What Have We Learned from Sun's Acoustic Mode Frequencies over Three Decades?

The Sun's magnetic field varies in multiple timescales as evidenced by the emergence and decay of sunspots on the solar surface. Among these timescales, the 11-yr cyclic pattern, commonly known as Solar Activity Cycle, is the most prominent period. The acoustic oscillations observed at the surface of the Sun are known to correlate with the variations in solar magnetic activity. Availability of continuous helioseismic observations spanning over almost three decades from the ground and space suggest dynamical changes occurring in the solar interior. The long time series has allowed us to uncover several new features in helioseismic data that were inaccessible otherwise. Here we will present results on the temporal variability and various periodicities present in the oscillation frequencies. We will also discuss the spatiotemporal evolution of acoustic mode frequencies and the surface magnetic activity over the course of multiple solar cycles, to improve our understanding of the connection between the solar interior and atmosphere.