First Accurate, and Surprising, Observations of Solar Spectral Irradiance by the SIM/SORCE Instrument

Details First Accurate, and Surprising, Observations of Solar Spectral Irradiance by the SIM/SORCE Instrument First Accurate, and Surprising, Observations of Solar Spectral Irradiance by the SIM/SORCE Instrument

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21631304f&link_type=abstract

American Astronomical Society, AAS Meeting #216, #313.04; Bulletin of the American Astronomical Society, Vol. 41, p.888

Astronomy and Astrophysics

Astronomy

Scientific paper

It has been long speculated by the solar irradiance community that the observed Total Solar Irradiance (TSI) variations during the last few cycles were due to the active regions present on the solar disk at times of maximum sunspot index. Although sunspots darkness reduces the TSI, it was surmised that brightening in the surrounding facular and plage regions could over-compensate the sunspot effect.
The first accurate observations of Solar Spectral Irradiance (SSI) during the decay of solar cycle 23, by the SIM/SORCE instrument, showed larger changes in the solar spectrum that are not simply described by TSI variations.
These observations show much larger variation of the visible and IR ranges and of the opposite phase to those that were inferred from TSI proxies. Instead, the near-UV varies in phase with the TSI proxy but with amplitude much larger than was expected and the visible-IR power changes nearly compensate the UV leaving the residual small changes of the TSI. These solar cycle trends are much larger than the 27-day modulation due to the solar rotation, and cannot be fully explained by the passage of plage and sunspot on the disk.
Therefore, a paradigm change is needed in our study of SSI variations that requires a significant decrease in the photospheric temperature gradient at times of maximum solar activity. To explain the observations such a decrease must be relatively small but occur over areas of the solar surface much more extended than observed active regions. Increased energy transport efficiency in the active Sun's photosphere can explain this temperature gradient change.

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