Can surface magnetic fields reproduce solar irradiance variations in cycles 22 and 23?

Total solar irradiance is reconstructed using data from the spectromagnetograph on Kitt Peak for 1992 - 2003 ( covering parts of cycles 22 and 23) and compared with observational data. The model assumes that solar irradiance variations are caused by surface magnetism and its single free parameter is kept at the same value for both cycles. A good correspondence is found for the whole period of time, with no bias between the two cycles on time-scales longer than the solar rotation period. This is in agreement with the recent results of de Toma et al. ( 2004), but it is in contrast to the earlier analysis of de Toma et al. ( 2001), and suggests that the source of the irradiance variations is the same for cycles 22 and 23, namely the evolution of the magnetic flux at the solar surface.