23 January 2017 - Mission Day: 7724 - DOY: 023

Total Solar Irradiance, 1978 - 1999

    ./Total Solar Irradiance (TSI) observations
    Click on the image for a larger version
    Other formats: TIFF (927K), PostScript (228K), PDF (146K),

Caption: Measurements from six independent space-based radiometers since 1978 (top) have been combined to produce the composite total solar irradiance (TSI) over two decades (bottom). They show that the Sun's output fluctuates during each 11-year sunspot cycle, changing by about 0.1 percent between maxima (1980 and 1990) and minima (1987 and 1997) of solar activity. Temporary dips of up to 0.3 percent and a few days duration are the result of large sunspots passing over the visible hemisphere. The larger number of sunspots near the peak in the 11-year cycle is accompanied by a general rise in magnetic activity that creates an increase in the luminous output that exceeds the cooling effects of sunspots.

The data are from the Hickey-Frieden (HF) radiometer of the Earth Radiation Budget (ERB) experiment on the Nimbus-7 spacecraft (1978-1992), the two Active Cavity Radiometer Irradiance Monitors (ACRIM I and II) placed aboard the Solar Maximum Mission satellite (SMM, 1980-1989) and the Upper Atmosphere Research Satellite (UARS, 1991-), respectively, and the VIRGO radiometers flying on the SOlar and Heliospheric Observatory (SOHO, 1996-). Also shown are the data from the radiometer on the Earth Radiation Budget Satellite (ERBS, 1984-), and SOVA2 as part of the Solar Variability Experiment (SOVA) on the European Retrievable Carrier (EURECA, 1992-1993). Offsets among the various data sets are the direct result of uncertainties in the absolute radiometer scale of the radiometers (±0.3%). Despite these biases, each data set clearly shows varying radiation levels that track the overall 11-year solar activity cycle.


T.J. Quinn and C. Fröhlich. Accurate radiometers should measure the output of the sun. Nature, 401, 841, 1999.

C. Fröhlich and J. Lean. The sun's total irradiance: Cycles and trends in the past two decades and associated climate change uncertainties. Geophys. Res. Let., 25, 4377-4380, 1998.

Instruments: VIRGO + 5 other missions (see last paragraph of image caption); Taken: 1978-1999


• European Site • US Site


Feedback & Comments: SOHO Webmaster

Last modification:

SOHO is a project of international cooperation between