Secular total solar irradiance trend during solar cycles 21–23

A series of satellite total solar irradiance (TSI) observations can be combined in a precise solar magnetic cycle length composite TSI database by determining the relationship between two non‐overlapping components: ACRIM1 and ACRIM2. [ Willson and Hudson , 1991 ; Willson , 1994 ] An ACRIM composite TSI time series using the Nimbus7/ERB results [ Hoyt et al. , 1992 ] to relate ACRIM1 and ACRIM2 demonstrates a secular upward trend of 0.05 percent‐per‐decade between consecutive solar activity minima. [ Willson , 1997 ] A PMOD TSI composite using ERBS [ Lee et al. , 1995 ] comparisons to relate ACRIM1 and ACRIM2 [ Fröhlich and Lean , 1998 ] differs from the ACRIM composite in two significant respects: a negligible trend between solar minima and lower TSI at solar maxima. Our findings indicate the lower PMOD trend and lower PMOD TSI at the maxima of solar cycles 22 and 23 are artifacts of ERBS degradation. Lower PMOD TSI during the maximum of cycle 21 results from modifications of Nimbus7/ERB and ACRIM1 published results that produces better agreement with a TSI/solar proxy model [ Foukal and Lean , 1988 ; Lean et al. , 1995 ; Fröhlich and Lean , 1998 ].