Un-interrupted Sun-as-a-star Helioseismic Observations over Multiple Solar Cycles

We analyze Sun-as-a-star observations spanning over solar cycles 22 -- 24 from the ground-based network BiSON and solar cycles 23 -- 24 collected by the space-based VIRGO and GOLF instruments on board the {\it SoHO} satellite. Using simultaneous observations from all three instruments, our analysis suggests that the structural and magnetic changes responsible for modifying the frequencies remained comparable between cycle 23 and cycle 24 but differ from cycle 22. Thus we infer that the magnetic layer of the Sun has become thinner since the beginning of cycle 23 and continues during the current cycle.