover occurs around 4.9 mHz, which is significantly below the acoustic cutoff frequency. Inverting the horizontal flow parameters in the direction of the neigboring active regions, we find flows that are consistent with a model of the thermal energy flow being blocked directly below the active region.