HR: 15:10h
AN: SH33C-06    [Abstracts]
TI: Satellite TSI Observations, Scales and Traceability in the context of the NASA-NIST TSI Workshop Day2 Presentations and Discussion
AU: * Willson, R C
EM: rwillson@acrim.com
AF: Columbia University, 12 Bahama Bend, Coronado, CA 92118 United States
AU: Helizon, R S
EM: roger.s.helizon@jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Dr., Pasadena, CA 91109-8089 United States
AB: Composite TSI time series have been constructed from the set of contiguous, redundant, overlapping total solar irradiance (TSI) observations made by satellite experiments since late 1978. A precise knowledge of the relationship between ACRIM1 and ACRIM2 across the two year gap separating their results is required and can be derived using one of two overlapping data sets: the Nimbus7/ERB or ERBS/ERBE. These two choices are demonstrated in the TSI composites published as the ACRIM (using the Nimbus7/ERB) [Willson & Mordvinov, 2003] and the PMOD (using the ERBS/ ERBE) [Frohlich & Lean, 1998] models. The ACRIM composite uses unaltered published results from a subset of satellite TSI data and detects an upward trend of 0.04 % per decade between activity minima during solar cycles 21-23. The PMOD composite uses a different subset of the same satellite TSI data and a different approach, modifying some results using linear regression TSI proxy models as a guide, and finds no significant trend. There are a number of differences between the ACRIM and PMOD composites but the most important is the trend difference. The absence of a minima-to-minima trend in composites based on the ERBS/ERBE ACRIM gap comparisons has been shown to be an artifact of uncorrected degradation of ERBE results during the gap. A three day NASA-NIST TSI Workshop was convened in 2005 to explore the scale and traceability issues of the extant satellite TSI database. The focus of Day1 was the difference between the radiometric scales defined by the UARS/ACRIM2, SOHO/VIRGO and ACRIMSAT/ACRIM3 experiments (which agree within 0.1 %) and the SORCE/TIM (lower by 0.4 %). The cause of the disagreement could not be resolved on the basis of the presentations by the experiment teams. The Day1 presentations and discussion will be addressed in detail by another paper in this session [Kopp et. al.]. The Day2 presentations and discussion centered around the experiment precision or traceability sustained by satellite TSI experiments. A general finding was that the as-launched performance of satellite TSI experiments usually fails to reach the pre-launch calibration expectations in either scale definition or traceability. One finding was that the ERBS/ERBE TSI sensor appears to have been operating in a degraded mode since its launch in 1984. Its shutter cycle appears to be too short to provide settled-out data for its servo-controlled cavity. The impacts on its calibration and traceability have yet to be determined but its usefulness as a comparison database in constructing a composite TSI time series is in question. Specific experiments at NIST and the JPL Table Mtn. Solar Test Facility were recommended during Day2 discussions to explore the scale differences further. Day3 of the Workshop, which addressed theoretical and laboratory approaches to improving our understanding of scale differences and instrument performances, will be discussed by another paper in this session [Rice].
UR: http://www.acrim.com
DE: 1600 GLOBAL CHANGE
DE: 1650 Solar variability (7537)
DE: 3359 Radiative processes
DE: 7538 Solar irradiance
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005