Changes in high-degree mode characteristics with magnetic activity

Abstract

We compare mode frequencies and other characteristics as determined from ring-diagram analysis of selected small regions of the Sun exhibiting strong variations in magnetic activity. These regions were observed with the Michelson Doppler Imager (MDI) on SOHO in its high-resolution mode during several years from solar minimum to maximum. To better understand the systematic uncertainties in fitting the ridges to the high-resolution data, we compare our results with those for the same regions concurrently observed in the MDI full-disc mode. We find that the properties of high degree p-modes are different in active and quiet regions and that the magnitude of the changes depend on the activity level.