Multi-period variations during Solar Cycles 23–24

Solar periodicity is discovered in many magnetic activity indices (11 years, Rieger type 155-165 days, hundreds, and thousands of years). This research investigates multi-periodic variations in solar activity during Solar Cycles 23–24 and estimates the dynamo field strength. Daily sunspot area data from the Greenwich Royal Observatory were analyzed using Lomb-Scargle and Wavelet methods. These reveal multi-periodic variations (40–600 days) across the Sun’s full disk. The observed periods likely originate from magneto-Rossby waves in the solar dynamo layer. We estimate dynamo field strengths of 25–31 kG for Cycle 23 and 23–30 kG for Cycle 24 using wave dispersion relations.