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Courtesy of NASA

Source article

Geophysical Research Letters

Published By

M.Sc. Armand van Wijck

Tags

climate, sun, irradiance, energy


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A new, lower value of total solar irradiance

21.01.2011, Age: 2832 days

Two scientists claim to have found a much lower value of total solar irradiance. They measured a total of 1360.8 ± 0.5 W m−2, instead of the canonical value of 1365.4 ± 1.3 W m−2.

This difference is by far not significantly larger than -for example- the 0.1% variation due to solar magnetic activity cycles. The authors however state that the lower solar irradiance value lies not within a change in the Sun's output, but in advancing the capability of monitoring solar irradiance variations on climate-relevant time scales and in improving estimates of the Earth energy balance. They published their article in Geophysical Research Letters on January 14.

From the abstract:

The most accurate value of total solar irradiance during the 2008 solar minimum period is 1360.8 ± 0.5 W m−2 according to measurements from the Total Irradiance Monitor (TIM) on NASA's Solar Radiation and Climate Experiment (SORCE) and a series of new radiometric laboratory tests. This value is significantly lower than the canonical value of 1365.4 ± 1.3 W m−2 established in the 1990s, which energy balance calculations and climate models currently use. Scattered light is a primary cause of the higher irradiance values measured by the earlier generation of solar radiometers in which the precision aperture defining the measured solar beam is located behind a larger, view-limiting aperture. In the TIM, the opposite order of these apertures precludes this spurious signal by limiting the light entering the instrument. We assess the accuracy and stability of irradiance measurements made since 1978 and the implications of instrument uncertainties and instabilities for climate research in comparison with the new TIM data. TIM's lower solar irradiance value is not a change in the Sun's output, whose variations it detects with stability comparable or superior to prior measurements; instead, its significance is in advancing the capability of monitoring solar irradiance variations on climate-relevant time scales and in improving estimates of Earth energy balance, which the Sun initiates.

Kopp, G., and J. L. Lean (2011), A new, lower value of total solar irradiance: Evidence and climate significance, Geophys. Res. Lett., 38, L01706, doi:10.1029/2010GL045777.


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