HR: 08:00h
AN: SH51E-01 INVITED     [Abstracts]
TI: Observations of Total Solar Irradiance indicate a + 0.04 % per decade trend during solar cycles 21 - 23
AU: * Willson, R C
EM: rwillson@acrim.com
AF: Columbia University, 12 Bahama Bend, Coronado, CA 92118 United States
AB: Continuous Total solar irradiance (TSI) observations have been made by satellite experiments since late 1978. A precise, contiguous composite TSI can be derived for the past 26 years by relating these results through consecutive overlapping observations. A crucial issue for a composite is the relationship between ACRIM1 and ACRIM2 results across the two year gap between them. This can be established by using one of the two overlapping data sets, the Nimbus7/ERB or ERBS/ERBE. The choice is important because the effects on the composite are significantly different. The ACRIM composite uses unaltered published results and the Nimbus7/ERB overlapping comparisons to link ACRIM1 and ACRIM2. The most significant feature of the ACRIM composite for climate change is an upward trend of 0.04 (+/- 0.01) % per decade between activity minima during solar cycles 21-23. [Willson & Mordvinov] TSI composites using the ERBS/ERBE data to link ACRIM1&2 results, such as the well known PMOD of Frohlich & Lean, use the same TSI data sets in a different approach but do not find a significant trend between minima. The absence of a trend in such ERBS/ERBE-based composites can be shown to be an artifact of uncorrected ERBS/ERBE degradation during the ACRIM1-ACRIM2 `gap'.There are other differences between the ACRIM and PMOD composites, driven principally by the PMOD's use of TSI proxy models to justify modifying the published results of ACRIM1 and Nimbus7/ERB. TSI regression (proxy) models based on chromospheric spectral features are not competitive in accuracy, precision or traceability with satellite TSI observations and are therefore likely to cause spurious effects when used in the construction of TSI composites. The TSI record has been sustained by overlapping, redundant experiments using their level of measurement precision to sustain longer term traceability. This TSI monitoring strategy is essential for continuity in the future because the uncertainty of current satellite sensors (~ 0.1 %) is an order of magnitude too large to detect subtle long term TSI variations of potential climate change significance. [Willson, R.C., A. V. Mordvinov, JGRL 30, pp. 1199-1202, 2003, Frohlich C., J. Lean, JGRL 25, pp. 4377-4380, 1998]
UR: http://www.acrim.com
DE: 7538 Solar irradiance
DE: 3359 Radiative processes
DE: 1600 GLOBAL CHANGE (New category)
DE: 1650 Solar variability
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting