Ring diagram analysis of the characteristics of solar oscillation modes in active regions

Abstract

The presence of intense magnetic fields in and around sunspots is expected to modify solar structure and oscillation frequencies. Applying the ring diagram technique to data from the Michelson Doppler Imager on board the Solar and Heliospheric Observatory, we analyze the characteristics of high-degree f- and p-modes near active regions and compare them with the characteristics of the modes in quiet regions. As expected from earlier results, the f- and p-mode frequencies of high-degree modes are found to be significantly larger in magnetically active regions. In addition, we find that the power in both f- and p-modes is lower in active regions while the widths of the peaks are larger, indicating smaller lifetimes. We also find that the oscillation modes are more asymmetric in active regions than those in quiet regions, indicating that modes in active regions are excited closer to the surface. While the increase in mode frequency is monotonic in frequency, all other characteristics show more complex frequency dependences.