HR: 09:45h
AN: SH51E-07    [Abstracts]
TI: Long-Term Total Irradiance Composites
AU: * Pap, J M
EM: papj@marta.gsfc.nasa.gov
AF: GEST/UMBC, NASA Goddard Space Flicgh Center, Code 680.0, Greenbelt, MD 20771 United States
AB: Accurate long-term total and spectrally resolved solar irradiance measurements are required for full understanding of the response of Earth's atmosphere and climate to irradiance changes. Space-based irradiance observations over the last two and a half solar cycles span a time interval too short to reveal secular changes and/or to establish conclusively whether there are significant changes in the amplitude or the character of irradiance variations on longer time scales. Since the time period of interest far exceeds the lifespan of any single experiment, composite irradiance time series must be compiled from data of several irradiance experiments. Because the absolute accuracy of the current measurements is limited (about $\pm$0.2% in case of total irradiance), overlapping and redundant measurements are needed to ensure that the resulting composite data sets represent the ``true'' solar behavior. However, the largest obstacle in creating the current long-term total irradiance composite is the two-year gap between the SMM/ACRIM~I and UARS/ACRIM~II measurements. Adjustment of the ACRIM~I and ACRIM~II data now must be made through the Nimbus-7/ERB and/or the ERBE measurements. While using the published Nimbus-7/ERB data set, Willson and Mordvinov (2003) concluded that the minimum of cycle 22 was higher than the minimum of cycle 21, Fr\"ohlich (2004) claims that no trend can be seen in total irradiance within the current measurement accuracy. In this paper we compare various total irradiance time series, to better understand the differences between the two total irradiance composites. We will apply a new approach to adjust the ACRIM~I and ACRIM~II time series to further study the possible secular trend in total irradiance. Fr\"ohlich, C. 2004, In the Solar Variability and Its Effect on Earth's Climate, Eds. J. Pap and P. Fox, AGU Monograph, No. 141, p. 97. Willson, R.C. and Mordvinov, A.V.: 2003, Geophys. Res. Lett. Vol. 30, 3-1.
DE: 7524 Magnetic fields
DE: 7529 Photosphere
DE: 7536 Solar activity cycle (2162)
DE: 7538 Solar irradiance
DE: 7594 Instruments and techniques
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting