F. Berrilli, L. Bertello, M. Cantoresi, S. Criscuoli

Reconstruction of the Total Solar Irradiance (TSI) over past epochs requires the evaluation of two major temporal components of solar activity: the quasi-cyclical component due to the 11-year sunspot cycle and the long-term component. We present here an empirical method to separate these components and to estimate the levels of the TSI during the last five centuries, an important information for global or regional climatology studies. We used available historical records of active region area coverage, reproduced by a functional form, and a time series of the Solar Modulation Potential to which we apply the Hilbert-Huang empirical mode decomposition (EMD) algorithm. The main finding of our study is that the estimated TSI values during the Maunder minimum and the present epoch differ by ~ 2.5 W/m2. By using this approach, we are also able to forecast the area coverage of active regions for solar cycle 25.