HR: 10:40h
AN: GC42A-02 INVITED    [Abstracts]
TI: Measurement of the Total Solar Irradiance over cycle 23: results from DIARAD/VIRGO.
AU: * Dewitte, S
EM: Steven.Dewitte@oma.be
AF: Royal Meteorological Institute of Belgium, Ringlaan 3, Brussels, B-1180, Belgium
AU: Mekaoui, S
EM: Sabri.Mekaoui@oma.be
AF: Royal Meteorological Institute of Belgium, Ringlaan 3, Brussels, B-1180, Belgium
AU: Crommelynck, D
EM: Dominique.Crommelynck@oma.be
AF: Royal Meteorological Institute of Belgium, Ringlaan 3, Brussels, B-1180, Belgium
AB: The Total Solar Irradiance (TSI) is measured from space since 29 years, covering 2.6 11 year solar cycles. Over the last 12 years, covering solar cycle 23, TSI measurements are available from the VIRGO experiment on the SOHO satellite. SOHO is located at the L1 Lagrange point, offering continuous sun observation and a stable thermal environment. VIRGO contains two independent radiometers, DIARAD and PMO, each with their own ageing monitoring capabilities. From these two radiometers, DIARAD is the only one with a nominal operation over the entire mission, and DIARAD has the lowest ageing. We present the ageing correction of DIARAD and PMO by the DIARAD team, and discuss the differences with the versions available from the PMO team. In addition to the normal exposure dependent ageing corrections applied by both the DIARAD and PMO teams, the PMO team applies additional 'exposure independent corrections' or 'sensitivity changes' which create an artificial downward trend of about 0.4 W/m2 for both DIARAD and PMO. Besides the two independent measurements of the TSI variation over cycle 23 from DIARAD and PMO, two more independent measurements over the complete cycle are available, on the one hand from a combination of ACRIM 2 and ACRIM 3, on the other hand from a combination of ERBS and TIM. All together, these measurements allow to measure the decadal trend of the TSI variation over cycle 23 with an unprecedented accuracy. All instruments show a similar long term behaviour except ACRIM 3 which shows a faster decline. We construct a composite time series using DIARAD/VIRGO as a reference instrument to put all instruments at the same absolute level. From the composite time series we can conclude there is no significant decadal trend during cycle 23. This is in contradiction with the ACRIM composite which shows a decreasing trend due to the ACRIM 3 decline, and with the PMO composite which shows a decreasing trend due to the 'exposure independent corrections' applied to the VIRGO radiometers.
DE: 7538 Solar irradiance
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting