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We investigate spatio-temporal evolution of high-degree acoustic modefrequencies of the Sun and the surface magnetic activity, over the course ofmultiple solar cycles, to improve our understanding of the connection betweenthe solar interior and atmosphere. We focus on high-degree modes due to theirability to characterize conditions in the shear layer just below the solarsurface. Using the full-disk Doppler observations made by the GlobalOscillation Network Group (GONG), mode frequencies covering the period fromJuly 2001 to December 2021 are computed through the local helioseismictechnique of ring diagrams. Considering 10.7 cm radio flux measurements, thesunspot number, and the local magnetic activity index as solar activityproxies, we note strong correlation between the frequency shifts and eachactivity index. We further investigate the hemispheric asymmetry in frequencyshifts and magnetic activity and find that both the activity and frequencies inthe descending phase of cycle 23 were dominant in the southern hemisphere,while in cycle 24 these quantities fluctuated between northern and southernhemispheres. Analyzing the frequency shifts at different latitudes with theprogression of solar cycles, we observe that the shifts at mid-latitudes aredominant in the southern hemisphere during the maximum period of solar activityin cycle 24 but the values overlap as the cycle advances towards the minimumactivity period. The frequency shifts at the beginning of cycle 25 are found tobe dominant in the southern hemisphere following magnetic activity. Theanalysis presents additional evidence that the variability in oscillationfrequencies are caused by both strong and weak magnetic fields.

Connection between Sub-surface Layers and Surface Magnetic Activity over Multiple Solar Cycles