HR: 1330h
AN: SH32A-1100    [PDF]
TI: Long-Term Total Irradiance Composites and Models
AU: Helizon, R
EM: roger@simdac.jpl.nasa.gov
AF: Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 United States
AU: * Pap, J M
EM: papj@marta.gsfc.nasa.gov
AF: University of Maryland Baltimore County, NASA Goddard Space Flight 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, continuous measurement programs must be formulated to compile composite irradiance time series from data of several experiments. Because the absolute accuracy of the current measurements is limited ($\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 (1997) concluded that the minimum of cycle 22 was higher than the minimum of cycle 21, while Fr\"ohlich and Lean (1998) claim that no trend can be seen in total irradiance within the current measurement accuracy. In this paper we compare various total irradiance time series and composites. Specifically, we will compare the Nimbus-7, ERBS, ACRIM~II and EURECA total irradiance data for the 1991-1993 time frame and the ACRIM~II, and VIRGO data for the time frame of 1996-2000 to clarify whether the minimma of cycles 21 and 22 are the same or they are indeed diffferent. Fr\"ohlich, C. and Lean, J.: 1998, In {\it Proceedings of the IAU Symposium 185}, (ed. F.L. Deubner), Kluwer Academic Publishers, p. 89. Willson, R.C.: 1997, {\it Science} {\bf 277}, 1963.
DE: 1650 Solar variability
DE: 7524 Magnetic fields
DE: 7536 Solar activity cycle (2162)
DE: 7538 Solar irradiance
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting