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In this letter, we explore the relationship between the solar seismic radiusand total solar irradiance (TSI) during last two solar cycles using theuninterrupted data from space-borne instruments onboard {\it SoHO} and {\itSDO}. The seismic radius is calculated from the fundamental ({\it f}) modes ofsolar oscillations utilizing the observations from {\it SoHO}/MDI and {\itSDO}/HMI, and the total solar irradiance measurements are obtained from {\itSoHO}/VIRGO. Our study suggests that the major contribution to the TSIvariation arises from the changes in magnetic field while the radius variationplays a secondary role. We find that the solar irradiance increases withdecreasing seismic radius, however the anti-correlation between them ismoderately weak. The estimated maximum change in seismic radius during a solarcycle is about 5 kilometers, and is consistent in both solar cycles 23 and 24.Previous studies suggest a radius change at the surface of the order of 0.06arcsecond to explain the 0.1\% variation in the TSI values during the solarcycle, however our inferred seismic radius change is significantly smaller,hence the TSI variations can not be fully explained by the temporal changes inseismic radius.

Sun's Seismic Radius as Measured from the Fundamental Modes of Oscillations and its Implications for the TSI Variations