HR: 11:40h
AN: SH31C-06 INVITED     [PDF]
TI: Composite total solar irradiance time series show a secular 0.04 %/decade trend
AU: * Willson, R C
EM: rwillson@acrim.com
AF: Columbia University, 1001 B Ave., Ste 200, Coronado, CA 92118 United States
AU: Mordvinov, A V
EM: avm@iszf.irk.ru
AF: Siberian Branch of Russian Academy of Sciences, P.O. Box 4026, Irkutsk, Sib 664033 Russian Federation
AB: The satellite total solar irradiance (TSI) observational database extends over the past 25 years with useful precision for solar physics and climatology investigations. Willson \& Mordvinov (2003) reconciled the published results from various experiments to a common scale using overlapping comparisons to produce a composite TSI time series with sufficient precision to resolve a TSI trend of + 0.04 %/decade between successive solar activity minima. Key to this process is determining the relationship of the results of the non-overlapping ACRIM1 and ACRIM2 experiments. Two overlapping sets of results are available for this purpose: Nimbus7/ERB and the ERBS/ERBE. The ACRIM composite approach, using unaltered results published by the science teams of each experiment demonstrates a + 0.04 %/decade trend between the solar minima of 1986 and 1996 using the more precise Nimbus7/ERB data to relate ACRIM1 \& 2 results. The use of ERBS/ERBE results instead produces a negligibly small trend. This is shown to be the effect of uncorrected ERBS/ERBE degradation during the 2 year ACRIM gap whose magnitude and direction account for the trend difference precisely. A further illustration of this difference is the PMOD composite TSI model of Frohlich \& Lean (1998) which uses ERBS/ERBE results to relate ACRIM1 and ACRIM2. It differs from the ACRIM composite in two significant respects: a negligible trend between solar minima and lower TSI at solar maxima. Our findings indicate PMOD's lower trend and lower TSI during solar cycles 22 and 23 maxima result from their use of the ERBS/ERBE data and are therefore artifacts of its uncorrected degradation. Lower PMOD TSI during the maximum of cycle 21 is the result of the modifications of published Nimbus7/ERB and ACRIM1 data made to produce better agreement with a TSI solar proxy regression model. These modifications are not based on reevaluation of basic experiment data or algorithms and are therefore less likely to be correct than the analyses by the ACRIM and Nimbus7/ERB science teams. Lastly, it has not been demonstrated that regression models employed by the PMOD composite are competitive with satellite TSI observations in precision or traceability and are therefore of dubious value in justifying modifications of published TSI observations. References: Frohlich \& Lean, GRL., v. 25, 4377 (1998), Willson \& Mordvinov, GRL, v. 30, 1199 (2000)
UR: http://www.acrim.com
DE: 1650 Solar variability
DE: 7524 Magnetic fields
DE: 7529 Photosphere
DE: 7538 Solar irradiance
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting